2716 lines
149 KiB
Plaintext
2716 lines
149 KiB
Plaintext
The Linux 2.4 SCSI subsystem HOWTO
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Douglas Gilbert
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<dgilbert at interlog dot com>
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Copyright (c) 2001, 2002, 2003, 2004 Douglas Gilbert
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2003-08-24
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Revision History
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Revision 2.1 2004-08-24 Revised by: dpg
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scsihosts change -> run mkinitrd, lk 2.4.21,22
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Revision 2.0 2003-05-04 Revised by: dpg
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lk2.4.20, linuxdoc->tldp, sATA and SAS, last sector on raw devs, blockdev
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Revision 1.9 2002-11-20 Revised by: dpg
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convert to xml, lk2.4.19, spelling
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Revision 1.8 2002-05-05 Revised by: dpg
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scsihosts comma delimiter, grub+lilo
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Revision 1.7 2002-04-27 Revised by: dpg
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mkinitrd, scsi_debug, 2.4.18, more ATAPI
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Revision 1.6 2002-01-26 Revised by: dpg
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ATAPI cdrom selection
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Revision 1.5 2001-12-21 Revised by: dpg
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16 byte SCSI commands, SCSI_IOCTL_GET_PCI
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Revision 1.4 2001-08-26 Revised by: dpg
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spelling, dd_rescue, mkinitrd example, lk 2.4 changes, 1394.
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Revision 1.3 2001-08-26 Revised by: dpg
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ATAPI CDROM section, alter title, U320, iSCSI.
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Revision 1.2 2001-03-25 Revised by: dpg
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Information about scu, dt, "Alt" sequences, more notes.
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Revision 1.1 2001-01-22 Revised by: dpg
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Add osst description, _EXTRA_DEVS limitations.
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This document describes the SCSI subsystem as the Linux kernel enters the
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2.4 production series. An external view of the SCSI subsystem is the main
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theme. Material is included to help the system administration of the Linux
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SCSI subsystem. There are also brief descriptions of ioctl()s and interfaces
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that may be relevant to those writing applications that use this subsystem.
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Permission is granted to copy, distribute and/or modify this document under
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the terms of the GNU Free Documentation License, Version 1.1 or any later
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version published by the Free Software Foundation; with no Invariant
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Sections, with no Front-Cover Texts, and with no Back-Cover Texts.
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For an online copy of the license see www.fsf.org/copyleft/fdl.html.
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-----------------------------------------------------------------------------
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Table of Contents
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1. Introduction
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2. Architectural Overview
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3. Names and Addresses
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3.1. SCSI Addressing
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3.2. Device Names
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3.3. Device Names in devfs
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3.4. Device Names in scsidev
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4. Kernel Configuration
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5. Boot Parameters
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6. Modules and their Parameters
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7. Proc pseudo file system
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8. Mid Level, Unifying layer
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8.1. boot parameters
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8.2. module parameters
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8.3. proc interface
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9. Upper level drivers
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9.1. Disk driver (sd)
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9.2. CDROM driver (sr or scd)
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9.3. Tape driver (st)
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9.4. Generic driver (sg)
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10. Lower Level drivers
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10.1. Pseudo drivers
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11. Raw devices
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12. Devfs pseudo file system
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A. Common bus types (SCSI and other)
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B. Changes between lk 2.2 and (during) 2.4
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B.1. Mid level changes
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B.2. sd changes
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B.3. sr changes
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B.4. st changes
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B.5. sg changes
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B.6. Changes during the lk 2.4 series
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C. Troubleshooting
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D. Performance, Test and Debugging tools
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E. Compile options and System calls including ioctls
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E.1. Mid level
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E.2. sd driver
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E.3. sr driver
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E.4. st driver
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E.5. sg driver
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F. References, Credits and Corrections
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-----------------------------------------------------------------------------
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Chapter 1. Introduction
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This document describes the SCSI subsystem as the Linux kernel enters the
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2.4 production series.
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An external view of the SCSI subsystem is the main theme. Material is
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included to help the system administration of the Linux SCSI subsystem. There
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are also brief descriptions of ioctl()s and interfaces that may be relevant
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to those writing applications that use this subsystem. However internal data
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structures and design issues are not addressed [see reference W2]. To
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unclutter the presentation, compile options and system calls (including ioctl
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()s) have been placed in Appendix E. Although not strictly part of the SCSI
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subsystem, there is also a description of raw devices in Chapter 11.
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For those who have no interest in the SCSI subsystem and just want to get
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their ATAPI cd writer going, see Section 9.2.4. It may also be useful to
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browse Chapter 2.
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This document follows on from one written five years ago by Drew Eckhardt
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called the SCSI-HOWTO [see reference W7]. That document described the SCSI
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subsystem in Linux kernel 1.2 and 1.3 series. It is still available from the
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Linux Documentation Project [LDP, see reference W8] in its "unmaintained"
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section. Both documents have roughly similar structures although Drew's
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document has a lot of information on the adapter drivers.
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This document can be found in electronic form at www.tldp.org/HOWTO/
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SCSI-2.4-HOWTO. The home site and perhaps the most up to date version of this
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document can be found at www.torque.net/scsi/SCSI-2.4-HOWTO (this is the
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multi-page html version). At that location this document is rendered in txt,
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pdf, ps, a single (long) page of html as well as multi-page html. For
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example, a pdf version is at www.torque.net/scsi/SCSI-2.4-HOWTO.pdf).
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This document was last altered on 24th August 2004.
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-----------------------------------------------------------------------------
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Chapter 2. Architectural Overview
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The SCSI subsystem has a 3 level architecture with the "upper" level being
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closest to the user/kernel interface while the "lower" level is closest to
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the hardware. The upper level drivers are commonly known by a terse two
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letter abbreviation (e.g. "sd" for SCSI disk driver). The names of the
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corresponding module drivers which, for historical reasons, sometimes differ
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from the built in driver names are shown in braces in the following diagram.
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[scsi-arch]
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The 3 level driver architecture of the SCSI subsystem.
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The upper level supports the user-kernel interface. In the case of sd and sr
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this is a block device interface while for st and sg this is a character
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device interface. Any operation using the SCSI subsystem (e.g. reading a
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sector from a disk) involves one driver at each of the 3 levels (e.g. sd,
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SCSI mid level and aic7xxx drivers).
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As can be seen from the diagram, the SCSI mid level is common to all
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operations. The SCSI mid level defines internal interfaces and provides
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common services to the upper and lower level drivers. Ioctls provided by the
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mid level are available to the file descriptors belonging to any of the 4
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upper level drivers.
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The most common operation on a block device is to "mount" a file system. For
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a sd device typically a partition is mounted (e.g. mount -t ext2 /dev/sda6 /
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home). For a sr device usually the whole device is mounted (e.g. mount -t
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iso9660 /dev/sr0 /mnt/cdrom). The dd command can be used to read or write
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from block devices. In this case the block size argument ("bs") needs to be
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set to the block size of the device (e.g. 512 bytes for most disks) or an
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integral multiple of that device block size (e.g. 8192 bytes). A recent
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addition to the block subsystem allows a device (or partition) to be mounted
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more than once, at different mount points.
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Sd is a member of the generic disk family, as is the hd device from the IDE
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subsystem. Apart from mounting sd devices, the fdisk command is available to
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view or modify a disk's partition table. Although the hdparm command is
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primarily intended for ATA disks (also known as IDE or EIDE disks), some
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options work on SCSI disks.
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Sr is a member of the CD-ROM subsystem. Apart from mounting file systems
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(e.g. iso9660), audio CDs can also be read. The latter action does not
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involve mounting a file system but typically by invoking some ioctls. General
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purpose Linux commands such as dd cannot be used on audio CDs.
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St is a char device for reading and writing tapes. Typically the mt command
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is used to perform data transfers and other control functions.
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Sg is a SCSI command pass through device that uses a char device interface.
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General purpose Linux commands should not be used on sg devices. Applications
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such as SANE (for scanners), cdrecord and cdrdao (for cd writers) and
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cdparanoia (for reading audio CDs digitally) use sg.
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-----------------------------------------------------------------------------
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Chapter 3. Names and Addresses
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This section covers the various naming schemes that exist in Linux and the
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SCSI worlds and how they interact.
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-----------------------------------------------------------------------------
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3.1. SCSI Addressing
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Linux has a four level hierarchical addressing scheme for SCSI devices:
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<EFBFBD><EFBFBD>*<2A>SCSI adapter number [host]
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<EFBFBD><EFBFBD>*<2A>channel number [bus]
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<EFBFBD><EFBFBD>*<2A>id number [target]
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<EFBFBD><EFBFBD>*<2A>lun [lun]
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"Lun" is the common SCSI abbreviation of Logical Unit Number. The terms in
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brackets are the name conventions used by device pseudo file system (devfs).
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"Bus" is used in preference to "channel" in the description below.
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The SCSI adapter number is typically an arbitrary numbering of the adapter
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cards on the internal IO buses (e.g. PCI, PCMCIA, ISA etc) of the computer.
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Such adapters are sometimes termed as HBAs (host bus adapters). SCSI adapter
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numbers are issued by the kernel in ascending order starting with 0.
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Each HBA may control one or more SCSI buses. The various types of SCSI buses
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are listed in Appendix A.
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Each SCSI bus can have multiple SCSI devices connected to it. In SCSI
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parlance the HBA is called the "initiator" and takes up one SCSI id number
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(typically 7). The initiator [1] talks to targets which are commonly known as
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SCSI devices (e.g. disks). On SCSI parallel buses the number of ids is
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related to the width. 8 bit buses (sometimes called "narrow") can have 8 SCSI
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ids of which 1 is taken by the HBA leaving 7 for SCSI devices. Wide SCSI
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buses are 16 bits wide and can have a maximum of 15 SCSI devices (targets)
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attached. The SCSI 3 draft standard allows a large number of ids to be
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present on a SCSI bus.
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Each SCSI device can contain multiple Logical Unit Numbers (LUNs). These are
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typically used by sophisticated tape and cdrom units that support multiple
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media.
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So Linux's flavour of SCSI addressing is a four level hierarchy:
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<scsi(_adapter_number), channel, id, lun>
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Using the naming conventions of devfs this becomes:
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<host, bus, target, lun>
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-----------------------------------------------------------------------------
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3.2. Device Names
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A device name can be thought of as a gateway to a kernel driver that
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controls a device rather than the device itself. Hence there can be multiple
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device names some of which may offer slightly different characteristics, all
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mapping to the same actual device.
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The device names of the various SCSI devices are found within the /dev
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directory. Traditionally in Linux, SCSI devices have been identified by their
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major and minor device number rather than their SCSI bus addresses (e.g. SCSI
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target id and LUN). The device pseudo file system (devfs) moves away from the
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major and minor device number scheme and for the SCSI subsystem uses device
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names based on the SCSI bus addresses [discussed later in Section 3.3 and see
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reference: W5]. Alternatively, there is a utility called scsidev which
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addresses this issue within the scope of the Linux SCSI subsystem and thus
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does not have the same system wide impact as devfs. Scsidev is discussed
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later in Section 3.4 and ref: W6.
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Eight block major numbers are reserved for SCSI disks: 8, 65, 66, 67, 68,
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69, 70 and 71. Each major can accommodate 256 minor numbers which, in the
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case of SCSI disks, are subdivided as follows:
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[b,8,0] /dev/sda
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[b,8,1] /dev/sda1
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....
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[b,8,15] /dev/sda15
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[b,8,16] /dev/sdb
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[b,8,17] /dev/sdb1
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....
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[b,8,255] /dev/sdp15
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The disk device names without a trailing digit refer to the whole disk (e.g.
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/dev/sda) while those with a trailing digit refer to one of the 15 allowable
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partitions [2] within that disk.
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The remaining 7 SCSI disk block major numbers follow a similar pattern:
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[b,65,0] /dev/sdq
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[b,65,1] /dev/sdq1
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....
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[b,65,159] /dev/sdz15
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[b,65,160] /dev/sdaa
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[b,65,161] /dev/sdaa1
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....
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[b,65,255] /dev/sdaf15
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[b,66,0] /dev/sdag
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[b,66,1] /dev/sdag1
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....
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[b,66,255] /dev/sdav15
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....
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[b,71,255] /dev/sddx15
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So there are 128 possible disks (i.e. /dev/sda to /dev/sddx) each having up
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to 15 partitions. By way of contrast, the IDE subsystem allows 20 disks (10
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controllers each with 1 master and 1 slave) which can have up to 63
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partitions each.
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SCSI CD-ROM devices are allocated the block major number of 11.
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Traditionally sr has been the device name but scd probably is more
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recognizable and is favoured by several recent distributions. 256 SCSI CD-ROM
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devices are allowed:
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[b,11,0] /dev/scd0 [or /dev/sr0]
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[b,11,255] /dev/scd255 [or /dev/sr255]
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SCSI tape devices are allocated the char major number of 9. Up to 32 tape
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devices are supported each of which can be accessed in one of four modes (0,
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1, 2 and 3), with or without rewind. The devices are allocated as follows:
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[c,9,0] /dev/st0 [tape 0, mode 0, rewind]
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[c,9,1] /dev/st1 [tape 1, mode 0, rewind]
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....
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[c,9,31] /dev/st31 [tape 31, mode 0, rewind]
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[c,9,32] /dev/st0l [tape 0, mode 1, rewind]
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....
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[c,9,63] /dev/st31l [tape 31, mode 1, rewind]
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[c,9,64] /dev/st0m [tape 0, mode 2, rewind]
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....
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[c,9,96] /dev/st0a [tape 0, mode 3, rewind]
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....
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[c,9,127] /dev/st31a [tape 31, mode 3, rewind]
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[c,9,128] /dev/nst0 [tape 0, mode 0, no rewind]
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....
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[c,9,160] /dev/nst0l [tape 0, mode 1, no rewind]
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....
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[c,9,192] /dev/nst0m [tape 0, mode 2, no rewind]
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....
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[c,9,224] /dev/nst0a [tape 0, mode 3, no rewind]
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....
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[c,9,255] /dev/nst31a [tape 31, mode 3, no rewind]
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The SCSI generic (sg) devices are allocated the char major number of 21.
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There are 256 possible SCSI generic (sg) devices:
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[c,21,0] /dev/sg0
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[c,21,1] /dev/sg1
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....
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[c,21,255] /dev/sg255
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Note that the SCSI generic device name's use of a trailing letter (e.g. /dev
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/sgc) is deprecated.
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Each SCSI disk (but not each partition), each SCSI CD-ROM and each SCSI tape
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is mapped to an sg device. SCSI devices that don't fit into these three
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categories (e.g. scanners) also appear as sg devices.
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Pseudo devices [see Section 10.1] can cause devices that are usually not
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considered as SCSI to appear as SCSI device names. For example an ATAPI
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CD-ROM may be picked up by the ide-scsi pseudo driver and mapped to /dev/scd0
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.
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The linux/Documentation/devices.txt file supplied within the kernel source
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is the definitive reference for Linux device names and their corresponding
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major and minor number allocations.
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-----------------------------------------------------------------------------
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3.3. Device Names in devfs
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The device pseudo file system can be mounted as /dev in which case it
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replaces the traditional Linux device subdirectory. Alternatively it can be
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mounted elsewhere (e.g. /devfs) and supplement the existing device structure.
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Without devfs, devices names are typically maintained in the dev directory
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of the root partition. Hence the device names (and their associated
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permissions) have file system persistence. The existence of a device name
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does not necessarily imply such a device (or even its driver) is present. To
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save users having to create device name entries (with the mknod command) most
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Linux distributions come with thousands of device names defined in the /dev
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directory. When applications try to open() the device name then an errno
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value of ENODEV indicates there is no corresponding device (or driver)
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currently available.
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Devfs takes a different approach in which the existence of the device name
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is directly related to the presence of the corresponding device (and its
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driver).
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Assuming devfs is mounted on /dev then SCSI devices have primary device
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names that might look like this:
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/dev/scsi/host0/bus0/target1/lun0/disc [whole disk]
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/dev/scsi/host0/bus0/target1/lun0/part6 [partition 6]
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/dev/scsi/host0/bus0/target1/lun0/generic [sg device for disk]
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/dev/scsi/host1/bus0/target2/lun0/cd [CD reader or writer]
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/dev/scsi/host1/bus0/target2/lun0/generic [sg device for cd]
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/dev/scsi/host2/bus0/target0/lun0/mt [tape mode 0 rewind]
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/dev/scsi/host2/bus0/target0/lun0/mtan [tape mode 3 no rewind]
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/dev/scsi/host2/bus0/target0/lun0/generic [sg device for tape]
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The sg device on the third line corresponds to the "whole disk" on the first
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line since they have the same SCSI address (i.e. host0/bus0/target1/lun0). If
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the sg driver is a module and it has not yet been loaded (or it has been
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unloaded) then the "generic" device names in the above list will not be
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present.
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[Notice the spelling of "disc" as the devfs author favours English spelling
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over the American variant.] It can be seen that devfs's naming scheme closely
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matches the SCSI addressing discussed in Section 3.1. It is worth noting that
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the IDE subsystem uses a similar devfs device naming scheme with the word
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"scsi" replaced with "ide". Devfs is discussed further in Chapter 12.
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-----------------------------------------------------------------------------
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3.4. Device Names in scsidev
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A utility program called scsidev adds device names to the /dev/scsi
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directory that reflect the SCSI address of each device. The first 2 letters
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of the name are the upper level SCSI driver name (i.e. either sd, sr, st or
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sg). The number following the "h" is the host number while the number
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following the "-" is meant for host identification purposes. For PCI adapters
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this seems to be always 0 while for ISA adapters it is their IO address.
