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| author | Kay Sievers <kay.sievers@vrfy.org> | 2011-07-31 22:08:04 +0200 |
|---|---|---|
| committer | Jens Axboe <jaxboe@fusionio.com> | 2011-07-31 22:08:04 +0200 |
| commit | 770fe30a46a12b6fb6b63fbe1737654d28e84844 (patch) | |
| tree | e8a35712602ca086c41f94d191579ac2dc365cf5 /include/linux/loop.h | |
| parent | 34dd82afd27da2537199d7f71f1542501c6f96e7 (diff) | |
| download | linux-770fe30a46a12b6fb6b63fbe1737654d28e84844.tar.gz linux-770fe30a46a12b6fb6b63fbe1737654d28e84844.tar.bz2 linux-770fe30a46a12b6fb6b63fbe1737654d28e84844.zip | |
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>
Diffstat (limited to 'include/linux/loop.h')
| -rw-r--r-- | include/linux/loop.h | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/include/linux/loop.h b/include/linux/loop.h index 5f08d18fa148..683d69890119 100644 --- a/include/linux/loop.h +++ b/include/linux/loop.h @@ -160,4 +160,8 @@ int loop_unregister_transfer(int number); #define LOOP_CHANGE_FD 0x4C06 #define LOOP_SET_CAPACITY 0x4C07 +/* /dev/loop-control interface */ +#define LOOP_CTL_ADD 0x4C80 +#define LOOP_CTL_REMOVE 0x4C81 +#define LOOP_CTL_GET_FREE 0x4C82 #endif |