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authorKay Sievers <kay.sievers@vrfy.org>2011-07-31 22:08:04 +0200
committerJens Axboe <jaxboe@fusionio.com>2011-07-31 22:08:04 +0200
commit770fe30a46a12b6fb6b63fbe1737654d28e84844 (patch)
treee8a35712602ca086c41f94d191579ac2dc365cf5 /include/linux/loop.h
parent34dd82afd27da2537199d7f71f1542501c6f96e7 (diff)
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.h4
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