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[Perhaps this field could be made more informative or dropped.] The numbers
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following the "c", "i" and "l" are channel (bus), target id and lun values
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respectively. Raw disks are shown without a trailing partition number while
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partitions contained within them are shown with the partition number
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following a "p".
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The scsidev would typically be run as part of the boot up sequence. It may
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also be useful to run it after the SCSI configuration has changed (e.g.
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adding or removing lower level driver modules, or the use of the add/
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remove-single-device command). After scsidev has been run on my system which
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contains 2 disks, a cd reader and writer plus a scanner, then the following
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names were added in the /dev/scsi directory:
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$ ls -l /dev/scsi/ # abridged
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total 0
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brw------- 8, 0 Sep 2 11:56 sdh0-0c0i0l0
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brw------- 8, 1 Sep 2 11:56 sdh0-0c0i0l0p1
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...
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brw------- 8, 8 Sep 2 11:56 sdh0-0c0i0l0p8
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brw------- 8, 16 Sep 2 11:56 sdh0-0c0i1l0
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brw------- 8, 17 Sep 2 11:56 sdh0-0c0i1l0p1
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...
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brw------- 8, 24 Sep 2 11:56 sdh0-0c0i1l0p8
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crw------- 21, 0 Sep 2 11:56 sgh0-0c0i0l0
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crw------- 21, 1 Sep 2 11:56 sgh0-0c0i1l0
|
||
crw------- 21, 2 Sep 2 11:56 sgh1-0c0i2l0
|
||
crw------- 21, 3 Sep 2 11:56 sgh1-0c0i5l0
|
||
crw------- 21, 4 Sep 2 11:56 sgh1-0c0i6l0
|
||
br-------- 11, 0 Sep 2 11:56 srh1-0c0i2l0
|
||
br-------- 11, 1 Sep 2 11:56 srh1-0c0i6l0
|
||
The mapping between the SCSI generic device names (sg) and their
|
||
corresponding names when controlled by other upper level drivers (i.e. sd, sr
|
||
or st) can be seen by looking for name matches when the second letter is
|
||
ignored. Hence "sdh0-0c0i0l0" and "sgh0-0c0i0l0" refer to the same device. By
|
||
process of elimination the "sgh1-0c0i5l0" filename is the scanner since that
|
||
class of devices can only be accessed via the sg interface.
|
||
|
||
The scsidev package also includes the ability to introduce names like /dev/
|
||
scsi/scanner by manipulating the /etc/scsi.alias configuration file. The
|
||
package also includes the useful rescan-scsi-bus.sh utility. For further
|
||
information about scsidev see W6. On my system, both devfs and scsidev
|
||
co-exist happily.
|
||
-----------------------------------------------------------------------------
|
||
|
||
Chapter 4. Kernel Configuration
|
||
|
||
The Linux kernel configuration is usually found in the kernel source in the
|
||
file: /usr/src/linux/.config . It is not recommended to edit this file
|
||
directly but to use one of these configuration options:
|
||
|
||
<EFBFBD><EFBFBD>*<2A>make config - starts a character based questions and answer session
|
||
|
||
<EFBFBD><EFBFBD>*<2A>make menuconfig - starts a terminal-oriented configuration tool (using
|
||
ncurses)
|
||
|
||
<EFBFBD><EFBFBD>*<2A>make xconfig - starts a X based configuration tool
|
||
|
||
|
||
The descriptions of these selections that is displayed by the associated
|
||
help button can be found in the flat ASCII file: /usr/src/linux/Documentation
|
||
/Configure.help
|
||
|
||
Ultimately these configuration tools edit the .config file. An option will
|
||
either indicate some driver is built into the kernel ("=y") or will be built
|
||
as a module ("=m") or is not selected. The unselected state can either be
|
||
indicated by a line starting with "#" (e.g. "# CONFIG_SCSI is not set") or by
|
||
the absence of the relevant line from the .config file.
|
||
|
||
The 3 states of the main selection option for the SCSI subsystem (which
|
||
actually selects the SCSI mid level driver) follow. Only one of these should
|
||
appear in an actual .config file:
|
||
CONFIG_SCSI=y
|
||
CONFIG_SCSI=m
|
||
# CONFIG_SCSI is not set
|
||
|
||
Some other common SCSI configuration options are:
|
||
CONFIG_BLK_DEV_SD [disk (sd) driver]
|
||
CONFIG_SD_EXTRA_DEVS [extra slots for disks added later]
|
||
CONFIG_BLK_DEV_SR [SCSI cdrom (sr) driver]
|
||
CONFIG_BLK_DEV_SR_VENDOR [allow vendor specific cdrom commands]
|
||
CONFIG_SR_EXTRA_DEVS [extra slots for cdroms added later]
|
||
CONFIG_CHR_DEV_ST [tape (st) driver]
|
||
CONFIG_CHR_DEV_OSST [OnSteam tape (osst) driver]
|
||
CONFIG_CHR_DEV_SG [SCSI generic (sg) driver]
|
||
CONFIG_DEBUG_QUEUES [for debugging multiple queues]
|
||
CONFIG_SCSI_MULTI_LUN [allow probes above lun 0]
|
||
CONFIG_SCSI_CONSTANTS [symbolic decode of SCSI errors]
|
||
CONFIG_SCSI_LOGGING [allow logging to be runtime selected]
|
||
|
||
CONFIG_SCSI_<ll_driver> [numerous lower level adapter drivers]
|
||
CONFIG_SCSI_DEBUG [lower level driver for debugging]
|
||
|
||
CONFIG_SCSI_PPA [older parallel port zip drives]
|
||
CONFIG_SCSI_IMM [newer parallel port zip drives]
|
||
|
||
CONFIG_BLK_DEV_IDESCSI [ide-scsi pseudo adapter]
|
||
CONFIG_I2O_SCSI [scsi command set over i2o bus]
|
||
CONFIG_SCSI_PCMCIA [for SCSI HBAs on PCMCIA bus]
|
||
CONFIG_USB_STORAGE [usb "mass storage" type]
|
||
|
||
CONFIG_MAGIC_SYSRQ [Alt+SysRq+S for emergency sync]
|
||
[Alt+SyrRq+U for emergency remount ro]
|
||
|
||
If the root file system is on a SCSI disk then it makes sense to build into
|
||
the kernel the SCSI mid level, the sd driver and the host adapter driver that
|
||
the disk is connected to. In most cases it is usually safe to build the sr,
|
||
st and sg drivers as modules so that they are loaded as required. If a device
|
||
like a scanner is on a separate adapter then its driver may well be built as
|
||
a module. In this case, that adapter driver will need to be loaded before the
|
||
scanner will be recognized.
|
||
|
||
Linux distributions have many of the SCSI subsystem drivers built as modules
|
||
since building all of them in would lead to a very large kernel that would
|
||
exceed the capabilities of the boot loader. This leads to a "chicken and the
|
||
egg" problem in which the SCSI drivers are needed to load the root file
|
||
system and vice versa. The 2 phase load used by the initrd device addresses
|
||
this problem (see Chapter 6 for more details).
|
||
-----------------------------------------------------------------------------
|
||
|
||
Chapter 5. Boot Parameters
|
||
|
||
On a PC the motherboard's BIOS together with the SCSI BIOS provided by most
|
||
SCSI host adapters takes care of the problem of loading the boot loader's
|
||
image from a SCSI disk into memory and executing it. This may require some
|
||
settings to be changed in the motherboard's BIOS. When more than one SCSI
|
||
adapter is involved, the SCSI BIOS settings may need to change to indicate
|
||
which one contains the disk with the boot image. The boot image make also
|
||
come from an ATA (IDE) disk, a bootable CD-ROM or a floppy.
|
||
|
||
Both lilo and grub are commonly used boot loaders with Linux. Their
|
||
configuration files are in /etc/lilo.conf and /etc/grub.conf [3]
|
||
respectively. One difference is that after changing lilo's configuration the
|
||
lilo command must be executed for the changes to take effect (and there is no
|
||
equivalent requirement for grub). See their "man" pages for usage
|
||
information. An excellent paper on lilo and the Linux bootup sequence can be
|
||
found ftp://icaftp.epfl.ch/pub/people/almesber/booting/bootinglinux-0.ps.gz.
|
||
For further information on grub see www.gnu.org/software/grub.
|
||
|
||
Some boot parameters related to the SCSI subsystem:
|
||
single [enter single user mode]
|
||
<n> [enter run level <n> {0..6}]
|
||
root=/dev/sda6 [*]
|
||
root=/dev/scsi/host0/bus0/target0/lun0/part6 [*]
|
||
root=/dev/sd/c0b0t0u0p6 [*]
|
||
devfs=mount [overrides CONFIG_DEVFS_MOUNT=n]
|
||
devfs=nomount [overrides CONFIG_DEVFS_MOUNT=y]
|
||
init=<command> [executes <command> rather than init]
|
||
quiet [reduce output to console during boot]
|
||
debug [increase output to console during boot]
|
||
nmi_watchdog=0 [turn off NMI watchdog on a SMP machine]
|
||
max_scsi_luns=1 [limits SCSI bus scans to lun==0]
|
||
scsi_allow_ghost_devices=<n>
|
||
* When devfs is in use the initial read-only mount of the root partition can
|
||
be done via the old /dev/sd<a><n> notation or the new devfs notation (and two
|
||
of these are shown). The joint "root=/dev/sda6 single" may be useful when
|
||
disk or adapter changes have broken the kernel boot load.
|
||
|
||
The "root=" argument may also be a hex number. For example, if the root
|
||
partition is on /dev/sda3 then "root=803" is appropriate. The last two digits
|
||
are the minor device number discussed in an earlier section.
|
||
|
||
The default argument to the "init" parameter is /sbin/init (see man (8)
|
||
init). If files such as /etc/fstab have incorrect entries, it may be useful
|
||
to drop directly into a shell with "init=/bin/bash". However if shared
|
||
libraries files or their paths are inappropriate this may also fail. That
|
||
leaves "init=/sbin/sash" which is a statically linked shell with many useful
|
||
commands (for repairing a system) built in (see man (8) sash).
|
||
|
||
When Linux fails to boot after reporting a message like:
|
||
VFS: Cannot open root device 08:02
|
||
then the kernel expected to find a root partition on device /dev/sda2 and did
|
||
not. The numbers in the error message are major and minor device numbers (in
|
||
hex) [see Section 3.2 for the mapping to device names]. In such situations
|
||
the "root" boot option can be useful (also the rdev command can be used to
|
||
modify where the boot image looks for the root partition).
|
||
|
||
Lilo's configuration file /etc/lilo.conf can take the "root=" option in two
|
||
ways. The normal way is a line like: 'root=/dev/sda2'. In this case /dev/sda2
|
||
is converted into major and minor numbers based on the state of the system
|
||
when the lilo command is executed. This can be a nuisance, especially if
|
||
hardware is going to be re-arranged. The other way is a line of the form:
|
||
'append="root=/dev/sda2"' In this case the /dev/sda2 is passed through to the
|
||
kernel the next time it is started. This is the same as giving the "root=/dev
|
||
/sda2" string at the kernel boot time prompt. It is interpreted by the kernel
|
||
at startup (once the HBAs and their attached devices have been recognized)
|
||
and thus is more flexible.
|
||
-----------------------------------------------------------------------------
|
||
|
||
Chapter 6. Modules and their Parameters
|
||
|
||
There are many SCSI related modules. The mid and upper level modules are
|
||
listed below:
|
||
|
||
<EFBFBD><EFBFBD>*<2A>scsi_mod.o
|
||
|
||
<EFBFBD><EFBFBD>*<2A>sd_mod.o
|
||
|
||
<EFBFBD><EFBFBD>*<2A>sr_mod.o
|
||
|
||
<EFBFBD><EFBFBD>*<2A>st.o [osst.o]
|
||
|
||
<EFBFBD><EFBFBD>*<2A>sg.o
|
||
|
||
|
||
Notice that the first 3 have "_mod" appended to their normal driver names.
|
||
Lower level drivers tend to use the name (or an abbreviation) of the HBA's
|
||
manufacturer (e.g. advansys) plus optionally the chip number of the major
|
||
controller chip (e.g. sym53c8xx for symbios controllers based on the NCR
|
||
53c8?? family of chips).
|
||
|
||
All SCSI modules depend on the mid level. This means if the SCSI mid level
|
||
is not built into the kernel and if scsi_mod.o has not already been loaded
|
||
then a command like modprobe st will cause the scsi_mod.o module to be
|
||
loaded. There could well be other dependencies, for example modprobe sr_mod
|
||
will also cause the cdrom module to be loaded if it hasn't been already. Also
|
||
if the SCSI mid level is a module, then all other SCSI subsystem drivers must
|
||
be modules (this is enforced by the kernel build configuration tools).
|
||
|
||
Modules can be loaded with the modprobe <module_name> command which will try
|
||
to load any modules that the nominated <module_name> depends on. Also <
|
||
module_name> does not need the trailing ".o" extension which is assumed if
|
||
not given. The insmod <module_name> command will also try and load <
|
||
module_name> but without first loading modules it depends on. Rules for how
|
||
modules can cause other modules to be loaded (with appropriate parameters
|
||
appended) are usually placed in the file /etc/modules.conf. [Note that in
|
||
earlier Linux kernels this file was often called /etc/conf.modules.] For
|
||
further information about the format of this file try man modules.conf.
|
||
|
||
Any module can have its allowable command line parameters queried with this
|
||
command: modinfo -p <module_name>.
|
||
|
||
When upper level drivers are initialized and if there are no hosts active
|
||
then the mid level will attempt to load a module called "scsi_hostadapter".
|
||
An "alias" can then be used to associate "scsi_hostadapter" with the actual
|
||
name of the lower level (adapter) driver. For example, a line like "alias
|
||
scsi_hostadapter aic7xxx" in the /etc/modules.conf file would cause the
|
||
aic7xxx module to be loaded (if there were no lower level drivers already
|
||
active). [4]
|
||
|
||
There is a special relationship between the module parameter
|
||
"scsi_hostadapter" and the initrd file system. For more information see man
|
||
initrd and man mkinitrd. [5]
|
||
-----------------------------------------------------------------------------
|
||
|
||
Chapter 7. Proc pseudo file system
|
||
|
||
The proc pseudo file system provides some useful information about the SCSI
|
||
subsystem. The kernel configuration option that selects "proc_fs" is
|
||
CONFIG_PROC_FS and in almost all cases it should be selected. SCSI specific
|
||
information is found under the directory /proc/scsi. Probably the most
|
||
commonly accessed entry is cat /proc/scsi/scsi which lists the attached SCSI
|
||
devices. See Section 8.3 for more details.
|
||
|
||
The lower level drivers are allocated proc_fs entries of the form:
|
||
/proc/scsi/<driver_name>/<scsi_adapter_number>
|
||
where the <driver_name> is something like "aic7xxx" or "BusLogic". The <
|
||
scsi_adapter_number> (also known as the host number) is the same number that
|
||
was discussed in Section 3.1. Note that one driver may control one or more
|
||
hosts. What is stored in this file is lower level driver dependent (and in
|
||
the case of some adapter drivers it is possible to set parameters via this
|
||
file). When reporting problems to newsgroups or maintainers it is useful to
|
||
include the output of this file (e.g. cat /proc/scsi/aic7xxx/0 ).
|
||
|
||
The cdrom driver provides information about attached cdrom devices in the /
|
||
proc/sys/dev/cdrom directory. This will include both SCSI devices (i.e. those
|
||
controlled by the sr driver) and IDE devices (i.e. those controlled by the
|
||
ide-cd driver). See Section 9.2.3.
|
||
|
||
The sg driver provides information about its state and attached hosts and
|
||
devices in the /proc/scsi/sg directory. See Section 9.4.3.
|
||
|
||
More general information on the proc pseudo file system can be found in the
|
||
kernel source file: /usr/src/linux/Documentation/filesystems/proc.txt.
|
||
-----------------------------------------------------------------------------
|
||
|
||
Chapter 8. Mid Level, Unifying layer
|
||
|
||
The SCSI mid level is common to all usage of the SCSI subsystem. Probably
|
||
its most important role is to define internal interfaces and services that
|
||
are used by all other SCSI drivers. These internal mechanisms are not
|
||
discussed in this document [see ref: W2].
|
||
|
||
The primary kernel configuration parameter "CONFIG_SCSI" determines whether
|
||
the mid level is built in (when "=y") or a module (when "=m"). If
|
||
"CONFIG_SCSI=m" then all other SCSI subsystem drivers must also be modules.
|
||
|
||
When the mid level is built as a module then it probably never needs to be
|
||
loaded explicitly because using 'modprobe' to load any other SCSI subsystem
|
||
module will cause the mid level to be loaded first (if it is not already).
|
||
|
||
Some upper and lower level drivers do not (fully) load if there are no
|
||
devices for that driver to control. Sometimes the report is loud as in this
|
||
case for the imm driver which controls zip drives connected to a parallel
|
||
port:
|
||
$ modprobe imm
|
||
imm.o: init_module: No such device
|
||
lsmod will not show the "imm" module as loaded. In other cases the result is
|
||
more subtle. For example, if the sg driver is loaded in a system with no
|
||
(real or pseudo) scsi devices then the /proc/scsi/sg directory will not
|
||
appear. [It will be created when the first scsi device is recognized.]
|
||
-----------------------------------------------------------------------------
|
||
|
||
8.1. boot parameters
|
||
|
||
SCSI drivers that are built into the kernel are checked in a pre-determined
|
||
order to see if HBAs that they can control are present. The user has no
|
||
control over this order which in most cases is arbitrary but in the case of
|
||
some older ISA adapters is required to stop misidentification [6] .
