mirror of https://github.com/mkerrisk/man-pages
loop.4: New page documenting the loop device
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Urs Thuermann
Michael Kerrisk
parent
57713dcad5
commit
42404315aa
|
|
@ -0,0 +1,140 @@
|
|||
.\" loop.4
|
||||
.\" Copyright 2002 Urs Thuermann (urs@isnogud.escape.de)
|
||||
.\"
|
||||
.\" This is free documentation; you can redistribute it and/or
|
||||
.\" modify it under the terms of the GNU General Public License as
|
||||
.\" published by the Free Software Foundation; either version 2 of
|
||||
.\" the License, or (at your option) any later version.
|
||||
.\"
|
||||
.\" The GNU General Public License's references to "object code"
|
||||
.\" and "executables" are to be interpreted as the output of any
|
||||
.\" document formatting or typesetting system, including
|
||||
.\" intermediate and printed output.
|
||||
.\"
|
||||
.\" This manual is distributed in the hope that it will be useful,
|
||||
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||||
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||||
.\" GNU General Public License for more details.
|
||||
.\"
|
||||
.\" You should have received a copy of the GNU General Public
|
||||
.\" License along with this manual; if not, write to the Free
|
||||
.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
|
||||
.\" USA.
|
||||
.\"
|
||||
.\" $Id: loop.4,v 1.2 2005/12/05 19:03:01 urs Exp urs $
|
||||
.\"
|
||||
.TH LOOP 4 "2005-12-05" "Linux" "Linux Programmer's Manual"
|
||||
.SH NAME
|
||||
loop \- Driver for loop devices
|
||||
.SH SYNOPSIS
|
||||
#include <linux/loop.h>
|
||||
...
|
||||
.SH DESCRIPTION
|
||||
The loop device is a block device that maps its data blocks not to a
|
||||
physical device like a hard disk or CDROM drive, but to the blocks of
|
||||
a regular file in a file system or to another block device. This can
|
||||
be useful for example to provide a block device for a file system
|
||||
image stored in a file, so that it can be mounted with the
|
||||
.BR mount (8)
|
||||
command. You could do
|
||||
.nf
|
||||
.IP
|
||||
# dd if=/dev/fd0 of=floppy.img
|
||||
# losetup /dev/loop0 floppy/img
|
||||
# mount /dev/loop0 /mnt
|
||||
.fi
|
||||
.LP
|
||||
See
|
||||
.BR losetup (8)
|
||||
for another example.
|
||||
|
||||
A transfer function can be specified for each loop device for
|
||||
encryption and decryption purposes.
|
||||
|
||||
The following ioctl's are provided by the loop block device:
|
||||
.TP
|
||||
.B LOOP_SET_FD
|
||||
Associate the loop device with the open file whose file descriptor is
|
||||
passed as the ioctl command argument.
|
||||
.TP
|
||||
.B LOOP_CLR_FD
|
||||
Disassociate the loop device from any file descriptor.
|
||||
.TP
|
||||
.B LOOP_SET_STATUS
|
||||
Set the status of the loop device as defined by the struct loop_info
|
||||
passed as command argument. The loop_info structure is defined in
|
||||
<linux/loop.h> as
|
||||
.PP
|
||||
.RS
|
||||
.nf
|
||||
.ft B
|
||||
struct loop_info {
|
||||
int lo_number; /* ioctl r/o */
|
||||
dev_t lo_device; /* ioctl r/o */
|
||||
unsigned long lo_inode; /* ioctl r/o */
|
||||
dev_t lo_rdevice; /* ioctl r/o */
|
||||
int lo_offset;
|
||||
int lo_encrypt_type;
|
||||
int lo_encrypt_key_size; /* ioctl w/o */
|
||||
int lo_flags; /* ioctl r/o */
|
||||
char lo_name[LO_NAME_SIZE];
|
||||
unsigned char lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */
|
||||
unsigned long lo_init[2];
|
||||
char reserved[4];
|
||||
};
|
||||
.ft R
|
||||
.fi
|
||||
|
||||
The encryption type should be one of
|
||||
.BR LO_CRYPT_NONE ,
|
||||
.BR LO_CRYPT_XOR ,
|
||||
.BR LO_CRYPT_DES ,
|
||||
.BR LO_CRYPT_FISH2 ,
|
||||
.BR LO_CRYPT_BLOW ,
|
||||
.BR LO_CRYPT_CAST128 ,
|
||||
.BR LO_CRYPT_IDEA ,
|
||||
.BR LO_CRYPT_DUMMY ,
|
||||
.BR LO_CRYPT_SKIPJACK .
|
||||
.RE
|
||||
.TP
|
||||
.B LOOP_GET_STATUS
|
||||
Get the status of the loop device. The ioctl command argument must be
|
||||
a pointer to a struct loop_info.
|
||||
.PP
|
||||
Since Linux kernel 2.6 there are two new ioctl's:
|
||||
.TP
|
||||
.BR LOOP_SET_STATUS64 ", " LOOP_GET_STATUS64
|
||||
These are similar to
|
||||
.BR LOOP_SET_STATUS " and " LOOP_GET_STATUS
|
||||
described above but use the loop_info64 structure, that has some
|
||||
additional fields and a larger range for some other fields:
|
||||
.PP
|
||||
.RS
|
||||
.nf
|
||||
.ft B
|
||||
struct loop_info64 {
|
||||
__u64 lo_device; /* ioctl r/o */
|
||||
__u64 lo_inode; /* ioctl r/o */
|
||||
__u64 lo_rdevice; /* ioctl r/o */
|
||||
__u64 lo_offset;
|
||||
__u64 lo_sizelimit;/* bytes, 0 == max available */
|
||||
__u32 lo_number; /* ioctl r/o */
|
||||
__u32 lo_encrypt_type;
|
||||
__u32 lo_encrypt_key_size; /* ioctl w/o */
|
||||
__u32 lo_flags; /* ioctl r/o */
|
||||
__u8 lo_file_name[LO_NAME_SIZE];
|
||||
__u8 lo_crypt_name[LO_NAME_SIZE];
|
||||
__u8 lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */
|
||||
__u64 lo_init[2];
|
||||
};
|
||||
.fi
|
||||
.RE
|
||||
|
||||
.SH FILES
|
||||
/dev/loop[0-7]: The loop block special device files
|
||||
|
||||
.SH "SEE ALSO"
|
||||
.BR losetup (8),
|
||||
.BR mount (8)
|
||||
|
||||
|
||||
Loading…
Reference in New Issue