[PATCH 2/2] loop: handle on-demand devices correctly

Namhyung Kim
2011-05-24T14:36:16Z

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>
---
drivers/block/loop.c | 8 ++++----
1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index cbf7052d1dd5..c59a672a3de0 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -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);
--
1.7.5.2