|
||
scsi_logging=<n>
|
||
where <n> is 0 to turn logging off
|
||
where <n> is non-zero to turn logging on
|
||
|
||
max_scsi_luns=<n>
|
||
where <n> is a number between 1 and 8 (< lk 2.4.7),
|
||
>= lk 2.4.7 the upper limit can be much larger
|
||
|
||
scsi_allow_ghost_devices=<n>
|
||
where (<n> - 1) is the maximum lu number to ghost if the
|
||
the corresponding device is offline. When <n>==0
|
||
(default) then don't ghost any devices (in lk 2.4.26
|
||
and later)
|
||
|
||
scsihosts=host0:hosts1::host3
|
||
|
||
The recently introduced devfs defines a "scsihosts" boot time parameter to
|
||
give the user some control over this. See the devfs documentation [ref: W5]
|
||
for a description. The host names given in the list to the "scsihosts" boot
|
||
option are the names of lower level drivers (e.g. "scsihosts=advansys:imm::
|
||
ide-scsi"). [7] [8] Devfs does not need to be present for "scsihosts" to be
|
||
used. The "scsihosts" parameter, if given, is echoed during in the boot up
|
||
messages. For example:
|
||
scsi: host order: advansys:imm::ide-scsi
|
||
Also if multiple HBA are present in a system then they are scanned in a fixed
|
||
order (see footnote). The "scsihosts" parameter only effects how these HBAs
|
||
are indexed (i.e. which SCSI adapter numbers are associated with them by the
|
||
kernel). In the above example, if the "imm" driver is not found during boot
|
||
up, then the scsi adapter number "1" is not allocated. If the "imm" driver is
|
||
later loaded as a module, then it will adopt scsi adapter number "1". If a
|
||
driver that is not named in "scsihosts" is found, then it will get the next
|
||
available scsi adapter number (e.g. a built in aic7xxx driver would get scsi
|
||
adapter number "2" in the above example).
|
||
|
||
A full list of kernel parameters with some explanations can be found in the
|
||
file /usr/src/linux/Documentation/kernel-parameters.txt .
|
||
-----------------------------------------------------------------------------
|
||
|
||
8.2. module parameters
|
||
|
||
If SCSI disks are present in the system then it usually is better to build
|
||
the mid level driver into the kernel. However if the SCSI subsystem is only
|
||
being used periodically (e.g. to burn CD-Rs on an ATAPI CD writer) then
|
||
building the mid level as a module is fine. The module load time options are
|
||
the same as the driver's built in options:
|
||
scsi_logging_level=<n>
|
||
where <n> is the logging level mask (0 for logging off)
|
||
max_scsi_luns=<n>
|
||
scsihosts=host0::host2
|
||
scsi_allow_ghost_devices=<n>
|
||
-----------------------------------------------------------------------------
|
||
|
||
8.3. proc interface
|
||
|
||
To display the SCSI devices currently attached (and recognized) by the SCSI
|
||
subsystem use cat /proc/scsi/scsi.
|
||
|
||
The output looks like this:
|
||
Attached devices:
|
||
Host: scsi0 Channel: 00 Id: 02 Lun: 00
|
||
Vendor: PIONEER Model: DVD-ROM DVD-303 Rev: 1.10
|
||
Type: CD-ROM ANSI SCSI revision: 02
|
||
Host: scsi1 Channel: 00 Id: 00 Lun: 00
|
||
Vendor: IBM Model: DNES-309170W Rev: SA30
|
||
Type: Direct-Access ANSI SCSI revision: 03
|
||
|
||
After the "Attached devices:" line there are 3 lines for each recognized
|
||
device. The first of these lines is SCSI address information discussed in
|
||
Section 3.1. The following 2 lines of data are obtained from a INQUIRY
|
||
command that was performed on the device when it was attached. See Section
|
||
9.4 for the relationship between the ordering of these devices compared with
|
||
the sg driver's ordering (which most of the time is the same).
|
||
|
||
Existing devices can be removed using echo "scsi remove-single-device <h>
|
||
<b> <t> <l>" > /proc/scsi/scsi where the variables are host, bus (channel),
|
||
target (scsi id) and lun. The success (or otherwise) of this command can be
|
||
determined by sending a subsequent cat /proc/scsi/scsi command. The removal
|
||
will fail if the device is busy (e.g. if a file system on the device is
|
||
mounted).
|
||
|
||
New devices can be added using echo "scsi add-single-device <h> <b> <t> <l
|
||
>" > /proc/scsi/scsi where the variables are host, bus (channel), target
|
||
(scsi id) and lun. The success (or otherwise) of this command can be
|
||
determined by sending a subsequent cat /proc/scsi/scsi command. [9]
|
||
|
||
The SCSI subsystem does not support hot-plugging of SCSI devices (there may
|
||
also be electrical issues on the associated SCSI parallel bus). It is
|
||
recommended that those who use add+remove-single-device make sure that other
|
||
devices on that SCSI bus are inactive if re-plugging is going to take place.
|
||
|
||
To output a list of internal SCSI command blocks use echo "scsi dump <n>"
|
||
> /proc/scsi/scsi where the numeric value of <n> doesn't matter. This is
|
||
probably only of interest to people chasing down bugs within the SCSI
|
||
subsystem.
|
||
|
||
To start (or stop) logging information being sent to the console/log use
|
||
echo "scsi log <token> <n>" > /proc/scsi/scsi where <token> is one of: {all,
|
||
none, error, timeout, scan, mlqueue, mlcomplete, llqueue, llcomplete,
|
||
hlqueue, hlcomplete, ioctl} and <n> is a number between 0 and 7. The tokens
|
||
"all" and "none" don't take an <n> argument. Prefix meanings:
|
||
hl upper level drivers [exception: sg uses "timeout"]
|
||
ml mid level
|
||
ll lower level drivers
|
||
[adapter drivers often have there own flags]
|
||
The value "0" turns off logging while "7" maximizes the volume of output.
|
||
Logging information will only be output if CONFIG_SCSI_LOGGING was selected
|
||
in the kernel build.
|
||
|
||
Warning Warning: "scsi log all" (and several other variants) can cause a
|
||
logging infinite loop if the log file (typically /var/log/messages )
|
||
lies on a SCSI disk. Either turn off the kernel logging daemon or
|
||
direct its output to a non SCSI device.
|
||
-----------------------------------------------------------------------------
|
||
|
||
Chapter 9. Upper level drivers
|
||
|
||
The upper level drivers maintain the kernel side of the OS interface for the
|
||
logical class of devices they represent (e.g. disks). They are also
|
||
responsible for managing certain kernel and SCSI subsystem resources such as
|
||
kernel memory and SCSI command structures. Applications in the user space
|
||
access these drivers by opening a special file (block or char) typically
|
||
found in the /dev directory tree.
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.1. Disk driver (sd)
|
||
|
||
Two types of SCSI devices are accessible via the sd driver:
|
||
|
||
<EFBFBD><EFBFBD>*<2A>"direct access" devices which are usually magnetic disks. [SCSI
|
||
peripheral device code is 0]
|
||
|
||
<EFBFBD><EFBFBD>*<2A>"Optical memory devices" which are often called MOD disks. [SCSI
|
||
peripheral device code is 7]
|
||
|
||
|
||
The sd driver is a block device which means that it is closely associated
|
||
with the block subsystem. It also supports the concept of partitions. [man sd
|
||
dates from 1992.]
|
||
|
||
The sd driver is capable of recognizing 128 disks when it is loaded at
|
||
kernel boot time or later as a module. However, once it is loaded, it will
|
||
only recognize a fixed number of additional disks. The number of additional
|
||
disks that can be accommodated is set by the kernel configuration parameter
|
||
CONFIG_SD_EXTRA_DEVS whose default value is 40.
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.1.1. sd boot parameters
|
||
|
||
None.
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.1.2. sd module parameters
|
||
|
||
The sd driver takes no parameters when loaded as a module. Note that its
|
||
module name is sd_mod.o.
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.2. CDROM driver (sr or scd)
|
||
|
||
CDROM and DVD drives (and WORM devices) are accessible via the sr upper
|
||
level device driver. While "sr" is the device driver name, "sr_mod" is its
|
||
module name. The device file name is either /dev/sr<n> or /dev/scd<n>.
|
||
|
||
Following is a diagram illustrating the CDROM subsystem of which sr is a
|
||
part:
|
||
|
||
[cdrom]
|
||
|
||
The architecture of the CD-ROM subsystem.
|
||
|
||
This diagram glosses over some of the differences between the protocol
|
||
stacks. CDROM device names are not maintained by the uniform CDROM layer but
|
||
rather by each individual protocol stack. In the case of the SCSI subsystem,
|
||
device names are maintained by the sr driver while the IDE subsystem
|
||
maintains device names with its central "ide" driver (i.e. not by the ide-cd
|
||
driver). USB and IEEE1394 cd devices names are maintained by their respective
|
||
stacks. This may partially explain why the /dev/cdrom is often a symbolic
|
||
link to the appropriate subsystem's device name.
|
||
|
||
Two types of SCSI devices are accessible via the sr driver:
|
||
|
||
<EFBFBD><EFBFBD>*<2A>CD-ROM devices (including DVD players) [SCSI peripheral device code is 5]
|
||
|
||
<EFBFBD><EFBFBD>*<2A>"Write-once read-multiple" devices which are known as WORMs. [SCSI
|
||
peripheral device code is 4]
|
||
|
||
|
||
The sr driver is capable of recognizing 256 CDROM/DVD drives when it is
|
||
loaded at kernel boot time or later as a module. However, once it is loaded,
|
||
it will only recognize a fixed number of additional drives. The number of
|
||
additional drives that can be accommodated is set by the kernel configuration
|
||
parameter CONFIG_SR_EXTRA_DEVS whose default value is 2.
|
||
|
||
People often use the dd command to read a data CDROM containing an iso9660
|
||
file system. If a count argument is not given then the dd command will read
|
||
the number of 2048 byte sectors indicated by the SCSI Read Capacity command.
|
||
Unfortunately this can include unwritten (or "run out") sectors at the end of
|
||
the image that can cause I/O errors. Use the isosize command (see its man
|
||
page) to find the true length of the iso9660 image and use that in the "count
|
||
=" argument given to the dd command.
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.2.1. sr boot parameters
|
||
|
||
None.
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.2.2. sr module parameters
|
||
|
||
Doing a test to find out if a cdrom drive supports XA mode (mode 2) triggers
|
||
firmware bugs on some drives. Consequently the check for XA mode support is
|
||
turned off by default. The following module parameter is provided:
|
||
xa_test=<0|1>
|
||
to override the default. [Currently there seems to be no way to turn on XA
|
||
mode testing when the sr driver is built into the kernel.]
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.2.3. sr proc interface
|
||
|
||
All the following files are readable by all and produce ASCII output when
|
||
read:
|
||
/proc/sys/dev/cdrom/autoclose
|
||
/proc/sys/dev/cdrom/autoeject
|
||
/proc/sys/dev/cdrom/check_media
|
||
/proc/sys/dev/cdrom/debug
|
||
/proc/sys/dev/cdrom/info
|
||
/proc/sys/dev/cdrom/lock
|
||
They reflect the current state of the CDROM subsystem. This location is part
|
||
of the procfs's window through to the sysctl configuration mechanism (see man
|
||
sysctl). All but info are writable by the superuser. There is a column for
|
||
each CDROM and DVD player in the system in info (not just SCSI devices).
|
||
|
||
As an example, the auto eject feature can be turned on by the superuser with
|
||
the command echo "1" > /proc/sys/dev/cdrom/autoeject. This will cause cdroms
|
||
to be ejected from the drive when unmounted.
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.2.4. ATAPI cdroms
|
||
|
||
Many Linux users have no SCSI devices (or adapters) in their systems. They
|
||
become a little perplexed as to why cd writer software (e.g. cdrecord and
|
||
cdrdao) and cd music reading programs (e.g. cdparanoia) use the Linux SCSI
|
||
subsystem. The answer is that these programs need lower level access to these
|
||
devices. ATAPI (ATA Packet Interface) is essentially a SCSI command set sent
|
||
over an ATA [10] transport. [The discussion in this section is also
|
||
applicable to ATAPI tape drives and ATAPI floppy drives.]
|
||
|
||
Currently both cdrecord and cdparanoia interface to the SCSI generic driver
|
||
(sg) and, in the case of ATAPI cd devices, use the ide-scsi pseudo device
|
||
driver to access the hardware. This may change in the future as in the 2.4
|
||
series kernels a packet interface ioctl has been added to the uniform cdrom
|
||
layer (see the diagram in Section 9.2 above). [11]
|
||
|
||
The default action of the IDE subsystem in Linux is to claim all ATA devices
|
||
for its built-in drivers. In the case of an ATAPI cd writer, it will be
|
||
claimed by the built-in ide-cd driver. Once this has happened, the SCSI
|
||
subsystem is unable to get control over an ATAPI device. The ide-scsi (pseudo
|
||
lower level SCSI) driver can only register ATAPI devices in the SCSI
|
||
subsystem that have not already been claimed by the IDE subsystem.
|
||
|
||
Notice the built-in qualification in the previous paragraph. If both the
|
||
ide-cd and ide-scsi drivers are modules then the first one loaded will claim
|
||
the ATAPI cd devices (e.g. cd/dvd readers and writers). Furthermore you can
|
||
switch the controlling driver module by rmmod-ing one and modprobe-ing the
|
||
other.
|
||
|
||
Probably the most flexible way to instruct the IDE core driver that you want
|
||
the cd writer at /dev/hdd accessible to cdrecord is to use the kernel boot
|
||
option: "hdd=ide-scsi". This will cause the ide-cd driver to bypass /dev/hdd
|
||
(irrespective of whether ide-cd driver is built-in or a module). As long as
|
||
the ide-scsi driver is built-in or a module then it will "capture" the cd
|
||
writer at /dev/hdd (with the IDE core driver loading the ide-scsi module if
|
||
required).
|
||
|
||
The ide-cd driver module can be instructed to ignore certain ATA devices
|
||
with the following syntax:
|
||
modprobe ide-cd ignore='hdc hdd'
|
||
In this case the ide-cd driver will ignore the devices at /dev/hdc and /dev/
|
||
hdd . This effect can also be accomplished by placing a line like this:
|
||
"options ide-cd ignore=hdd" in the /etc/modules.conf file.
|
||
|
||
A new option added in the lk 2.4 series is of the form "hdd=scsi". This
|
||
option seems to have a similar function to the "hdd=ide-scsi" option
|
||
discussed above. Furthermore "hdd=scsi" can only be used if both the SCSI
|
||
mid-level and the ide-scsi drivers are built into the kernel (otherwise "BAD
|
||
OPTION" is reported by the ide_setup function).
|
||
|
||
To find out whether an ATAPI cd device is "owned" by the SCSI subsystem, the
|
||
output of cat /proc/scsi/scsi can be checked. Another technique is to observe
|
||
the "drive name:" line of cat /proc/sys/dev/cdrom/info for "sr" entries. The
|
||
following output is from my system:
|
||
$ cat /proc/sys/dev/cdrom/info
|
||
CD-ROM information, Id: cdrom.c 3.12 2000/10/18
|
||
|
||
drive name: sr1 sr0
|
||
drive speed: 16 0
|
||
drive # of slots: 1 1
|
||
Can close tray: 1 1
|
||
Can open tray: 1 1
|
||
Can lock tray: 1 1
|
||
Can change speed: 1 1
|
||
Can select disk: 0 0
|
||
Can read multisession: 1 1
|
||
Can read MCN: 1 1
|
||
Reports media changed: 1 1
|
||
Can play audio: 1 1
|
||
Can write CD-R: 1 0
|
||
Can write CD-RW: 1 0
|
||
Can read DVD: 0 1
|
||
Can write DVD-R: 0 0
|
||
Can write DVD-RAM: 0 0
|
||
|
||
Once an ATAPI cd writer at /dev/hdd has been registered by the SCSI
|
||
subsystem, then cdroms should be mounted via the "scd" device name and cd
|
||
players should also use the "scd" device. Strangely the hdparm command should
|
||
still use the /dev/hdd device file (or the "echo ... > /proc/ide/hdd/
|
||
settings" method described in this section). [12]
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.3. Tape driver (st)
|
||
|
||
The tape driver interface is documented in the file /usr/src/linux/drivers/
|
||
scsi/README.st and on the st(4) man page (type man st). The file README.st
|
||
also documents the different parameters and options of the driver together
|
||
with the basic mechanisms used in the driver.
|
||
|
||
The tape driver is usually accessed via the mt command (see man mt). mtx is
|
||
an associated program for controlling tape autoloaders (see
|
||
mtx.sourceforge.net).
|
||
|
||
The st driver detects those SCSI devices whose peripheral device type is
|
||
"Sequential-access" (code number 1) unless they appear on the driver's
|
||
"reject_list". [Currently the OnStream tape drives (described in a following
|
||
section) are the only entry in this reject_list.]
|
||
|
||
The st driver is capable of recognizing 32 tape drives. There are 8 device
|
||
file names for each tape drive: a rewind and non-rewind variant for each of 4
|
||
modes (numbered 0 to 3). See the tape device file name examples in Section
|
||
3.2 on device names. Any number of tape drives (up to the overall limit of
|
||
32) can be added after the st driver is loaded.
|
||
|
||
ATAPI tape drives can be controlled by this driver with help from the
|
||
ide-scsi pseudo adapter driver. The discussion in Section 9.2.4 also applies
|
||
for ATAPI tape drives (and ATAPI floppies).
