[136/146] brd: handle on-demand devices correctly

Greg KH
2011-06-01T08:18:40Z

From: Namhyung Kim <namhyung@gmail.com>

commit af46566885a373b0a526932484cd8fef8de7b598 upstream.

When finding or allocating a ram disk device, brd_probe() did not take
partition numbers into account so that it can result to a different
device. Consider following example (I set CONFIG_BLK_DEV_RAM_COUNT=4
for simplicity) :

$ sudo modprobe brd max_part=15
$ ls -l /dev/ram*
brw-rw---- 1 root disk 1, 0 2011-05-25 15:41 /dev/ram0
brw-rw---- 1 root disk 1, 16 2011-05-25 15:41 /dev/ram1
brw-rw---- 1 root disk 1, 32 2011-05-25 15:41 /dev/ram2
brw-rw---- 1 root disk 1, 48 2011-05-25 15:41 /dev/ram3
$ sudo mknod /dev/ram4 b 1 64
$ sudo dd if=/dev/zero of=/dev/ram4 bs=4k count=256
256+0 records in
256+0 records out
1048576 bytes (1.0 MB) copied, 0.00215578 s, 486 MB/s
namhyung@leonhard:linux$ ls -l /dev/ram*
brw-rw---- 1 root disk 1, 0 2011-05-25 15:41 /dev/ram0
brw-rw---- 1 root disk 1, 16 2011-05-25 15:41 /dev/ram1
brw-rw---- 1 root disk 1, 32 2011-05-25 15:41 /dev/ram2
brw-rw---- 1 root disk 1, 48 2011-05-25 15:41 /dev/ram3
brw-r--r-- 1 root root 1, 64 2011-05-25 15:45 /dev/ram4
brw-rw---- 1 root disk 1, 1024 2011-05-25 15:44 /dev/ram64

After this patch, /dev/ram4 - instead of /dev/ram64 - was
accessed correctly.

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

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/block/brd.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -552,7 +552,7 @@ static struct kobject *brd_probe(dev_t d
struct kobject *kobj;

mutex_lock(&brd_devices_mutex);
- brd = brd_init_one(dev & MINORMASK);
+ brd = brd_init_one(MINOR(dev) >> part_shift);
kobj = brd ? get_disk(brd->brd_disk) : ERR_PTR(-ENOMEM);
mutex_unlock(&brd_devices_mutex);

@@ -593,10 +593,10 @@ static int __init brd_init(void)

if (rd_nr) {
nr = rd_nr;
- range = rd_nr;
+ range = rd_nr << part_shift;
} else {
nr = CONFIG_BLK_DEV_RAM_COUNT;
- range = 1UL << (MINORBITS - part_shift);
+ range = 1UL << MINORBITS;
}

if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
@@ -635,7 +635,7 @@ static void __exit brd_exit(void)
unsigned long range;
struct brd_device *brd, *next;

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

list_for_each_entry_safe(brd, next, &brd_devices, brd_list)
brd_del_one(brd);