200 lines
3.9 KiB
HTML
200 lines
3.9 KiB
HTML
<HTML
|
|
><HEAD
|
|
><TITLE
|
|
>dxfer_direction</TITLE
|
|
><META
|
|
NAME="GENERATOR"
|
|
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
|
|
"><LINK
|
|
REL="HOME"
|
|
TITLE="The Linux SCSI Generic (sg) HOWTO"
|
|
HREF="index.html"><LINK
|
|
REL="UP"
|
|
TITLE="The sg_io_hdr_t structure in detail"
|
|
HREF="sg_io_hdr_t.html"><LINK
|
|
REL="PREVIOUS"
|
|
TITLE="interface_id"
|
|
HREF="x163.html"><LINK
|
|
REL="NEXT"
|
|
TITLE="cmd_len"
|
|
HREF="x184.html"></HEAD
|
|
><BODY
|
|
CLASS="SECT1"
|
|
BGCOLOR="#FFFFFF"
|
|
TEXT="#000000"
|
|
LINK="#0000FF"
|
|
VLINK="#840084"
|
|
ALINK="#0000FF"
|
|
><DIV
|
|
CLASS="NAVHEADER"
|
|
><TABLE
|
|
SUMMARY="Header navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TH
|
|
COLSPAN="3"
|
|
ALIGN="center"
|
|
>The Linux SCSI Generic (sg) HOWTO</TH
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="left"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="x163.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="80%"
|
|
ALIGN="center"
|
|
VALIGN="bottom"
|
|
>Chapter 6. The sg_io_hdr_t structure in detail</TD
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="right"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="x184.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"></DIV
|
|
><DIV
|
|
CLASS="SECT1"
|
|
><H1
|
|
CLASS="SECT1"
|
|
><A
|
|
NAME="AEN166">6.2. dxfer_direction</H1
|
|
><P
|
|
>The type of dxfer_direction is int.
|
|
This is required to be one of the following:
|
|
<P
|
|
></P
|
|
><UL
|
|
><LI
|
|
><P
|
|
>SG_DXFER_NONE /* e.g. a SCSI Test Unit Ready command */</P
|
|
></LI
|
|
><LI
|
|
><P
|
|
>SG_DXFER_TO_DEV /* e.g. a SCSI WRITE command */</P
|
|
></LI
|
|
><LI
|
|
><P
|
|
>SG_DXFER_FROM_DEV /* e.g. a SCSI READ command */</P
|
|
></LI
|
|
><LI
|
|
><P
|
|
>SG_DXFER_TO_FROM_DEV</P
|
|
></LI
|
|
><LI
|
|
><P
|
|
>SG_DXFER_UNKNOWN</P
|
|
></LI
|
|
></UL
|
|
>
|
|
The value SG_DXFER_NONE should be used when there is no data transfer
|
|
associated with a command (e.g. TEST UNIT READY). The value
|
|
SG_DXFER_TO_DEV should be used when data is being moved from user
|
|
memory towards the device (e.g. WRITE). The value SG_DXFER_FROM_DEV
|
|
should be used when data is being moved from the device towards user
|
|
memory (e.g. READ).</P
|
|
><P
|
|
> The value SG_DXFER_TO_FROM_DEV is only relevant to indirect IO
|
|
(otherwise it is treated like SG_DXFER_FROM_DEV). Data is moved from
|
|
the user space to the kernel buffers. The command is then performed and
|
|
most likely a READ-like command transfers data from the device into the
|
|
kernel buffers. Finally the kernel buffers are copied back into the user
|
|
space. This technique allows application writers to initialize the
|
|
buffer and perhaps deduce the number of bytes actually read from the
|
|
device (i.e. detect underrun). This is better done by using 'resid' if
|
|
it is supported.</P
|
|
><P
|
|
> The value SG_DXFER_UNKNOWN is for those (rare) situations where the
|
|
data direction is not known. It may be useful for backward
|
|
compatibility of existing applications when the relevant direction
|
|
information is not available in the sg interface layer. There is
|
|
a (minor) performance "hit" associated with choosing this
|
|
option (e.g. on the PCI bus). Some recent pseudo device drivers (e.g.
|
|
USB mass storage) may have problems handling this value (especially
|
|
on vendor-specific SCSI commands).</P
|
|
><P
|
|
> N.B. 'dxfer_direction' must have one of the five indicated values
|
|
and cannot be uninitialized or zero.</P
|
|
><P
|
|
> If 'dxfer_len' is zero then all values are treated like SG_DXFER_NONE.</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="NAVFOOTER"
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"><TABLE
|
|
SUMMARY="Footer navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="x163.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="index.html"
|
|
ACCESSKEY="H"
|
|
>Home</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="x184.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
>interface_id</TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="sg_io_hdr_t.html"
|
|
ACCESSKEY="U"
|
|
>Up</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
>cmd_len</TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></BODY
|
|
></HTML
|
|
> |