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.3.1. st boot parameters
|
||
|
||
|
||
st=xxx[,yyy] where xxx is one of the following:
|
||
buffer_kbs:<n>
|
||
write_threshold_kbs:<n>
|
||
max_buffers:<n>
|
||
max_sg_segs:<n>
|
||
|
||
(The old boot parameters st=aa[,bb[,cc[,dd]]] supported but deprecated)
|
||
|
||
The default driver buffer size (buffer_kbs) is 32 (i.e. 32 KB). The default
|
||
asynchronous write threshold (write_threshold_kbs) is 30 (i.e. 30 KB). The
|
||
default number of buffers allocated at initialization (max_buffers) is 4. The
|
||
default number of scatter/gather segments to use (max_sg_segs) is 32.
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.3.2. st module parameters
|
||
|
||
|
||
buffer_kbs=<n>
|
||
write_threshold_kbs=<n>
|
||
max_buffers=<n>
|
||
max_sg_segs=<n>
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.3.3. st proc interface
|
||
|
||
None.
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.3.4. osst driver for OnStream devices
|
||
|
||
There is an auxiliary tape driver for tape drives manufactured by OnStream.
|
||
It is an additional upper level driver and can co-exist with the st driver.
|
||
Its driver name is "osst" (as is its module name).
|
||
|
||
The OnStream SC-x0 SCSI tape drives can not be driven by the standard st
|
||
driver, but instead need this special osst driver and use the /dev/osst<x>
|
||
char device nodes (major 206). [Where <x> follows the same naming scheme as
|
||
st devices outlined in Section 3.2.] Via usb-storage and ide-scsi, you may be
|
||
able to drive the USB-x0 and DI-x0 drives as well. Note that there is also a
|
||
second generation of OnStream tape drives (ADR-x0) that supports the standard
|
||
SCSI-2 commands for tapes (QIC-157) and can be driven by the standard driver
|
||
st. For more information, you may have a look at the kernel source file /usr/
|
||
src/linux/drivers/scsi/README.osst. More info on the OnStream driver may be
|
||
found on linux1.onstream.nl/test/.
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.4. Generic driver (sg)
|
||
|
||
All types of SCSI devices are accessible via the sg driver. This means
|
||
devices such as CDROM drives can be accessed both via the sr and sg drivers.
|
||
Other SCSI devices such as scanners can only be accessed via the sg driver.
|
||
The sg driver is capable of recognizing 256 SCSI devices. Any number of
|
||
devices (up to the overall limit of 256) can be added after the sg driver is
|
||
loaded.
|
||
|
||
See reference W4 for the SCSI Generic (sg) driver documentation (also found
|
||
there is the sg_utils package). For SCSI standards see reference W1 and for a
|
||
book on the subject of SCSI programming and pass through mechanisms see
|
||
reference B3.
|
||
|
||
The sg driver in lk 2.4 is "version 3" which adds an additional interface
|
||
structure and some new ioctl()s. The most interesting new ioctl() is SG_IO
|
||
which sends a SCSI command and waits for its response. See the Linux
|
||
Documentation Project site: www.tldp.org/HOWTO/SCSI-Generic-HOWTO/ for a
|
||
full description of the sg driver. A (possibly later) version of this
|
||
document can be found at www.torque.net/sg/p/sg_v3_ho.html.
|
||
|
||
The abbreviation "sg" is used within the kernel to refer both to the SCSI
|
||
generic driver and the scatter-gather capability offered by many modern IO
|
||
devices (usually associated with DMA). The context usually makes it clear
|
||
which one is being referred to. As an example, note the contorted sg ioctl()
|
||
named SG_GET_SG_TABLESIZE where the second "SG" refers to scatter gather.
|
||
|
||
The public interface for sg is found in the file: /usr/src/linux/include/
|
||
scsi/sg.h. Depending on the distribution this may or may not contain the same
|
||
information as /usr/include/scsi/sg.h which is controlled by the GNU library
|
||
maintainers. If these 2 files are not the same use the former header file.
|
||
Those writing applications based on sg should see its documentation for more
|
||
on this matter.
|
||
|
||
The sg driver registers all SCSI devices (with a current maximum of 256) as
|
||
they are seen. Each newly registered SCSI device gets allocated the next
|
||
available minor device number. At least initially this will be the same
|
||
sequence that devices are displayed in mid level's cat /proc/scsi/scsi. The
|
||
sg devices device mapping can be seen with cat /proc/scsi/sg/devices or cat
|
||
/proc/scsi/sg/device_strs. Differences between cat /proc/scsi/scsi and sg
|
||
orderings will appear when a low level driver is removed (e.g. rmmod aha1542)
|
||
or when a device is removed with remove-single-device. The sg driver will
|
||
leave remaining SCSI device mapping to minor device numbers unchanged. This
|
||
potentially leaves a "hole" in the sg mapping. An example follows:
|
||
$ cat /proc/scsi/scsi
|
||
Attached devices:
|
||
Host: scsi0 Channel: 00 Id: 00 Lun: 00
|
||
Vendor: IBM Model: DNES-309170W Rev: SA30
|
||
Type: Direct-Access ANSI SCSI revision: 03
|
||
Host: scsi1 Channel: 00 Id: 02 Lun: 00
|
||
Vendor: PIONEER Model: DVD-ROM DVD-303 Rev: 1.10
|
||
Type: CD-ROM ANSI SCSI revision: 02
|
||
Host: scsi1 Channel: 00 Id: 06 Lun: 00
|
||
Vendor: YAMAHA Model: CRW4416S Rev: 1.0g
|
||
Type: CD-ROM ANSI SCSI revision: 02
|
||
|
||
$ cat /proc/scsi/sg/device_strs
|
||
IBM DNES-309170W SA30
|
||
PIONEER DVD-ROM DVD-303 1.10
|
||
YAMAHA CRW4416S 1.0g
|
||
|
||
$ echo "scsi remove-single-device 1 0 2 0" > /proc/scsi/scsi
|
||
|
||
$ cat /proc/scsi/scsi
|
||
Attached devices:
|
||
Host: scsi0 Channel: 00 Id: 00 Lun: 00
|
||
Vendor: IBM Model: DNES-309170W Rev: SA30
|
||
Type: Direct-Access ANSI SCSI revision: 03
|
||
Host: scsi1 Channel: 00 Id: 06 Lun: 00
|
||
Vendor: YAMAHA Model: CRW4416S Rev: 1.0g
|
||
Type: CD-ROM ANSI SCSI revision: 02
|
||
|
||
$ cat /proc/scsi/sg/device_strs
|
||
IBM DNES-309170W SA30
|
||
<no active device>
|
||
YAMAHA CRW4416S 1.0g
|
||
Notice how the sg driver maintains the row positions of the remaining devices
|
||
in the "device_strs" output. So when the Pioneer dvd player is removed, a
|
||
hole opens up in the sg device mapping which is not reflected in the cat /
|
||
proc/scsi/scsi output. That "hole" corresponds to the device name /dev/sg1.
|
||
|
||
The new sg_io_hdr interface includes a data transfer residual count field
|
||
called "resid". Only some lower level adapters support this feature and those
|
||
that don't always yield zero in this field. At the time of writing the
|
||
advansys, aha152x and the sym53c8xx drivers support this feature.
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.4.1. sg boot parameters
|
||
|
||
The sg driver maintains a reserved buffer for each open file descriptor. The
|
||
purpose is to guarantee applications that data transfers up to the size of
|
||
the reserved buffer will not fail for lack of kernel memory. This is
|
||
important for applications like cdrecord that cannot easily recover (the CDR)
|
||
from a ENOMEM error.
|
||
|
||
In the absence of the boot parameter 'sg_def_reserved_size' or the sg module
|
||
parameter 'def_reserved_size', then each time a sg file descriptor is opened
|
||
the reserved buffer size is inherited from SG_DEF_RESERVED_SIZE which is
|
||
defined in include/linux/sg.h.
|
||
|
||
The SG_DEF_RESERVED_SIZE define value can be overridden by this kernel boot
|
||
option:
|
||
sg_def_reserved_size=<n>
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.4.2. sg module parameters
|
||
|
||
When the sg module is loaded the SG_DEF_RESERVED_SIZE define value can be
|
||
overridden by supplying this option:
|
||
def_reserved_size=<n>
|
||
-----------------------------------------------------------------------------
|
||
|
||
9.4.3. sg proc interface
|
||
|
||
All the following files are readable by all and produce ASCII output when
|
||
read. The file 'def_reserved_size' is also writable by root. The ASCII output
|
||
has been formatted in such a way as to be human and machine readable (and
|
||
hence a compromise). Use Unix commands of the form cat device_hdrs devices to
|
||
see the output of tables.
|
||
/proc/scsi/sg/debug [internal state of sg driver]
|
||
/proc/scsi/sg/def_reserved_size
|
||
[like boot/module load parameter]
|
||
/proc/scsi/sg/devices [table of numeric device data]
|
||
/proc/scsi/sg/device_hdr [column headers for sg/devices]
|
||
/proc/scsi/sg/device_strs [table of strings from INQUIRY]
|
||
/proc/scsi/sg/hosts [table of numeric host data]
|
||
/proc/scsi/sg/host_hdr [column headers for sg/hosts]
|
||
/proc/scsi/sg/host_strs [table of string ids for hosts]
|
||
/proc/scsi/sg/version [sg version number and date]
|
||
All the above files are owned by root and readable by all while
|
||
def_reserved_size is writable by root. For the devices and device_strs files
|
||
the first row output corresponds to /dev/sg0 (sg minor device number 0). The
|
||
second row output corresponds to /dev/sg1, etc. For the hosts and host_strs
|
||
files the first row output corresponds to host (adapter number) 0, etc. For
|
||
numeric tables a missing device or host is indicated by a row of "-1" values.
|
||
For string tables a missing device or host is indicated by a row containing "
|
||
<no active device/host>".
|
||
-----------------------------------------------------------------------------
|
||
|
||
Chapter 10. Lower Level drivers
|
||
|
||
There are too many SCSI low level drivers to detail in this document. As an
|
||
alternative to giving any superficial overview here, the reader is given
|
||
suggestions of places to look for further information.
|
||
|
||
The source directory for the SCSI subsystem in the Linux kernel is a good
|
||
place to start: /usr/src/linux/drivers/scsi. Several drivers have information
|
||
in a "readme" file: README.<driver_name> . Others have extensive information
|
||
at the top of their ".c" file This information often includes a version
|
||
number, change logs and kernel boot time and module load time options. Often
|
||
the latter information can be found in the installation guides of the various
|
||
Linux distributions. Sometimes the driver maintainer will have a web site
|
||
containing the most recent bug fix information. Official maintainers are
|
||
listed in the /usr/src/linux/MAINTAINERS file. If there is nothing there,
|
||
look in the relevant ".c" file in the SCSI subsystem directory. Some old
|
||
drivers have no active maintainers. In such cases posting to the linux-scsi
|
||
newsgroup may help [see N1 ].
|
||
|
||
For an overview of the drivers supplied with the kernel source tree, use one
|
||
of the kernel configuration programs (e.g. cd /usr/src/linux; make menuconfig
|
||
). The help information associated with each selection can be found together
|
||
in one (large) flat file at /usr/src/linux/Documentation/Configure.help.
|
||
Drivers can be obtained from other places. It is unlikely that a SCSI driver
|
||
made for the lk 2.2 series (or before) will build or operate successfully in
|
||
the lk 2.4 series. [From a programmatic viewpoint there are not a lot of
|
||
things that need changing.] Drivers may even be only available in binary
|
||
form, in which case make sure that you trust the provider and follow their
|
||
instructions closely.
|
||
|
||
Lower level drivers can support either of 2 error handling strategies. The
|
||
older one is considered obsolete while the newer one is often called
|
||
"new_eh". The advantage of "new_eh" is that it uses a separate kernel thread
|
||
per host (named "scsi_eh_<n>" where <n> is the host number) to facilitate
|
||
error recovery. Both error handling strategies were also available in the lk
|
||
2.2 series in which very few adapter drivers used "new_eh". In the lk 2.4
|
||
series, more drivers are using it and the plan for the forthcoming lk 2.5
|
||
development series is to drop mid level support for the older, obsolete error
|
||
strategy.
|
||
|
||
Drew Eckhardt's SCSI-HOWTO document [see reference W7 ] goes into much more
|
||
detail about lower level (adapter) drivers than this document. Since that
|
||
SCSI-HOWTO is 5 years old, many things have changed and more drivers have
|
||
been added.
|
||
|
||
There is a lower level driver called scsi_debug that simulates one or more
|
||
"direct access" devices (i.e. disk(s)) using the computer's memory. From lk
|
||
2.4.17 it acts as a "ram disk". While there are many ram disk implementations
|
||
available in Linux (e.g. ramfs), scsi_debug may help to isolate a defective
|
||
scsi driver in a problematic installation. See scsi_debug.c for further
|
||
information.
|
||
-----------------------------------------------------------------------------
|
||
|
||
10.1. Pseudo drivers
|
||
|
||
SCSI can be viewed as a command set and a set of hardware buses that convey
|
||
that command set. Those hardware buses can be further divided into those used
|
||
exclusively for SCSI (e.g. ultra wide), those shared with other protocols
|
||
(e.g. USB, IEEE 1394) and those buses not defined by the various SCSI
|
||
standards. In the final category there are several interesting examples
|
||
including ATAPI CD writers and PC parallel bus ZIP drives. Such devices use
|
||
the SCSI command set (or something very close to it) over a foreign bus.
|
||
|
||
This section briefly outlines various pseudo lower level drivers which
|
||
essentially communicate with other Linux subsystems in order to send the SCSI
|
||
command set to devices controlled by those other subsystems. This raises some
|
||
ownership issues that often confuse users and result in many questions to the
|
||
maintainers.
|
||
|
||
IDE-SCSI. From configuration point of view, ide-scsi will grab and try to
|
||
control every ATA (a.k.a. IDE) device which doesn't have a "native" driver
|
||
attached (such as ide-cd, ide-tape, etc). So for example, if both ide-cd and
|
||
ide-scsi are compiled into the kernel in a system which has an ATAPI cdrom,
|
||
ide-cd will get to control it. If only ide-scsi is compiled in, it will get
|
||
the device. There are some kernel boot time parameters to control which
|
||
driver gets which device.
|
||
|
||
The preferences of the IDE subsystem can be overridden with one of these
|
||
kernel boot time parameters (of which the first is most interesting for this
|
||
subsystem):
|
||
|
||
<EFBFBD><EFBFBD>*<2A> hdx=ide-scsi
|
||
|
||
<EFBFBD><EFBFBD>*<2A> hdx=ide-cdrom
|
||
|
||
<EFBFBD><EFBFBD>*<2A> hdx=ide-floppy
|
||
|
||
|
||
[The term hdx is used to refer to one of the IDE/ATA devices in {hda, hdb,
|
||
hdc ...}.] In the 2.4 series "hdx=scsi" was added but it is not very useful,
|
||
see see Section 9.2.4.
|
||
|
||
When the driver is running, the device will be accessible using the SCSI
|
||
device (/dev/sda, /dev/sr0 , etc), and not through the corresponding /dev/
|
||
hdx device. Still, the /dev/hdx device will be available, but only for
|
||
configuration.
|
||
|
||
All the generic IDE configuration parameters (DMA on/off, 32-bit I/O,
|
||
unmasking irq's, etc) are available by using the /dev/hdx device, for
|
||
example to enable DMA:
|
||
hdparm -d1 /dev/hdx
|
||
[13] Using cat /proc/ide/hdx/settings will show the available settings. All
|
||
the generic IDE driver settings will be available there, as well as the
|
||
following "ide-scsi specific" settings:
|
||
|
||
<EFBFBD><EFBFBD>*<2A>bios_cyl
|
||
|
||
<EFBFBD><EFBFBD>*<2A>bios_head
|
||
|
||
<EFBFBD><EFBFBD>*<2A>bios_sect
|
||
|
||
<EFBFBD><EFBFBD>*<2A>transform
|
||
|
||
<EFBFBD><EFBFBD>*<2A>log
|
||
|
||
|
||
The first three choose the virtual geometry that the drive will return to the
|
||
sd driver, in case it's a disk drive (ZIP, etc). "transform" will configure/
|
||
enable/disable the SCSI to ATAPI CDB transformation layer:
|
||
|
||
<EFBFBD><EFBFBD>*<2A>bit 0: Enable(1)/Disable(0) transformation for commands not originated
|
||
from the sg driver.
|
||
|
||
<EFBFBD><EFBFBD>*<2A>bit 1: Enable/Disable transformation for commands issued using the sg
|
||
driver.
|
||
|
||
|
||
"log" will log debugging information. This is useful also to debug user-space
|
||
programs using the sg driver, as it will list the CDB traffic on the bus --
|
||
each issued command, along with its completion status. To enable/disable a
|
||
specific settings, use something like:
|
||
echo "log:1" > /proc/ide/hdx/settings
|
||
To turn off the "using_dma" flag use:
|
||
echo "using_dma:0" > /proc/ide/hdx/settings
|
||
|
||
PPA + IMM. Iomega ZIP drives come in a variety of flavours including parallel
|
||
port, SCSI, and ATAPI. The parallel port versions (both old and new) are
|
||
driven by ppa and imm respectively.
|
||
|
||
The parallel port ZIP drives are actually SCSI devices which tunnel SCSI
|
||
commands over the parallel port using interfaces called VPI0 (older-style)
|
||
and VPI2 (newer-style). The ppa driver is the VPI0 host implementation and
|
||
the imm driver is the VPI2 host implementation.
