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authorEric Blake <eblake@redhat.com>2019-01-17 13:36:57 -0600
committerEric Blake <eblake@redhat.com>2019-01-21 15:49:52 -0600
commit7c6f5ddca62905e67025aa0657e8a011cbdffa11 (patch)
tree3265f47024862755978ed6054486d78e95878794 /qemu-nbd.texi
parent68b96f15838d309ef791cb83b5eec1bd7da271c2 (diff)
nbd/client: Work around 3.0 bug for listing meta contexts
Commit 3d068aff forgot to advertise available qemu: contexts when the client requests a list with 0 queries. Furthermore, 3.0 shipped with a qemu-img hack of x-dirty-bitmap (commit 216ee365) that _silently_ acts as though the entire image is clean if a requested bitmap is not present. Both bugs have been recently fixed, so that a modern qemu server gives full context output right away, and the client refuses a connection if a requested x-dirty-bitmap was not found. Still, it is likely that there will be users that have to work with a mix of old and new qemu versions, depending on which features get backported where, at which point being able to rely on 'qemu-img --list' output to know for sure whether a given NBD export has the desired dirty bitmap is much nicer than blindly connecting and risking that the entire image may appear clean. We can make our --list code smart enough to work around buggy servers by tracking whether we've seen any qemu: replies in the original 0-query list; if not, repeat with a single query on "qemu:" (which may still have no replies, but then we know for sure we didn't trip up on the server bug). Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20190117193658.16413-21-eblake@redhat.com>
Diffstat (limited to 'qemu-nbd.texi')
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