tree 38b95ac286ddedae55d3b540c0a52db6c1b6984f
parent 7a6ab45e19b615b9285b9cfa2bbc1fee012bc8d7
author Kevin Wolf <kwolf@redhat.com> 1506084612 +0200
committer Kevin Wolf <kwolf@redhat.com> 1506429983 +0200

qemu-io: Drop write permissions before read-only reopen

qemu-io provides a 'reopen' command that allows switching from writable
to read-only access. We need to make sure that we don't try to keep
write permissions to a BlockBackend that becomes read-only, otherwise
things are going to fail.

This requires a bdrv_drain() call because otherwise in-flight AIO
write requests could issue new internal requests while the permission
has already gone away, which would cause assertion failures. Draining
the queue doesn't break AIO requests in any new way, bdrv_reopen() would
drain it anyway only a few lines later.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>