|
||
|
||
The way it works is that the HBA is a chip inside the ZIP drive, so that the
|
||
host adapter and the peripheral are in the same actual case.
|
||
|
||
PPSCSI. The new, not-yet-integrated, architecture for devices that use SCSI
|
||
over a parallel port cable is ppscsi. The ppscsi module provides the boiler
|
||
plate code and makes it easy to write implementations for different
|
||
interfaces.
|
||
|
||
Each ppscsi protocol module registers itself with the ppscsi module, passing
|
||
in a list of entry points for the various things that are common to all
|
||
protocol drivers.
|
||
|
||
[ppscsi]
|
||
|
||
The structure of the PPSCSI drivers.
|
||
|
||
The plan is that the ppscsi architecture will absorb both the ppa and imm
|
||
drivers and protocol modules; only vpi0 has been written so far. See
|
||
www.torque.net/parport/ppscsi.html.
|
||
|
||
USB. USB classifies a group of devices as "mass storage" (e.g. disks) and
|
||
interacts with these using the SCSI command set. The module name is
|
||
"usb-storage". See www.one-eyed-alien.net/~mdharm/linux-usb.
|
||
|
||
There is also the usb/microtek driver for controlling X6 USB scanners from
|
||
Microtek. When configured, the SANE application uses the sg driver to send
|
||
SCSI commands over USB to control this scanner.
|
||
|
||
I2O. See kernel source file /usr/src/linux/drivers/i2o/io2_scsi.c .
|
||
|
||
IEEE 1394. Support for IEEE 1394 devices that use the SBP-2 protocol is now
|
||
available (lk 2.4.7). See the IEEE 1394 paragraph in this section for more
|
||
information.
|
||
|
||
iSCSI. An IETF draft is taking shape for iSCSI. This sends the SCSI command
|
||
set over a TCP network connection. iSCSI seems to be gaining popularity
|
||
quickly and there are several implementations for Linux taking shape. One
|
||
implementation is at sourceforge.net/projects/intel-iscsi/. Use your
|
||
favourite search engine to find other projects.
|
||
-----------------------------------------------------------------------------
|
||
|
||
Chapter 11. Raw devices
|
||
|
||
A raw device can be bound to an existing block device (e.g. a disk) and be
|
||
used to perform "raw" IO with that existing block device. Such "raw" IO
|
||
bypasses the caching that is normally associated with block devices. Hence a
|
||
raw device offers a more "direct" route to the physical device and allows an
|
||
application more control over the timing of IO to that physical device. This
|
||
makes raw devices suitable for complex applications like Database Management
|
||
Systems that typically do their own caching.
|
||
|
||
Raw devices are character devices (major number 162). The first minor number
|
||
(i.e. 0) is reserved as a control interface and is usually found at /dev/
|
||
rawctl. A utility called raw (see man raw) can be used to bind a raw device
|
||
to an existing block device. These "existing block devices" may be disks or
|
||
cdroms/dvds whose underlying interface can be anything supported by Linux
|
||
(e.g. IDE/ATA or SCSI).
|
||
|
||
A sequence of commands listing the raw devices and then binding a SCSI disk
|
||
partition followed by binding the whole disk looks like this on my system:
|
||
$ ls -lR /dev/raw*
|
||
crw-r--r-- 1 root root 162, 0 Dec 6 06:54 /dev/rawctl
|
||
|
||
/dev/raw:
|
||
total 0
|
||
crw-r--r-- 1 root root 162, 1 Dec 6 06:54 raw1
|
||
crw-r--r-- 1 root root 162, 2 Dec 6 06:54 raw2
|
||
crw-r--r-- 1 root root 162, 3 Dec 6 06:54 raw3
|
||
crw-r--r-- 1 root root 162, 4 Dec 6 06:54 raw4
|
||
$
|
||
$ raw -qa
|
||
$
|
||
$ raw /dev/raw/raw1 /dev/sda3
|
||
/dev/raw/raw1: bound to major 8, minor 3
|
||
$ raw /dev/raw/raw2 /dev/sda
|
||
/dev/raw/raw2: bound to major 8, minor 0
|
||
$ raw -qa
|
||
/dev/raw/raw1: bound to major 8, minor 3
|
||
/dev/raw/raw2: bound to major 8, minor 0
|
||
|
||
The normal array of system calls for character devices are available on raw
|
||
devices. The size of the transfer for read(2) and write(2) must be an
|
||
integral multiple of the physical device's block size. For a disk this will
|
||
be its sector size which is normally 512 bytes. The data buffer given to read
|
||
() and write() system calls must be aligned to the block size. The lseek(2)
|
||
call needs to align its file read/write offset to a block boundary as well.
|
||
The pread(3) call (see man pread) combines a read() and an lseek() and can be
|
||
useful with raw devices (ditto with pwrite() ). Care should be taken with
|
||
offsets greater than 2 GB (or perhaps 4 GB) on 32 bit architectures where the
|
||
"off_t" type is 32 bits long. One solution is to use the _llseek() call (see
|
||
man llseek).
|
||
|
||
Unix utilities such as recent versions of dd and lmdd (from the lmbench
|
||
suite of programs) can be used to move data to and from "raw" devices as they
|
||
meet the above-mentioned block alignment requirements. Recent versions of the
|
||
sg_dd command in the sg_utils package can access both raw and sg devices.
|
||
|
||
Also note that if the physical device has an odd number of sectors (as shown
|
||
by blockdev --getsize /dev/raw/raw*), the last sector will not be accessible
|
||
using raw IO.
|
||
|
||
Warning If a block device is being accessed via a bound raw device and also
|
||
via its normal block interface then there is no cache coherency
|
||
between the two access mechanisms. For example if /dev/sda1 was both
|
||
mounted and being accessed via a bound raw device then there could be
|
||
data inconsistencies.
|
||
-----------------------------------------------------------------------------
|
||
|
||
Chapter 12. Devfs pseudo file system
|
||
|
||
The main documentation for devfs can be found at: reference W5. The devfs
|
||
name conventions for the SCSI subsystem are outlined in Section 3.3. Devfs is
|
||
selected by the kernel build option CONFIG_DEVFS_FS and whether it is mounted
|
||
at boot time (as /dev) or not is controlled by the kernel build option
|
||
CONFIG_DEVFS_MOUNT. The latter option can be overridden by the kernel boot
|
||
time options "devfs=mount" or "devfs=nomount", whichever is appropriate.
|
||
|
||
The devfs SCSI node names with their default permissions are:
|
||
disc rw------- whole disk including mbr
|
||
part1 rw------- first partition {...p1}
|
||
...
|
||
part15 rw------- 15th partition {...p15}
|
||
cd rw-rw-rw- cd or dvd devices
|
||
mt rw-rw-rw- tape mode 0 with rewind {...m0}
|
||
mtl rw-rw-rw- tape mode 1 with rewind {...m1}
|
||
mtm rw-rw-rw- tape mode 2 with rewind {...m2}
|
||
mta rw-rw-rw- tape mode 3 with rewind {...m3}
|
||
mtn rw-rw-rw- tape mode 0 with no rewind {...m0n}
|
||
mtln rw-rw-rw- tape mode 1 with no rewind {...m1n}
|
||
mtmn rw-rw-rw- tape mode 2 with no rewind {...m2n}
|
||
mtan rw-rw-rw- tape mode 3 with no rewind {...m3n}
|
||
generic rw-r-----
|
||
|
||
These node names are only present if the corresponding device (or
|
||
sub-entities of the device (e.g. partitions)) and driver are present. For
|
||
example if there is no sg driver present then there is no "generic" device
|
||
name. The strings that appear above in braces are appended to the abridged
|
||
"c0b0t0u0" notations outlined below as appropriate.
|
||
|
||
The devfs file names that are block or character special files will be
|
||
called the primary device names in this description. The devfs daemon, called
|
||
devfsd, introduces many symbolic links to those primary device names. This is
|
||
done both for backward compatibility and convenience. These symbolic links
|
||
will be called secondary device names.
|
||
|
||
The secondary device names are controlled by the devfsd configuration file
|
||
usually found in /etc/devfsd.conf . Following is a list of secondary device
|
||
names when the default devfsd.conf file is used:
|
||
Secondary name slink to this primary device name
|
||
--------------------------------------------------------------
|
||
/dev/sda /dev/scsi/host0/bus0/target2/lun0/disc
|
||
/dev/sda1 /dev/scsi/host0/bus0/target2/lun0/part1
|
||
/dev/sd/c0b0t2u0 /dev/scsi/host0/bus0/target2/lun0/disc
|
||
/dev/sd/c0b0t2u0p1 /dev/scsi/host0/bus0/target2/lun0/part1
|
||
/dev/sr0 /dev/scsi/host0/bus0/target4/lun0/cd
|
||
/dev/sr/c0b0t4u0 /dev/scsi/host0/bus0/target4/lun0/cd
|
||
/dev/st0 /dev/scsi/host1/bus0/target0/lun0/mt
|
||
/dev/nst0a /dev/scsi/host1/bus0/target0/lun0/mtan
|
||
/dev/st/c1b0t0u0m0 /dev/scsi/host1/bus0/target0/lun0/mt
|
||
/dev/st/c1b0t0u0m3n /dev/scsi/host1/bus0/target0/lun0/mtan
|
||
/dev/sg0 /dev/scsi/host0/bus0/target2/lun0/generic
|
||
/dev/sg1 /dev/scsi/host0/bus0/target4/lun0/generic
|
||
/dev/sg2 /dev/scsi/host1/bus0/target0/lun0/generic
|
||
/dev/sg/c0b0t2u0 /dev/scsi/host0/bus0/target2/lun0/generic
|
||
/dev/sg/c0b0t4u0 /dev/scsi/host0/bus0/target4/lun0/generic
|
||
/dev/sg/c1b0t0u0 /dev/scsi/host1/bus0/target0/lun0/generic
|
||
|
||
Note that the more common /dev/scd0 variant for SCSI cdroms is not
|
||
supported. There are also /dev/discs, /dev/cdroms and /dev/tapes directories
|
||
that contain symbolic links to all devices (i.e. not just SCSI devices) that
|
||
fall into that categorization:
|
||
Secondary name slink to this primary device
|
||
------------------------------------------------------------
|
||
/dev/discs/disc0 /dev/ide/host0/bus0/target0/lun0 *
|
||
/dev/discs/disc1 /dev/scsi/host0/bus0/target2/lun0 *
|
||
/dev/cdroms/cdrom0 /dev/ide/host0/bus1/target1/lun0/cd
|
||
/dev/cdroms/cdrom1 /dev/scsi/host0/bus0/target4/lun0/cd
|
||
/dev/tapes/tape0 /dev/scsi/host1/bus0/target0/lun0 *
|
||
|
||
Those entries marked with "*" are directories containing the primary
|
||
devices. Note that IDE/ATA devices are listed before SCSI devices. These
|
||
secondary device names mimic the same persistence rules as the primary device
|
||
names. So when a SCSI device (?), or its lower level driver or its upper
|
||
level driver are removed then so are the primary and secondary device names
|
||
associated with it.
|
||
|
||
When devfs is mounted as /dev, the old "/dev/sda6" type can still be used in
|
||
some contexts. This may be convenient if typing is required at the kernel
|
||
boot time prompt. For example if a user wants to change the root partition on
|
||
a "devfs" machine then any of the following examples may be used as a kernel
|
||
boot time option:
|
||
root=/dev/sda6
|
||
root=/dev/scsi/host0/bus0/target0/lun0/part6
|
||
root=/dev/sd/c0b0t0u0p6
|
||
|
||
There are many device scanning programs that expect to see the pre-devfs
|
||
device names present and it will some time before they become devfs aware.
|
||
Also some programs rely on a open of /dev/sg0 (for example) to load the sg
|
||
driver (assuming it is a module and not already loaded). This can be arranged
|
||
by an entry in /etc/devfsd.conf file of:
|
||
LOOKUP sg.* MODLOAD
|
||
and the following in /etc/modules.devfs :
|
||
probeall /dev/sg scsi-hosts sg
|
||
alias /dev/sg* /dev/sg
|
||
|
||
The sg device permissions can be changed with this entry in the /etc/
|
||
devfsd.conf file:
|
||
REGISTER scsi/host.*/bus.*/target.*/lun.*/generic
|
||
PERMISSIONS 0.0 rw-rw-rw-
|
||
See "man devfsd" for more information.
|
||
|
||
An application can determine whether devfs is active by the presence or
|
||
otherwise of the file /dev/.devfsd.
|
||
|
||
A feature of a /dev directory based on a persistent file system (e.g. ext2)
|
||
is the ability to associate permissions with a device file name and keep them
|
||
from one boot to the next. As noted above the default action of devfs is to
|
||
assign device file name permissions anew each time a machine is booted. The
|
||
PERMISSIONS action in the /etc/devfsd.conf can be used to assert permissions
|
||
but this may be considered a little awkward. The devfs document (W5)
|
||
describes a method for getting the best of both worlds. This technique relies
|
||
on the recently added feature in lk 2.4 to mount the same file system at
|
||
multiple points.
|
||
-----------------------------------------------------------------------------
|
||
|
||
Appendix A. Common bus types (SCSI and other)
|
||
|
||
A very good overview of the various bus types touched on in this appendix
|
||
(both SCSI and others) can be found at www.pctechguide.com/04disk2.htm.
|
||
|
||
SCSI. The original SCSI 1 standard (ANSI specification X3.131-1986)
|
||
introduced an 8 bit parallel bus that was able to do asynchronous transfers
|
||
at 1.5 MegaBytes/sec and synchronous transfers up to 5 MB/sec. SCSI commands
|
||
are sent at the asynchronous rate. SCSI data is transferred either at the
|
||
asynchronous rate (worst case) or a negotiated synchronous rate (with 5 MB/
|
||
sec being the best case).
|
||
|
||
FAST SCSI. The SCSI 2 standard raised the maximum synchronous speed to 10 MB/
|
||
sec. SCSI 2 defined several parallel buses: single ended (as used by SCSI 1)
|
||
and a new differential bus. The differential bus has better noise immunity
|
||
and its maximum bus length is 25 metres (compared with single ended's 6
|
||
metres). Tagged queuing of commands was also added by SCSI 2.
|
||
|
||
WIDE SCSI. The SCSI 2 standard also increased the width of the bus allowing
|
||
16 and 32 bit "wide" variants. Very little use has been made of the 32 bit
|
||
width so "wide" usually refers to a 16 bit wide data path. The maximum number
|
||
of SCSI devices that can connect to a parallel SCSI bus is directly related
|
||
to the bus width hence "wide" buses allow a maximum of 16 SCSI devices to be
|
||
connected. [At least one of those devices must be the SCSI "initiator" which
|
||
is usually a host adapter.]
|
||
|
||
ULTRA SCSI. Traditionally synchronous buses are clocked either on the rising
|
||
or falling edge of the clock (which is normally a square wave). A recent
|
||
trend has been to clock on both edges and thus double the available
|
||
bandwidth. This is how ULTRA SCSI doubles the SCSI 2 "fast" speed to 20 MB/
|
||
sec.
|
||
|
||
ULTRA WIDE SCSI. The same "ultra" technique applied to a (16 bit) wide SCSI
|
||
parallel bus yields a bandwidth of 40 MB/sec.
|
||
|
||
ULTRA 2 WIDE SCSI. This variant introduces a new "low voltage" differential
|
||
signalling (LVD) that allows the synchronous clock speed to be doubled
|
||
yielding 80 MB/sec when using a (16 bit) wide bus. In this case the maximum
|
||
SCSI bus length is 12 metres. To be backward compatible with ULTRA WIDE this
|
||
variant can fall back to "single ended" operation. This leads to the
|
||
abbreviation LVD/SE being used by adapter manufacturers. One shortcoming of
|
||
this approach is that the presence of one UW device on a U2W bus will cause
|
||
all other U2W devices to communicate at the slower (i.e. UW) rate. Some
|
||
adapters overcome this by having separate LVD and SE physical buses on the
|
||
same logical SCSI bus.
|
||
|
||
ULTRA 160 SCSI. ULTRA 160 doubles parallel SCSI bus bandwidth yet again. It
|
||
uses a 16 bit wide data path, LVD signalling (see previous entry) and double
|
||
transition clocking that increases the maximum synchronous bandwidth to 160
|
||
MB/sec. Additional features include cyclic redundancy codes (CRC) to improve
|
||
data integrity (compared with a parity bit) and domain validation which
|
||
adjusts transfer rates if the error rate is too high.
|
||
|
||
ULTRA 320 SCSI. Shortly ULTRA 320 adapters will be available (disks with that
|
||
interface are already on the market). This is also a 16 bit wide LVD bus that
|
||
can fall back to slower speeds for compatibility with older devices. It
|
||
extends the features of Ultra 160 by doubling the clock speed. Packetized
|
||
SCSI which sends commands and status at full bus speed (rather than 5 MB/sec)
|
||
is included. Other improvements include "quick arbitration and selection",
|
||
"read and write data streaming" and CRC protection for command blocks as well
|
||
as data (Ultra 160 had CRC protection for data only). Note that adapter cards
|
||
using 64 bit PCI (or better: PCI-X) are required to stop the PCI bus being a
|
||
bottleneck at these speeds. More information can be found at www.scsita.org.
|
||
Recently an Ultra 320 HBA vendor claimed up to 105,000 IO operations per
|
||
second which implies per command SCSI bus overhead is less than 10
|
||
microseconds. There is a draft ULTRA 640 standard but that may be overtaken
|
||
by Serial Attached SCSI.
