On 04/11/2018 11:39 AM, Kevin Wolf wrote:
> All involved nodes are already idle, we called bdrv_do_draine_begin() on


> them.
> The comment in the code suggested that this were not correct because the


> completion of a request on one node could spawn a new request on a
> different node (which might have been drained before, so we wouldn't
> drain the new request). In reality, new requests to different nodes
> aren't spawned out of nothing, but only in the context of a parent
> request, and they aren't submitted to random nodes, but only to child
> nodes. As long as we still poll for the completion of the parent request
> (which we do), draining each root node separately is good enough.
> Remove the additional polling code from bdrv_drain_all_begin() and
> replace it with an assertion that all nodes are already idle after we
> drained them separately.
> Signed-off-by: Kevin Wolf <kw...@redhat.com>
> ---
>  block/io.c | 41 ++++++++++++-----------------------------
>  1 file changed, 12 insertions(+), 29 deletions(-)

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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