Commit a1c15c59 authored May 24, 2011 by Namhyung Kim Committed by Jens Axboe May 24, 2011

loop: handle on-demand devices correctly



When finding or allocating a loop device, loop_probe() did not take
partition numbers into account so that it can result to a different
device. Consider following example:

$ sudo modprobe loop max_part=15
$ ls -l /dev/loop*
brw-rw---- 1 root disk 7,   0 2011-05-24 22:16 /dev/loop0
brw-rw---- 1 root disk 7,  16 2011-05-24 22:16 /dev/loop1
brw-rw---- 1 root disk 7,  32 2011-05-24 22:16 /dev/loop2
brw-rw---- 1 root disk 7,  48 2011-05-24 22:16 /dev/loop3
brw-rw---- 1 root disk 7,  64 2011-05-24 22:16 /dev/loop4
brw-rw---- 1 root disk 7,  80 2011-05-24 22:16 /dev/loop5
brw-rw---- 1 root disk 7,  96 2011-05-24 22:16 /dev/loop6
brw-rw---- 1 root disk 7, 112 2011-05-24 22:16 /dev/loop7
$ sudo mknod /dev/loop8 b 7 128
$ sudo losetup /dev/loop8 ~/temp/disk-with-3-parts.img
$ sudo losetup -a
/dev/loop128: [0805]:278201 (/home/namhyung/temp/disk-with-3-parts.img)
$ ls -l /dev/loop*
brw-rw---- 1 root disk 7,    0 2011-05-24 22:16 /dev/loop0
brw-rw---- 1 root disk 7,   16 2011-05-24 22:16 /dev/loop1
brw-rw---- 1 root disk 7, 2048 2011-05-24 22:18 /dev/loop128
brw-rw---- 1 root disk 7, 2049 2011-05-24 22:18 /dev/loop128p1
brw-rw---- 1 root disk 7, 2050 2011-05-24 22:18 /dev/loop128p2
brw-rw---- 1 root disk 7, 2051 2011-05-24 22:18 /dev/loop128p3
brw-rw---- 1 root disk 7,   32 2011-05-24 22:16 /dev/loop2
brw-rw---- 1 root disk 7,   48 2011-05-24 22:16 /dev/loop3
brw-rw---- 1 root disk 7,   64 2011-05-24 22:16 /dev/loop4
brw-rw---- 1 root disk 7,   80 2011-05-24 22:16 /dev/loop5
brw-rw---- 1 root disk 7,   96 2011-05-24 22:16 /dev/loop6
brw-rw---- 1 root disk 7,  112 2011-05-24 22:16 /dev/loop7
brw-r--r-- 1 root root 7,  128 2011-05-24 22:17 /dev/loop8

After this patch, /dev/loop8 - instead of /dev/loop128 - was
accessed correctly.

In addition, 'range' passed to blk_register_region() should
include all range of dev_t that LOOP_MAJOR can address. It does
not need to be limited by partition numbers unless 'max_loop'
param was specified.

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Laurent Vivier <Laurent.Vivier@bull.net>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

parent 78f4bb36

drivers/block/loop.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -1658,7 +1658,7 @@ static struct kobject loop_probe(dev_t dev, int part, void *data)
		struct kobject *kobj;

		mutex_lock(&loop_devices_mutex);
		lo = loop_init_one(dev & MINORMASK);
		lo = loop_init_one(MINOR(dev) >> part_shift);
		kobj = lo ? get_disk(lo->lo_disk) : ERR_PTR(-ENOMEM);
		mutex_unlock(&loop_devices_mutex);

		@@ -1699,10 +1699,10 @@ static int __init loop_init(void)

		if (max_loop) {
		nr = max_loop;
		range = max_loop;
		range = max_loop << part_shift;
		} else {
		nr = 8;
		range = 1UL << (MINORBITS - part_shift);
		range = 1UL << MINORBITS;
		}

		if (register_blkdev(LOOP_MAJOR, "loop"))
		@@ -1741,7 +1741,7 @@ static void __exit loop_exit(void)
		unsigned long range;
		struct loop_device lo, next;

		range = max_loop ? max_loop : 1UL << (MINORBITS - part_shift);
		range = max_loop ? max_loop << part_shift : 1UL << MINORBITS;

		list_for_each_entry_safe(lo, next, &loop_devices, lo_list)
		loop_del_one(lo);

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