tree c28226815e2d495cee3106dcf557667751adec10
parent 83c98d7b924eab36a0a2c7813731dbef439a91d3
author Fam Zheng <famz@redhat.com> 1447064213 +0800
committer Kevin Wolf <kwolf@redhat.com> 1447341763 +0100

block: Introduce BlockDriver.bdrv_drain callback

Drivers can have internal request sources that generate IO, like the
need_check_timer in QED. Since we want quiesced periods that contain
nested event loops in block layer, we need to have a way to disable such
event sources.

Block drivers must implement the "bdrv_drain" callback if it has any
internal sources that can generate I/O activity, like a timer or a
worker thread (even in a library) that can schedule QEMUBH in an
asynchronous callback.

Update the comments of bdrv_drain and bdrv_drained_begin accordingly.

Like bdrv_requests_pending(), we should consider all the children of bs.
Before, the while loop just works, as bdrv_requests_pending() already
tracks its children; now we mustn't miss the callback, so recurse down
explicitly.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1447064214-29930-9-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>