linux/drivers/block
Kay Sievers 770fe30a46 loop: add management interface for on-demand device allocation
Loop devices today have a fixed pre-allocated number of usually 8.
The number can only be changed at module init time. To find a free
device to use, /dev/loop%i needs to be scanned, and all devices need
to be opened until a free one is possibly found.

This adds a new /dev/loop-control device node, that allows to
dynamically find or allocate a free device, and to add and remove loop
devices from the running system:
 LOOP_CTL_ADD adds a specific device. Arg is the number
 of the device. It returns the device i or a negative
 error code.

 LOOP_CTL_REMOVE removes a specific device, Arg is the
 number the device. It returns the device i or a negative
 error code.

 LOOP_CTL_GET_FREE finds the next unbound device or allocates
 a new one. No arg is given. It returns the device i or a
 negative error code.

The loop kernel module gets automatically loaded when
/dev/loop-control is accessed the first time. The alias
specified in the module, instructs udev to create this
'dead' device node, even when the module is not loaded.

Example:
 cfd = open("/dev/loop-control", O_RDWR);

 # add a new specific loop device
 err = ioctl(cfd, LOOP_CTL_ADD, devnr);

 # remove a specific loop device
 err = ioctl(cfd, LOOP_CTL_REMOVE, devnr);

 # find or allocate a free loop device to use
 devnr = ioctl(cfd, LOOP_CTL_GET_FREE);

 sprintf(loopname, "/dev/loop%i", devnr);
 ffd = open("backing-file", O_RDWR);
 lfd = open(loopname, O_RDWR);
 err = ioctl(lfd, LOOP_SET_FD, ffd);

Cc: Tejun Heo <tj@kernel.org>
Cc: Karel Zak  <kzak@redhat.com>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2011-07-31 22:08:04 +02:00
..
aoe drivers/block/aoe/Makefile: replace the use of <module>-objs with <module>-y 2011-01-19 08:25:02 -07:00
drbd Merge branch 'for-3.0-important' of git://git.drbd.org/linux-2.6-drbd into for-linus 2011-06-30 10:10:50 +02:00
paride block: fix mismerge of the DISK_EVENT_MEDIA_CHANGE removal 2011-06-02 05:29:19 +09:00
xen-blkback Merge branch 'for-3.1/drivers' of git://git.kernel.dk/linux-block 2011-07-25 10:38:18 -07:00
amiflop.c block: unexport DISK_EVENT_MEDIA_CHANGE for legacy/fringe drivers 2011-04-21 21:33:05 +02:00
ataflop.c block: unexport DISK_EVENT_MEDIA_CHANGE for legacy/fringe drivers 2011-04-21 21:33:05 +02:00
brd.c brd: export module parameters 2011-05-26 21:06:50 +02:00
cciss_cmd.h cciss: use new doorbell-bit-5 reset method 2011-05-06 08:23:55 -06:00
cciss_scsi.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
cciss_scsi.h cciss: add cciss_tape_cmds module paramter 2011-05-06 08:23:59 -06:00
cciss.c cciss: fix compile issue 2011-05-06 08:27:00 -06:00
cciss.h cciss: do not attempt to read from a write-only register 2011-07-09 09:04:12 +02:00
cpqarray.c block: remove per-queue plugging 2011-03-10 08:52:07 +01:00
cpqarray.h
cryptoloop.c
DAC960.c block: unexport DISK_EVENT_MEDIA_CHANGE for legacy/fringe drivers 2011-04-21 21:33:05 +02:00
DAC960.h
floppy.c Merge branch 'idle-release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-idle-2.6 2011-05-29 11:18:09 -07:00
hd.c i8253: Create linux/i8253.h and use it in all 8253 related files 2011-06-09 15:01:37 +02:00
ida_cmd.h
ida_ioctl.h
Kconfig xen/blkback: Flesh out the description in the Kconfig. 2011-05-12 17:55:40 -04:00
loop.c loop: add management interface for on-demand device allocation 2011-07-31 22:08:04 +02:00
Makefile xen/blkback: Move it from drivers/xen to drivers/block 2011-04-18 14:30:26 -04:00
mg_disk.c block: switch s390 tape_block and mg_disk to elevator_change() 2010-08-23 14:02:44 +02:00
nbd.c nbd: adjust 'max_part' according to part_shift 2011-05-28 14:44:46 +02:00
osdblk.c block: remove spurious uses of REQ_HARDBARRIER 2010-09-10 12:35:36 +02:00
pktcdvd.c kill useless checks for sb->s_op == NULL 2011-07-20 01:44:21 -04:00
ps3disk.c Merge branch 'for-2.6.37/barrier' of git://git.kernel.dk/linux-2.6-block 2010-10-22 17:07:18 -07:00
ps3vram.c
rbd_types.h rbd: introduce rados block device (rbd), based on libceph 2010-10-20 15:38:13 -07:00
rbd.c rbd: set blk_queue request sizes to object size 2011-07-26 11:29:35 -07:00
smart1,2.h fix typos 'comamnd' -> 'command' in comments 2011-02-02 11:31:21 +01:00
sunvdc.c
swim3.c block: unexport DISK_EVENT_MEDIA_CHANGE for legacy/fringe drivers 2011-04-21 21:33:05 +02:00
swim_asm.S
swim.c block: unexport DISK_EVENT_MEDIA_CHANGE for legacy/fringe drivers 2011-04-21 21:33:05 +02:00
sx8.c
ub.c block: unexport DISK_EVENT_MEDIA_CHANGE for legacy/fringe drivers 2011-04-21 21:33:05 +02:00
umem.c Merge branch 'for-2.6.39/stack-plug' into for-2.6.39/core 2011-03-10 08:58:35 +01:00
umem.h
viodasd.c Fix common misspellings 2011-03-31 11:26:23 -03:00
virtio_blk.c drivers, block: virtio_blk: Replace cryptic number with the macro 2011-05-30 11:14:13 +09:30
xd.c block: autoconvert trivial BKL users to private mutex 2010-10-05 15:01:10 +02:00
xd.h
xen-blkfront.c xen-blkfront: Introduce BLKIF_OP_FLUSH_DISKCACHE support. 2011-05-12 08:56:03 -04:00
xsysace.c dt: remove extra xsysace platform_driver registration 2011-07-14 05:33:52 -06:00
z2ram.c drivers/block/z2ram.c: correct printing of sector_t 2010-10-28 06:15:26 -06:00