|
||
|
||
Serial Attached SCSI (SAS). Serial Attached SCSI (SAS) uses the same
|
||
transport technology as Serial ATA (sATA) and extends it. [sATA is described
|
||
below.] SAS can use external expanders to control up to 16000 devices from a
|
||
single HBA. The data transfer is full duplex and 1.5 Gbps or 3.0 Gbps "phys"s
|
||
can be aggregated to increase bandwidth. Cable lengths can be up to 6 meters.
|
||
SAS disks are dual ported. sATA disks can be connected to a SAS expanders
|
||
(but SAS disks can't be connected to a sATA HBA). SAS was demonstrated at
|
||
CeBit recently but won't reach the market until 2004.
|
||
|
||
FC-AL. This stands for Fibre Channel - Arbitrated Loop and may involve dual 2
|
||
Gigabit per second single mode fibre optic links spanning 10 kilometres with
|
||
throughput of up to 400 MegaBytes per second. Often associated with storage
|
||
area networks (SANs). Up to 126 devices can be attached to a loop which in
|
||
turn can be extended to 16 million devices in public loop mode. The
|
||
transmission medium isn't necessarily fibre optic cable: copper (in the form
|
||
of co-axial cable) can also be used at lower speeds and for shorter
|
||
distances.
|
||
|
||
SRP/InfiniBand. SRP (SCSI RDMA Protocol) [ SRP_draft] is a SCSI transport for
|
||
InfiniBand [ Infiniband_trade_association], a high-performance interconnect
|
||
running at 10 and 30 Gbps. SRP driver source is available at
|
||
infiniband.sourceforge.net/Storage/SRP .
|
||
|
||
IEEE 1394. This standard also goes by the name of "Fire Wire" [trademarked by
|
||
Apple] and "iLink" [trademarked by Sony]. It is a serial bus that can run at
|
||
up to 400 Megabits/sec (IEEE 1394a). A newer standard, IEEE 1394b, ups this
|
||
to 800 Megabits/sec (with extensions to 1.6 and 3.2 Gigabits/sec) with cable
|
||
runs up to 100 metres. It has a similar but more general architecture than
|
||
USB. The IEEE 1394 standard allows for the SCSI command set to be carried
|
||
over a 1394 bus. There is a "sbp2" driver now available for the Linux IEEE
|
||
1394 stack. This sbp2 driver is also a SCSI subsystem lower level driver (so
|
||
it is functionally similar to the ide-scsi driver). So IEEE 1394 devices that
|
||
use the SBP-2 protocol (e.g. disks, cd-rw/dvd drives, MO drives and scanners)
|
||
can be accessed via the SCSI subsystem. See Linux1394.sourceforge.net for
|
||
more information. The sbp2 driver is now in lk 2.4.7 .
|
||
|
||
iSCSI. This is a new IETF standard for sending the SCSI command set over a
|
||
TCP connection (or several of them). This permits SCSI devices (targets such
|
||
as disks) to be network appliances, accessed locally (or potentially at a
|
||
great distance) by a host machine.
|
||
|
||
NON SCSI buses. The following buses are not defined by the SCSI standards but
|
||
are of interest because they either can carry the SCSI command set, are in
|
||
some way related to the Linux SCSI subsystem or supply a similar
|
||
functionality to SCSI products.
|
||
|
||
IDE/ATA (ATAPI). IDE is the most used disk type on PC systems today. The
|
||
acronym stands for Integrated Drive Electronics and as the name suggests it
|
||
places the bulk of the IO "intelligence" on the disk controller card rather
|
||
than spreading it between the device (most often a disk) and a controller
|
||
(HBA) as SCSI does. IDE grew out of the ST506 and ESDI standards in the
|
||
1980s. EIDE (extended IDE) is a related acronym. The modern standards that
|
||
refer to this bus architecture are known as ATA and can be found at
|
||
www.t13.org. The ATA Packet Interface (ATAPI) extends the disk oriented
|
||
command set to support CDROM and tape drives. The ATAPI command set closely
|
||
resembles the SCSI command set. The most recent ATA technology is outlined in
|
||
the next paragraph.
|
||
|
||
ATA 133. The ATA standards used by IDE devices have also been marching
|
||
through the adjectives (e.g. fast and ultra) and the numbers (e.g. 2, 33, 66,
|
||
100 and 133). The most recent addition is ATA 133 which supports burst rates
|
||
of 133 MB/sec and up to 2 devices per bus. [PCs typically have 2 and often 4
|
||
ATA buses.] ATA 66, 100 and 133 need a special cable. ATA cables are
|
||
relatively short precluding IDE devices being external to the computer. Cable
|
||
lengths have previously been limited to 18 inches although 1 metre long
|
||
cables have now appeared. Coincidently 133 MB/sec in also the maximum
|
||
throughput of the normal PCI bus found in most PCs. The are higher speed (and
|
||
wider) versions of PCI but they are relatively rare.
|
||
|
||
Serial ATA (sATA). Serial ATA uses 2 differential pairs to exchange data with
|
||
a sATA disk less than 1 metre away at 1.5 Gigabits per second. One pair takes
|
||
data to the disk and the other returns data from the disk. Data rates up to
|
||
150 Megabytes per second are possible (data transfer is half duplex). sATA is
|
||
a point to point connection, not a bus, so ATA's master and slave strapping
|
||
disappears. sATA cabling is less bulky and the form factor of its plugs and
|
||
sockets are smaller than parallel ATA (and the SCSI Parallel interface). sATA
|
||
devices are beginning to appear on the market. sATA-2 is a draft standard
|
||
that doubles the serial data rate to 3 Gigabits per second.
|
||
|
||
USB. Universal Serial Bus (USB) has a bandwidth of between 1.5 and 12
|
||
Megabits/sec (the latter speed with USB 1.1). Up to 127 devices can be
|
||
connected using a series of hubs each of which connects up to 7 devices (with
|
||
a 5 metre limit). USB supplies 5 volts at 0.5 amps to power small devices.
|
||
USB is "plug and play", hot pluggable and supports isochronous data transfers
|
||
(required for audio and video devices that need guaranteed minimum
|
||
bandwidth).
|
||
|
||
PC Parallel port. The original PC parallel port was uni-directional (towards
|
||
the printer) and was capable of about 10 KB/sec. The IEEE 1284 standard in
|
||
1994 introduced 5 modes of data transfer:
|
||
|
||
<EFBFBD><EFBFBD>*<2A>Compatibility mode (forward direction)
|
||
|
||
<EFBFBD><EFBFBD>*<2A>Nibble mode (reverse direction)
|
||
|
||
<EFBFBD><EFBFBD>*<2A>Byte mode (reverse direction)
|
||
|
||
<EFBFBD><EFBFBD>*<2A>EPP mode (bi-directional)
|
||
|
||
<EFBFBD><EFBFBD>*<2A>ECP mode (bi-directional)
|
||
|
||
|
||
Enhanced Parallel Port (EPP) achieves transfer speeds of between 500 KB/sec
|
||
and 2 MB/sec and is targeted at CD-ROMs, tapes and hard drives. Extended
|
||
Capability Port (ECP) includes run length encoding and support for DMA. ECP
|
||
is targeted at fast printers and scanners.
|
||
|
||
I2O. "The I2O (Intelligent Input/Output) specification defines a standard
|
||
architecture for intelligent I/O that is independent of both the specific
|
||
device being controlled and the host operating system (OS)" [from
|
||
www.i2osig.org]. It defines a "split driver" model in which the OS Services
|
||
Module (OSM) sits between the host OS device interface and the I2O
|
||
communications layer while the Hardware Device Module (HDM) sits between the
|
||
I2O communications layer and the hardware. The HDM may well run on a
|
||
dedicated processor (IOP).
|
||
-----------------------------------------------------------------------------
|
||
|
||
Appendix B. Changes between lk 2.2 and (during) 2.4
|
||
|
||
Significant work has been done to change the single SCSI command queue used
|
||
in lk 2.2 to one command queue per device. To make the SCSI subsystem more
|
||
SMP friendly the granularity of the locks is much finer grained. In lk 2.2
|
||
the whole subsystem essentially used one lock.
|
||
|
||
Even though it is not part of the SCSI subsystem, the inclusion of devfs
|
||
solves many SCSI device addressing problems that existed in the past.
|
||
Associated with devfs but very useful even in its absence is the "scsihosts"
|
||
kernel boot time (and module load time) option. This option allows users to
|
||
have some control over the ordering of multiple SCSI hosts.
|
||
|
||
This appendix is difficult to maintain since features and drivers that have
|
||
proven useful in lk 2.4 (and its development tree) have tended to be back
|
||
ported into the higher release numbers of the lk 2.2 series.
|
||
|
||
Currently (lk 2.4.2) support for MO devices is broken. Old DOS file systems
|
||
with a block size of 2048 bytes also have been reported as broken. The
|
||
problem seems to arise with media that have a physical block size larger than
|
||
the 1 KB logical block size used by the block subsystem. Only the sd driver
|
||
has this problem (luckily not the sr driver in which 2048 byte sectors are
|
||
the norm).
|
||
-----------------------------------------------------------------------------
|
||
|
||
B.1. Mid level changes
|
||
|
||
|
||
SCSI_IOCTL_GET_IDLUN {ioctl, changed}
|
||
-----------------------------------------------------------------------------
|
||
|
||
B.2. sd changes
|
||
|
||
|
||
HDIO_GETGEO_BIG {ioctl, new}
|
||
|
||
-----------------------------------------------------------------------------
|
||
|
||
B.3. sr changes
|
||
|
||
No sr changes reported. As a related matter, the "hdx=scsi" kernel boot
|
||
option has been added. See Section 9.2.4 for more details.
|
||
-----------------------------------------------------------------------------
|
||
|
||
B.4. st changes
|
||
|
||
No interface changes. In lk 2.2 the maximum number of extra tape devices
|
||
that could be added after boot time was limited to 3. This limitation has
|
||
been removed (leaving a maximum of 32 tape devices as noted earlier).
|
||
|
||
A variant st driver called "osst" to handle early model OnStream tape drives
|
||
has been added in lk 2.4 .
|
||
-----------------------------------------------------------------------------
|
||
|
||
B.5. sg changes
|
||
|
||
The main change is the addition of a new interface structure called
|
||
"sg_io_hdr". The existing interface structure (called "sg_header") was found
|
||
to be inflexible requiring the concatenation of raw data together with
|
||
meta-data in the read() and write() commands.
|
||
sg_io_hdr {new interface structure}
|
||
SG_IO {new ioctl}
|
||
direct IO {present but commented out, see ALLOW_DIO}
|
||
procfs output {new information in /proc/scsi/sg directory}
|
||
boot/module parameters {new}
|
||
|
||
Up to 64 bytes of sense data can be obtained from the sg_io_hdr interface
|
||
structure. Also a residual count associated with the data transfer is
|
||
available (if the lower level driver supports it, if not the residual count
|
||
will be 0).
|
||
-----------------------------------------------------------------------------
|
||
|
||
B.6. Changes during the lk 2.4 series
|
||
|
||
Even though the lk 2.4 production series is meant to be "stable" there have
|
||
been a significant number of changes as well as bug fixes. The following list
|
||
does not include changes to the lower level (adapter) drivers. Each item of
|
||
the list is prefixed by the kernel version that it was introduced. [14]
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.4] added the SCSI_IOCTL_GET_PCI ioctl(),
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.7] the "lun" bits (3 bits representing lun values 0 through 7 in
|
||
the SCSI 1 and SCSI 2 standards) are no longer masked into the second
|
||
byte of SCSI commands if the INQUIRY for that devices shows a SCSI level
|
||
greater than SCSI_2,
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.7] the max_scsi_luns kernel (and module scsi_mod) option previously
|
||
could be 1 to 7. Now the upper value can be large. [The scan algorithms
|
||
are still doing a sequential scan rather than using REPORT_LUNS.]
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.7] both scsi_unregister_host() and scsi_unregister_module() now
|
||
return an int (previously they were void functions). They return 0 for
|
||
success, -1 for failure (typically busy),
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.7] the upper level drivers now report the correct scsi device name
|
||
when they are attached. [The log messages that started with "Detected
|
||
..." previously sometimes reported the wrong device (e.g. sdc rather than
|
||
sdb).] Kernel boot up messages will now show SCSI devices as "Attached
|
||
...",
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.7] 'max_sectors' was added to the Scsi_Host structure,
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.8] some mid level logic was altered to retry commands if the sense
|
||
buffer indicates that logical unit is becoming ready [ASC=4, ASQ=1],
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.9] a major st update,
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.9] mid level changed to retry commands if lower level (adapter)
|
||
driver returned DID_RESET,
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.10] original result (including SCSI status) saved when mid level
|
||
issues a REQUEST SENSE so it can be restored afterwards,
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.10] added BLKGETSIZE64, BLKBSZSET and BLKBSZGET ioctls to sd + sr,
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.10] sg update that fixes generic_unplug_device() race + bumps
|
||
access_count on opens (and decrements on releases),
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.11] added MODULE_LICENSE macro in most drivers, mostly
|
||
MODULE_LICENSE("GPL"),
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.11] scsi_pid bumped for each command (why?),
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.11] st update to bump access_count. Now all upper level drivers
|
||
increment access_count on opens and decrement it on releases,
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.13] scatterlist structure grows (alt_address is removed, page and
|
||
offset added),
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.13] don't probe luns > 7 for target <= SCSI_2 ,
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.14] fine tuning (bug fixes) associated with scatterlist structure
|
||
changes [it broke st ?],
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.15] 16 byte SCSI commands permitted [MAX_COMMAND_SIZE changes from
|
||
12 to 16]. HBA driver must set Scsi_Host::max_cmd_len to 16 for mid level
|
||
to forward 16 byte SCSI commands,
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.15] BLKGETSIZE + BLKGETSIZE64 ioctl() implementations moved out of
|
||
SCSI subsystem (and into block subsystem),
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.15] large st update,
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.15] lk 2.5.0 forks off so lk2.4.15==lk2.5.0 .
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.17] add generic_unplug_device() call to scsi_wait_req(). This stops
|
||
long waits in SCSI_IOCTL_SEND_COMMAND.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.17] fix device scanning bug where, in some cases, the scsi_level
|
||
(i.e. SCSI standard adherence) was misplaced.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.17] major sg driver update, add mmap()-ed IO
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.18] permit upper level driver "init()" functions (e.g. sd_init() )
|
||
to fail gracefully. [Add Scsi_Device::detected and scsi_unregister_module
|
||
() .]
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.18] Fix for clustering (SCSI commands) on MO devices.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.18] st driver update (compression algorithms).
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.18] update Documentation/scsi.txt and scsi-generic.txt .
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.18] Revamp scsi_debug driver .
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.19] Scsi reservation and reset capability added. Reservations allow
|
||
multiple machines to share the same device (via a reserve/release
|
||
mechanism). Scsi reset (via sg) is needed to "break" a reservation held
|
||
by a non-responding machine.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.19] Introduce BLIST_LARGELUN to handle LUNs larger than 7 despite
|
||
reporting SCSI 2.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.19] Change sd and sr so RECOVERED_ERROR is not treated as a hard
|
||
error. Send warning to log/console.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.19] Zero out sg's buffers before use. [Sg version upgraded from
|
||
3.1.22 to 3.1.24 but this is not reflected in sg.h (supeficial).]
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.20] Support for highmem I/O added. Used by aic7xxx, 3w-xxxx, esp,
|
||
megaraid, qlogicfc and sym53c8xx_2 LLDs.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.20] "blocking_open" boot time, module load time parameter added to
|
||
st.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.21] Give new HBAs a new host number (higher than any previously
|
||
used) unless there is a "scsihosts" match. Host numbering sequence
|
||
"holes" are only re-used if there is a "scsihosts" match.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.21] stop the SCSI status RECOVERED ERROR being treated as an error
|
||
by the mid level (complements a change in 2.4.19).
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.21] use the TEST_UNIT_READY command (rather than START_STOP) to
|
||
determine if removable media has changed (in sd driver).
