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Subjectblock device read-only handling regression in 2.6.38-rc4 (bisected)
Hi Tejun,

Seems this commit cause regressions:

commit 75f1dc0d076d1c1168f2115f1941ea627d38bd5a
Author: Tejun Heo <>
Date: Sat Nov 13 11:55:17 2010 +0100

block: check bdev_read_only() from blkdev_get()

bdev read-only status can be queried using bdev_read_only() and may
change while the device is being opened. Enforce it by checking it
from blkdev_get() after open succeeds.

1) loop device once set read-only is not able to be used read-write afterward

touch /x1.img
losetup -r /dev/loop0 /x1.img
losetup -d /dev/loop0
losetup /dev/loop0 /x1.img
/dev/loop0: Permission denied

2) it breaks read-only dm-snapshots
(Fedora LiveCD operations is broken by this as well.)

(x.img is backing device, xs.img is prepared COW, you can simply run it
once in read-write to create dm-snap header and then re-run this commands)

losetup -r /dev/loop0 /x.img
losetup -r /dev/loop1 /xs.img
dmsetup create x --readonly --table '0 131072 snapshot /dev/loop0 /dev/loop1 p 8'
device-mapper: reload ioctl failed: Permission denied


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