Linux block devices can be set read-only with "blockdev --setro
<device>". The same thing can be done for LVM volumes using "lvchange
--permission r <volume>". This read-only setting is independent of
device node permissions. Therefore the device can still be opened
O_RDWR but actual writes will fail.
This results in odd behavior for QEMU. bdrv_open() is supposed to fail
if a read-only image is being opened with BDRV_O_RDWR. By not failing
for Linux block devices, the guest boots up but every write produces an
I/O error.
This patch checks whether the block device is read-only so that Linux
block devices behave like regular files.
Reported-by: Sibiao Luo <sluo@redhat.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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