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.21] major work on ide-scsi driver.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.21] add aic79xx driver for Adaptec Ultra 320 controllers.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.22] Extend timeout of SEND DIAGNOSTIC command to 2 hours. This is
|
||
for foreground extended self tests.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.26] Add 'scsi_allow_ghost_devices' kernel boot time and scsi_mod
|
||
module option.
|
||
|
||
<EFBFBD><EFBFBD>*<2A> [2.4.27] SATA support via "libata" library introduced. SATA disks appear
|
||
with SCSI subsystem names (e.g. "/dev/sdb) and respond to SCSI commands
|
||
(via a command translation facility).
|
||
|
||
|
||
-----------------------------------------------------------------------------
|
||
Appendix C. Troubleshooting
|
||
|
||
Many SCSI problems are caused by cabling and (lack of, or inappropriate)
|
||
termination. This often results in repeated SCSI bus resets, parity or CRC
|
||
errors and sometimes reduced transfer speeds. There is a good SCSI
|
||
termination tutorial at this site: [http://www.scsita.org/aboutscsi/
|
||
SCSI_Termination_Tutorial.html] www.scsita.org/aboutscsi/
|
||
SCSI_Termination_Tutorial.html. There is other useful SCSI information at
|
||
that site (see W9).
|
||
|
||
There is also a SCSI "faq" site (see W10) that addresses many configuration
|
||
and troubleshooting issues. Although the main focus of this site is Windows
|
||
(and its ASPI interface), much is relevant to SCSI in Linux and other Unix
|
||
implementations.
|
||
|
||
When it looks like something has partially locked up the system, the ps
|
||
command can be useful for finding out what may be causing the problem. The
|
||
following options may be useful for identifying what part of the kernel may
|
||
be causing the problem. This information could be forwarded to the
|
||
maintainers.
|
||
ps -eo cmd,wchan
|
||
ps -eo fname,tty,pid,stat,pcpu,wchan
|
||
ps -eo pid,stat,pcpu,nwchan,wchan=WIDE-WCHAN-COLUMN -o args
|
||
The most interesting option for finding the location of the "hang" is
|
||
"wchan". If this is a kernel address then ps will use /proc/ksyms to find the
|
||
nearest symbolic location. The "nwchan" option outputs the numerical address
|
||
of the "hang".
|
||
|
||
If the system is not responding to keystrokes, then <Alt+ScrollLock> in text
|
||
mode should output a stack trace while <Ctrl+ScrollLock> should output a list
|
||
of all processes. If the log is still working, the output will be sent there
|
||
as well as appearing on the console.
|
||
|
||
If the kernel has been built with the CONFIG_MAGIC_SYSRQ, then in text mode
|
||
<Alt+SysRq+H> will list available commands. Of these <Alt+SysRq+S> is useful
|
||
for doing an emergency sync while <Alt+SysRq+U> will remount file systems in
|
||
read only mode. After that <Alt+SysRq+B> to reboot the machine might be your
|
||
next move.
|
||
-----------------------------------------------------------------------------
|
||
|
||
Appendix D. Performance, Test and Debugging tools
|
||
|
||
scu. The SCSI Command Utility (SCU) implements various SCSI commands
|
||
necessary for normal maintenance and diagnostics of SCSI peripherals. Some of
|
||
its features include: formatting, scanning for (and reassigning) bad blocks,
|
||
downloading new firmware, executing diagnostics and obtaining performance
|
||
information. It is available on several Unix platforms (and NT), however it
|
||
is only currently available in binary form. See [http://www.bit-net.com/
|
||
~rmiller/scu.html] www.bit-net.com/~rmiller/scu.html for more details.
|
||
|
||
dd. Very useful for testing the streaming performance of disks and cdroms/
|
||
dvds. See man dd for more details. Here is an example for timing how long a
|
||
disk takes to read 1 GB (10**9 bytes) starting from block 0:
|
||
$ time dd if=/dev/sda of=/dev/null bs=512 count=1953126
|
||
If the raw device /dev/raw/raw1 is bound to /dev/sda then the above line is
|
||
equivalent to:
|
||
$ time dd if=/dev/raw/raw1 of=/dev/null bs=512 count=1953126
|
||
This may be slower than expected since one 512 byte sector is being read at a
|
||
time. Changing the last 2 arguments to "bs=8k count=122071" should give
|
||
better timings for the "raw" dd.
|
||
|
||
dt. The Data Test (DT) program is modelled on dd's syntax but dt can do a lot
|
||
more than sequential copies. It is a comprehensive data test program for SCSI
|
||
devices such as disks, tapes and cdrom/dvds. It is available on several Unix
|
||
platforms (and NT), and its source is available (unlike its stable mate "scu"
|
||
discussed earlier). See [http://www.bit-net.com/~rmiller/dt.html]
|
||
www.bit-net.com/~rmiller/dt.html for more details.
|
||
|
||
lmdd. This command is part of the lmbench suite of programs and is a variant
|
||
of the dd command. It has been tailored for IO measurements and outputs
|
||
timing and throughput numbers on completion. Hence the time command and a
|
||
calculator are not needed.
|
||
|
||
blockdev. Fetches the sector size, the number of sectors and read ahead
|
||
status of a block device (typically a disk). Can also be used to flush
|
||
buffers and reread the partition table. See man blockdev.
|
||
|
||
sg_dd. This command is part of the sg_utils package (see W4) and is another
|
||
variant of the dd command in which either the input and/or output file is a
|
||
sg or a raw device. The block size argument ("bs") must match that of the
|
||
physical device in question. The "skip" and "seek" arguments can be up to 2**
|
||
31 - 1 on a 32 bit architecture allowing 1TB disks to be accessed (2G * 512).
|
||
The Linux system command llseek() is used to seek with a 64 bit file read/
|
||
write offset. The lmdd does not handle the > 2GB case and the dd command gets
|
||
creative with multiple relative seeks. sg_dd has a "bpt" (blocks per
|
||
transfer) argument that controls the number of blocks read or written in each
|
||
IO transaction.
|
||
|
||
There are other programs in the sg_utils package to scan the SCSI bus (
|
||
sg_scan and sg_map), to measure SCSI bus throughput (sg_rbuf and sg_turs ),
|
||
show data from the SCSI inquiry command (sg_inq) and spin up (or down) media
|
||
(sg_start).
|
||
|
||
dd_rescue + scsiinfo. This dd variant is designed to rescue damaged media
|
||
such as SCSI (or IDE) disks and CDROMs (see W6). The scsiinfo utility for
|
||
displaying and changing mode page information is also at that site.
|
||
|
||
sard. This utility is modelled on System V Release 4's sar -d for producing
|
||
IO statistics for mounted devices and partitions. It has been developed by
|
||
Stephen Tweedie and includes the sard utility and a required kernel patch
|
||
which expands the output of /proc/partitions . It can be found at [ftp://
|
||
ftp.uk.linux.org/pub/linux/sct/fs/profiling] ftp.uk.linux.org/pub/linux/sct/
|
||
fs/profiling. It collects statistics at a relatively low level (e.g. SCSI mid
|
||
level) compared to programs like vmstat (see "man vmstat").
|
||
-----------------------------------------------------------------------------
|
||
|
||
Appendix E. Compile options and System calls including ioctls
|
||
|
||
The compile options in this appendix are those which a system administrator
|
||
might conceivably want to change. Naturally the defaults are chosen so the
|
||
vast majority of users will not need to modify anything. In some cases
|
||
setting kernel build time options, kernel boot time parameters or module load
|
||
parameters has the same effect as changing a driver compile time option.
|
||
|
||
System calls act as the interface between application programs and the
|
||
kernel and its drivers. In the case of the layered driver architecture that
|
||
the SCSI subsystem uses, the upper layer drivers handle most of the system
|
||
calls.
|
||
|
||
The SCSI subsystem has a "bubble down" ioctl structure. First the upper
|
||
level driver associated with the open file descriptor attempts to decode the
|
||
ioctl. If it doesn't recognize it then the ioctl is passed down to the mid
|
||
level. If the mid level doesn't recognize it then the ioctl is passed down to
|
||
the lower level driver associated with the file descriptor. If the lower
|
||
level driver doesn't recognize it then a EINVAL error is generated.
|
||
|
||
Some ioctls are dispatched to related subsystems.
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.1. Mid level
|
||
|
||
The following header files in the kernel source are relevant to the mid
|
||
level:
|
||
/usr/src/linux/include/scsi/scsi.h
|
||
/usr/src/linux/include/scsi/scsi_ioctl.h
|
||
|
||
These files are meant for applications to use (other than parts in a
|
||
__KERNEL__ conditional compilation block). They may also be found in /usr/
|
||
include/scsi directory but it is best not to trust these versions as they are
|
||
maintained with the glibc library and may lag the kernel version being used.
|
||
Usually in Linux systems /usr/include/linux can be relied upon to be a
|
||
symbolic link to the kernel source's include area (typically /usr/src/linux/
|
||
include/linux). This symbolic link can be used to include the correct
|
||
scsi_ioctl.h using the following trick: #include <linux/../scsi/scsi_ioctl.h
|
||
>
|
||
|
||
This include file: /usr/src/linux/drivers/scsi/scsi.h is the key internal
|
||
header file for the SCSI subsystem. As such it will not be discussed here
|
||
other than to point out it has the same file name (but it's in a different
|
||
directory) as the include file mentioned at the beginning of this section.
|
||
This sometimes causes confusion.
|
||
|
||
The mid level drivers/scsi/scsi_scan.c file maintains an array of known SCSI
|
||
devices with idiosyncrasies . [This was known as the "black list" but that
|
||
was considered to judgmental.] The array is called "device_list". The various
|
||
value are:
|
||
|
||
<EFBFBD><EFBFBD>*<2A>BLIST_NOLUN only probe lun 0
|
||
|
||
<EFBFBD><EFBFBD>*<2A>BLIST_FORCELUN force all 8 luns to be probed
|
||
|
||
<EFBFBD><EFBFBD>*<2A>BLIST_BORKEN passes through broken flag to lower level driver
|
||
|
||
<EFBFBD><EFBFBD>*<2A>BLIST_KEY sends magical MODE SENSE (pc=0x2e) to unlock device
|
||
|
||
<EFBFBD><EFBFBD>*<2A>BLIST_SINGLELUN only allow IO on one lun at a time
|
||
|
||
<EFBFBD><EFBFBD>*<2A>BLIST_NOTQ disable tagged queuing
|
||
|
||
<EFBFBD><EFBFBD>*<2A>BLIST_SPARSELUN keep going after lun not found
|
||
|
||
<EFBFBD><EFBFBD>*<2A>BLIST_MAX5LUN only probe up to lun 5
|
||
|
||
<EFBFBD><EFBFBD>*<2A>BLIST_ISDISK override INQUIRY's type with disk (direct access) type
|
||
|
||
<EFBFBD><EFBFBD>*<2A>BLIST_ISROM override INQUIRY's type with ROM
|
||
|
||
|
||
-----------------------------------------------------------------------------
|
||
E.1.1. Mid level compile options
|
||
|
||
None.
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.1.2. Mid level ioctls
|
||
|
||
See the following files:
|
||
/usr/src/linux/include/scsi/scsi.h
|
||
|
||
Note that the SCSI status constants defined in include/scsi/scsi.h are
|
||
shifted 1 bit right from the values in the SCSI standards:
|
||
scsi.h constant value SCSI 2 standard value
|
||
----------------------------------------------------
|
||
CHECK_CONDITION 0x1 0x2
|
||
CHECK_GOOD 0x2 0x4
|
||
BUSY 0x4 0x8
|
||
....
|
||
|
||
Summary of ioctl()s follow:
|
||
SCSI_IOCTL_SEND_COMMAND
|
||
This interface is deprecated - users should use
|
||
the scsi generic (sg) interface instead, as this
|
||
is a more flexible approach to performing
|
||
generic SCSI commands on a device.
|
||
|
||
The structure that we are passed should look like:
|
||
|
||
struct sdata {
|
||
unsigned int inlen; [i] Length of data written to device
|
||
unsigned int outlen; [i] Length of data read from device
|
||
unsigned char cmd[x]; [i] SCSI command (6 <= x <= 16)
|
||
[o] Data read from device starts here
|
||
[o] On error, sense buffer starts here
|
||
unsigned char wdata[y]; [i] Data written to device starts here
|
||
};
|
||
Notes:
|
||
- The SCSI command length is determined by examining
|
||
the 1st byte of the given command. There is no way
|
||
to override this.
|
||
- Data transfers are limited to PAGE_SIZE (4K on
|
||
i386, 8K on alpha).
|
||
- The length (x + y) must be at least OMAX_SB_LEN
|
||
bytes long to accommodate the sense buffer when
|
||
an error occurs. The sense buffer is truncated to
|
||
OMAX_SB_LEN (16) bytes so that old code will not
|
||
be surprised.
|
||
- If a Unix error occurs (e.g. ENOMEM) then the user
|
||
will receive a negative return and the Unix error
|
||
code in 'errno'. If the SCSI command succeeds then
|
||
0 is returned. Positive numbers returned are the
|
||
compacted SCSI error codes (4 bytes in one int)
|
||
where the lowest byte is the SCSI status. See the
|
||
drivers/scsi/scsi.h file for more information on this.
|
||
|
||
SCSI_IOCTL_GET_IDLUN
|
||
This ioctl takes a pointer to a "struct scsi_idlun" object
|
||
as its third argument. The "struct scsi_idlun" definition
|
||
is found in <scsi/scsi.h>. It gets populated with scsi
|
||
host, channel, device id and lun data for the given device.
|
||
Unfortunately that header file "hides" that structure
|
||
behind a "#ifdef __KERNEL__" block. To use this, that
|
||
structure needs to be replicated in the user's program.
|
||
Something like:
|
||
typedef struct my_scsi_idlun {
|
||
int four_in_one; /* 4 separate bytes of info
|
||
compacted into 1 int */
|
||
int host_unique_id; /* distinguishes adapter cards from
|
||
same supplier */
|
||
} My_scsi_idlun;
|
||
"four_in_one" is made up as follows:
|
||
(scsi_device_id | (lun << 8) | (channel << 16) |
|
||
(host << 24))
|
||
These 4 components are assumed (or masked) to be 1 byte each.
|
||
|
||
SCSI_IOCTL_GET_BUS_NUMBER
|
||
In lk 2.2 and earlier this ioctl was needed to get the
|
||
host number. During lk 2.3 development the
|
||
SCSI_IOCTL_GET_IDLUN ioctl was changed to include this
|
||
information. Hence this ioctl is only needed for
|
||
backward compatibility.
|
||
SCSI_IOCTL_TAGGED_ENABLE
|
||
Probably a remnant of the past when the mid level
|
||
addressed such issues. Now this functionality is
|
||
controlled by the lower level drivers. Best ignored.
|
||
SCSI_IOCTL_TAGGED_DISABLE
|
||
See comment for SCSI_IOCTL_TAGGED_ENABLE.
|
||
SCSI_IOCTL_PROBE_HOST
|
||
This ioctl expects its 3rd argument to be a pointer to
|
||
a union that looks like this:
|
||
union probe_host {
|
||
unsigned int length; /* [i] max length of
|
||
output ASCII string */
|
||
char str[length]; /* [o] N.B. may need '\0'
|
||
appended */
|
||
};
|
||
The host associated with the device's fd either has a
|
||
host dependent information string or failing that its
|
||
name, output into the given structure. Note that the
|
||
output starts at the beginning of given structure
|
||
(overwriting the input length). N.B. A trailing '\0'
|
||
may need to be put on the output string if it has been
|
||
truncated by the input length. A return value of 1
|
||
indicates the host is present, 0 indicates that the
|
||
host isn't present (how can that happen?) and a
|
||
negative value indicates an error.
|
||
|
||
SCSI_IOCTL_DOORLOCK
|
||
SCSI_IOCTL_DOORUNLOCK
|
||
SCSI_IOCTL_TEST_UNIT_READY
|
||
Returns 0 if the unit (device) is ready, a positive
|
||
number if it is not or a negative number when there
|
||
is an OS error.
|
||
|
||
SCSI_IOCTL_START_UNIT
|
||
SCSI_IOCTL_STOP_UNIT
|
||
SCSI_EMULATED_HOST {same as SG_EMULATED_HOST <new>}
|
||
|
||
SCSI_IOCTL_GET_PCI
|
||
Yields the PCI slot name (pci_dev::slot_name) associated with the lower
|
||
level (adapter) driver that controls the current device. Up to 8 characters
|
||
are output to the locations pointed to by 'arg'. If the current device
|
||
is not controlled by a PCI device then errno is set to ENXIO.
|
||
[This ioctl() was introduced in lk 2.4.4]
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.2. sd driver
|
||
|
||
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.2.1. sd compile options
|
||
|
||
|
||
MAX_RETRIES {5}
|
||
SD_TIMEOUT {30 seconds}
|
||
SD_MOD_TIMEOUT {75 seconds}
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.2.2. sd ioctls and user interface
|
||
|
||
The relevant files to see:
|
||
include/linux/hdreg.h
|
||
include/linux/genhd.h
|
||
include/linux/fs.h
|
||
|
||
A list of ioctl()s follow:
|
||
HDIO_GETGEO_BIG
|
||
HDIO_GETGEO [retrieve disk geometry]
|
||
BLKGETSIZE [number of sectors in device]
|
||
BLKROSET [set read only flag]
|
||
BLKROGET [get read only flag]
|
||
BLKRASET [set read ahead value]
|
||
BLKRAGET [get read ahead value]
|
||
BLKFLSBUF [instructs SCSI subsystem to flush buffers]
|
||
BLKSSZGET [get device block size]
|
||
BLKPG [partition table manipulation]
|
||
BLKELVGET [get elevator parameters]
|
||
BLKELVSET [set elevator parameters]
|
||
BLKRRPART [reread the partition table]
|
||
|
||
open() (all flags ignored)
|
||
close()
|
||
ioctl() (see list above)
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.3. sr driver
|
||
|
||
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.3.1. sr compile options
|
||
|
||
None.
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.3.2. sr ioctls and user interface
|
||
|
||
See the following files:
|
||
/usr/src/linux/include/linux/cdrom.h
|
||
/usr/src/linux/drivers/cdrom/cdrom.c [revision history section]
|
||
/usr/src/linux/Documentation/cdrom/cdrom-standard.tex
|
||
|
||
Some of the following ioctls are described in cdrom-standard.tex :
|
||
CDROMCLOSETRAY
|
||
CDROM_SET_OPTIONS
|
||
CDROM_CLEAR_OPTIONS
|
||
CDROM_SELECT_SPEED
|
||
CDROM_SELECT_DISC
|
||
CDROM_MEDIA_CHANGED
|
||
CDROM_DRIVE_STATUS
|
||
CDROM_CHANGER_NSLOTS
|
||
CDROM_LOCKDOOR
|
||
CDROM_DEBUG
|
||
CDROM_GET_CAPABILITY
|
||
DVD_READ_STRUCT
|
||
DVD_WRITE_STRUCT
|
||
DVD_AUTH
|
||
CDROM_SEND_PACKET
|
||
CDROM_NEXT_WRITABLE
|
||
CDROM_LAST_WRITTEN
|
||
|
||
The O_NONBLOCK flag on the open() of scd devices is important. Without it
|
||
the open() will wait until there is media in the device before returning.
|
||
open() O_NONBLOCK
|
||
close()
|
||
read()
|
||
write()
|
||
ioctl()
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.4. st driver
|
||
|
||
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.4.1. st compile options
|
||
|
||
Most of the following compile options can be overridden with boot/module
|
||
parameters and/or runtime configuration (i.e. ioctls).
|
||
|
||
The following parameters are defined in linux/drivers/scsi/st_options.h
|
||
ST_NOWAIT {0}
|
||
ST_IN_FILE_POS {0}
|
||
ST_RECOVERED_WRITE_FATAL {0}
|
||
ST_DEFAULT_BLOCK {0}
|
||
ST_BUFFER_BLOCKS {32}
|
||
ST_WRITE_THRESHOLD_BLOCKS {30}
|
||
ST_MAX_BUFFERS {4}
|
||
ST_MAX_SG {16}
|
||
ST_FIRST_SG {8}
|
||
ST_FIRST_ORDER {5}
|
||
ST_TWO_FM {0}
|
||
ST_BUFFER_WRITES {1}
|
||
ST_ASYNC_WRITES {1}
|
||
ST_READ_AHEAD {1}
|
||
ST_AUTO_LOCK {0}
|
||
ST_FAST_MTEOM {0}
|
||
ST_SCSI2LOGICAL {0}
|
||
ST_SYSV {0}
|
||
|
||
The following parameters are defined in linux/drivers/scsi/st.c
|
||
ST_TIMEOUT {900*HZ}
|
||
ST_LONG_TIMEOUT {14000*HZ}
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.4.2. st ioctls and user interface
|
||
|
||
The Linux tape interface is defined in /usr/src/linux/include/linux/mtio.h .
|
||
|
||
The following ioctl()s are listed in alphabetical order with a brief
|
||
explanation to the right. [See st documentation (especially man 4 st) for
|
||
more details.]
|
||
MTIOCTOP [execute tape commands and set drive/driver options]
|
||
MTIOCGET [get the status of the drive]
|
||
MTIOCPOS [get the current tape location]
|
||
|
||
open() O_RDONLY, O_RDWR
|
||
close()
|
||
read()
|
||
write()
|
||
ioctl()
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.5. sg driver
|
||
|
||
The following header files in the kernel source are relevant to the sg
|
||
driver:
|
||
/usr/src/linux/include/scsi/sg.h
|
||
|
||
As pointed out in Section E.1 this is best included in applications by
|
||
using:
|
||
#include <linux/../scsi/sg.h>
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.5.1. sg compile options
|
||
|
||
Here are some defines from the sg.h file that the user could conceivably
|
||
want to change. The current default values are shown in braces on the right:
|
||
SG_SCATTER_SZ {32768}
|
||
SG_DEF_RESERVED_SIZE {SG_SCATTER_SZ}
|
||
SG_DEF_FORCE_LOW_DMA {0}
|
||
SG_DEF_FORCE_PACK_ID {0}
|
||
SG_DEF_KEP_ORPHAN {0}
|
||
SG_MAX_QUEUE {16}
|
||
SG_DEFAULT_RETRIES {1} # i.e. don't retry
|
||
SG_BIG_BUFF {SG_DEF_RESERVED_SIZE}
|
||
SG_DEFAULT_TIMEOUT {60 seconds}
|
||
SG_DEF_COMMAND_Q {0 *}
|
||
SG_DEF_UNDERRUN_FLAG {0}
|
||
|
||
* The per file descriptor copy of this flips to 1 (thus
|
||
allowing command queuing) as soon as a write() based
|
||
on the newer sg_io_hdr structure is detected.
|
||
-----------------------------------------------------------------------------
|
||
|
||
E.5.2. sg ioctls and user interface
|
||
|
||
The following ioctl()s are listed in alphabetical order with a brief
|
||
explanation to the right. [See sg documentation for more details.]
|
||
SG_EMULATED_HOST [indicate if adapter is ide-scsi]
|
||
SG_GET_COMMAND_Q [command queuing flag state]
|
||
SG_GET_KEEP_ORPHAN [interrupted SG_IO keep orphan flag state]
|
||
SG_GET_LOW_DMA ["low dma flag" (<= 16 MB on i386) state]
|
||
SG_GET_NUM_WAITING [number of responses waiting to be read()]
|
||
SG_GET_PACK_ID [pack_id of next to read() response
|
||
(-1 if none)]
|
||
SG_GET_REQUEST_TABLE [yields array of requests being processed]
|
||
SG_GET_RESERVED_SIZE [current size of reserved buffer]
|
||
SG_GET_SCSI_ID [a little more info than the mid level's
|
||
SCSI_IOCTL_GET_IDLUN ioctl]
|
||
SG_GET_SG_TABLESIZE [max entries in host's scatter gather table]
|
||
SG_GET_TIMEOUT [yields timeout (unit: jiffies
|
||
(10ms on i386))]
|
||
SG_GET_TRANSFORM [state of ide-scsi's transform flag]
|
||
SG_IO [send given SCSI command and wait for
|
||
response]
|
||
SG_NEXT_CMD_LEN [change command length of next command]
|
||
SG_SCSI_RESET [send a SCSI bus, device or host reset]
|
||
SG_SET_COMMAND_Q [set command queuing state {old=0, new=1}]
|
||
SG_SET_DEBUG [set debug level {0}]
|
||
SG_SET_KEEP_ORPHAN [set SG_IO's keep orphan flag {0}]
|
||
SG_SET_FORCE_LOW_DMA [force DMA buffer low (<= 16 MB on i386)
|
||
{0}]
|
||
SG_SET_FORCE_PACK_ID [so read() can fetch by pack_id {0}]
|
||
SG_SET_RESERVED_SIZE [change default buffer size
|
||
{SG_DEF_RESERVED_SIZE}]
|
||
SG_SET_TIMEOUT [change current timeout {60 secs} ]
|
||
SG_SET_TRANSFORM [set ide-scsi's ATAPI transform flag {0}]
|
||
|
||
open() [recognized oflags: O_RDONLY, O_RDWR, O_EXCL,
|
||
O_NONBLOCK]
|
||
close()
|
||
read()
|
||
write()
|
||
ioctl()
|
||
poll() [used when in O_NONBLOCK mode]
|
||
fasync() [enables generation of SIGIO signal for read()]
|
||
-----------------------------------------------------------------------------
|
||
|
||
Appendix F. References, Credits and Corrections
|
||
|
||
WEB. The following references are found on the web. Please alert the author
|
||
if any of these links become stale.
|
||
|
||
[W1] SCSI (draft) standards, resources: www.t10.org
|
||
|
||
[W2] Eric Youngdale is the chief architect of the Linux SCSI subsystem:
|
||
www.andante.org/scsi.html
|
||
|
||
[W4] The author's scsi generic (sg) site is: www.torque.net/sg. The Linux
|
||
Documentation Project's site includes the www.tldp.org/HOWTO/
|
||
SCSI-Generic-HOWTO/ . A (possibly later) version of that document can be
|
||
found at www.torque.net/sg/p/sg_v3_ho . The sg_utils and sg3_utils packages,
|
||
as tarballs and as binary and source rpms can also be found on this page.
|
||
These packages and others available for the sg driver are discussed at
|
||
www.torque.net/sg/u_index.html.
|
||
|
||
[W5] Richard Gooch's devfs site: www.atnf.csiro.au/~rgooch/linux/docs/
|
||
devfs.html
|
||
|
||
[W6] Kurt Garloff's site (including the scsidev and the scsiinfo
|
||
utilities): www.garloff.de/kurt/linux/. Kurt also has the damaged media
|
||
rescue program dd_rescue at this site: www.garloff.de/kurt/linux/ddrescue
|
||
|
||
[W7] Drew Eckhardt's SCSI-HOWTO from 1996 (in ASCII): metalab.unc.edu/pub/
|
||
Linux/docs/HOWTO/unmaintained/SCSI-HOWTO
|
||
|
||
[W8] Linux Documentation Project (LDP): tldp.org
|
||
|
||
[W9] SCSI Trade Association site has a lot of useful information:
|
||
www.scsita.org
|
||
|
||
[W10] SCSI FAQ site - useful source of information and links:
|
||
www.scsifaq.org
|
||
|
||
NEWSGROUPS. The following entries are actually reflectors rather than
|
||
newsgroups. Various web locations archive their contents (e.g.
|
||
marc.theaimsgroup.com).
|
||
|
||
[N1] Linux SCSI reflector: < linux-scsi@vger.kernel.org >. This is a
|
||
relatively low volume (circa 200 postings per month) Linux SCSI specific
|
||
group that many of the SCSI subsystem maintainers monitor.
|
||
|
||
[N2] Linux kernel reflector: < linux-kernel@vger.kernel.org >. This is a
|
||
relatively high volume (circa 5000 postings per month) group for all aspects
|
||
of the Linux kernel. The Linux SCSI reflector should be tried first.
|
||
|
||
BOOKS. Here are some books that the author found useful.
|
||
|
||
[B1] "Linux Device Drivers" Second edition by Alessandro Rubini and
|
||
Jonathan Corbet [O'Reilly 2001 ISBN 0-596-00008-1] This is a solid text on
|
||
Linux device drivers including some information on the SCSI subsystem. It
|
||
covers the block subsystem well and has many char device driver examples. It
|
||
has been updated for the Linux 2.4 series kernels and also includes
|
||
information on the Linux 2.2 and 2.0 series. This book is highly recommended.
|
||
The authors and the publisher have unselfishly made this book available under
|
||
the GNU Free Documentation License (version 1.1). It can be found in html at
|
||
www.xml.com/ldd/chapter/book .
|
||
|
||
[B2] "Running Linux" 3rd edition by M. Welsh, M. K. Dalheimer & L. Kaufman
|
||
[O'Reilly 1999 ISBN 1-56592-469-X] This is a classic Linux tome which
|
||
includes some SCSI configuration info.
|
||
|
||
[B3] "The Programmer's Guide to SCSI" by Brian Sawert [Addison Wesley 1998
|
||
ISBN 0-201-18538-5] This book covers many SCSI topics, including the pass
|
||
through mechanisms of Linux (sg) and ASPI/ASPI32 as used by Windows.
|
||
|
||
CREDITS. The author is grateful for the following contributions:
|
||
|
||
<EFBFBD><EFBFBD>*<2A>Kai M<>kisara (st) <Kai.Makisara at metla dot fi>
|
||
|
||
<EFBFBD><EFBFBD>*<2A>Jens Axboe (sr) <axboe at suse dot de>
|
||
|
||
<EFBFBD><EFBFBD>*<2A>Richard Gooch (devfs) <rgooch at atnf dot csiro dot au>
|
||
|
||
<EFBFBD><EFBFBD>*<2A>Tim Waugh (ppa, imm, ppscsi + docbook) <twaugh at redhat dot com>
|
||
|
||
<EFBFBD><EFBFBD>*<2A>Gadi Oxman (ide-scsi) <gadio at netvision dot net dot il>
|
||
|
||
|
||
CORRECTIONS and SUGGESTIONS. Please send any corrections or suggestions to
|
||
the author at <dgilbert at interlog dot com> or <dougg at torque dot net> .
|
||
|
||
Notes
|
||
|
||
[1] SCSI standards allow for multiple initiators to be present on a single
|
||
bus. This is not well supported in Linux although there are patches
|
||
around that improve this situation.
|
||
[2] If 15 partitions is too limiting then the Logical Volume Manager (LVM)
|
||
might be considered. See /usr/src/linux/Documentation/LVM-HOWTO . LVM
|
||
will also allow a logical partition to span multiple block devices.
|
||
[3] One slight wrinkle with grub is that /etc/grub.conf is a symbolic link
|
||
to /boot/grub/grub.conf. This can be useful to know when /boot is a
|
||
separate partition.
|
||
[4] There is a sequencing issue here if the root file system is on the SCSI
|
||
device controlled by the lower level (adapter) driver to be loaded since
|
||
it contains the /etc/modules.conf file. Also there is the issue of how
|
||
the boot loader obtains the initial kernel image from a SCSI device
|
||
(often from the (master) boot record). The latter is usually taken care
|
||
of by the system's or adapter card's BIOS.
|
||
[5] An example of using mkinitrd: assume the root partition is on a SCSI
|
||
disk connected to a controller from Adaptec that requires the aic7xxx
|
||
driver. After building a kernel with the aic7xxx driver specified as a
|
||
module then load the image into the normal place (probably in the /boot
|
||
directory). Next make sure a line like "alias scsi_hostadapter aic7xxx"
|
||
is in the /etc/modules.conf file. Then from the /boot directory execute
|
||
a line like mkinitrd /boot/initrd-2.4.5.img 2.4.5 (this assumes lk 2.4.5
|
||
is being build). This should result in the file initrd-2.4.5.img being
|
||
created. The /etc/lilo.conf should then have a section added looking
|
||
something like this:
|
||
image=/boot/vmlinuz-2.4.5
|
||
label=linux
|
||
initrd=/boot/initrd-2.4.5.img
|
||
read-only
|
||
root=/dev/sda7
|
||
The following should also be selected in the kernel configuration:
|
||
CONFIG_BLK_DEV_RAM=y
|
||
CONFIG_BLK_DEV_RAM_SIZE=4096
|
||
CONFIG_BLK_DEV_INITRD=y
|
||
See also Documentation/initrd.txt.
|
||
[6] PCI adapters are much "safer" for initialization code than the older ISA
|
||
adapters. Hence the order of initialization of PCI adapters is unlikely
|
||
to lead to lockups. In this case the order of initialization (and thus
|
||
SCSI adapter numbers) of built in drivers may be modified by changing
|
||
the order of entries in the SCSI subsystem Makefile ( /usr/src/linux/
|
||
drivers/scsi/Makefile). Beware: some adapters may be recognized by more
|
||
than one lower level driver (e.g. those based on NCR chipsets).
|
||
[7] Either comma or colon can be delimiters for "scsihosts". This means that
|
||
"scsihosts=advansys,imm,,ide-scsi" is also valid. Also if a machine's
|
||
boot sequence involves an "initrd" stage (look in /etc/grub.conf or /etc
|
||
/lilo.conf to find out if this is the case), then the mkinitrd command
|
||
should be run after a change to the "scsihosts" boot time parameter.
|
||
This will generate a new initrd image that needs to be put in the
|
||
correct place (most probably in the /boot directory).
|
||
[8] Using "scsihosts" can lead to a situation in which the computer's BIOS
|
||
finds the boot track (and hence boot time parameters set in lilo or
|
||
grub) on one disk while the kernel finds the root partition on another
|
||
disk. This can be quite confusing when it is unplanned. Hence after
|
||
changing (or adding) "scsihosts" in lilo or grub's configuration, it may
|
||
be wise to boot the machine to see which disks are accessed.
|
||
[9] The parsing of "add-single-device" and "remove-single-device" is rather
|
||
inflexible. Hence it is best to stay close to the demonstrated syntax
|
||
with no extra spaces (and no tabs).
|
||
[10] ATA is the modern name for what was previously known as IDE and/or EIDE.
|
||
Note that the subsystem that controls ATA devices in Linux is called the
|
||
"IDE" subsystem for historical reasons.
|
||
[11] Other ATA devices such as tapes and floppies often use the ATAPI
|
||
interface. However, the vast majority of ATA disks do not use the ATAPI
|
||
interface.
|
||
[12] In the linux 2.4 kernel series there has been an increase in problems
|
||
when the ide-scsi driver is used so that cdrecord can control ATAPI
|
||
(IDE) cd writers. The problem may be related to the aggressive manner in
|
||
which the IDE subsystem attempts to optimize the speed of data transfers
|
||
on devices it controls. Some people experiencing timeouts and machine
|
||
lockups have found that reducing the DMA setting via the hdparm command
|
||
has fixed the problem. If the cd writer is connected to /dev/hdd then
|
||
users have reported success with one of these two commands:
|
||
hdparm -d0 -c1 /dev/hdd
|
||
hdparm -d 1 -X 34 /dev/hdd
|
||
The first one turns off DMA completely while the second one sets it in
|
||
"multiword DMA mode 2". Cd writers do not need the types of speeds that
|
||
modern disks utilize. Even burning at "x16" implies a sustained transfer
|
||
rate of 16 times 150 KB/sec which is approximately 2.4 MB/sec, not
|
||
really that fast. There has also been a report that moving a cd writer
|
||
off a high speed IDE controller (Promise) and back to the motherboard's
|
||
lower speed IDE controllers has fixed a random IDE bus reset problem.
|
||
Another report suggests reducing (or turning off) the DMA on the IDE
|
||
hard disk can also stop lockups.
|
||
[13] It has been reported that in some distributions the attempt to use the
|
||
hdparm command fails. In this case use the "echo ... > /proc/ide/hdx/
|
||
settings" form.
|
||
[14] This list has been compiled from the official 2.4 series kernels
|
||
released at [http://www.kernel.org] www.kernel.org. Distributions are
|
||
free to tailor the official kernels and this may impact what is
|
||
supported (or changed) in the SCSI subsystem. For example this machine
|
||
reports this kernel: "2.4.18-27.8.0". So that is roughly based on the
|
||
official 2.4.18 kernel which the vendor has "modded" 27 times for the
|
||
"8.0" level of their distribution. As an example of the type of changes,
|
||
the aic7xxx driver in the official 2.4.18 does not support Adaptec's
|
||
Ultra 320 series of PCI adapters; however that vendor's version does.
|