On Wed, 03/16 15:16, Paolo Bonzini wrote: > bdrv_requests_pending is checking children to also wait until internal > requests (such as metadata writes) have completed. However, checking > children is in general overkill. Children requests can be of two kinds: > > - requests caused by an operation on bs, e.g. a bdrv_aio_write to bs > causing a write to bs->file->bs. In this case, the parent's in_flight > count will always be incremented by at least one for every request in > the child. > > - asynchronous metadata writes or flushes. Such writes can be started > even if bs's in_flight count is zero, but not after the .bdrv_drain > callback has been invoked. > > This patch therefore changes bdrv_drain to finish I/O in the parent > (after which the parent's in_flight will be locked to zero), call > bdrv_drain (after which the parent will not generate I/O on the child > anymore), and then wait for internal I/O in the children to complete. > > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> > --- > v1->v2: moved bdrv_drain callback after in_flight is 0 > in the parent [from QED drain discussion]
This is nice! Reviewed-by: Fam Zheng <f...@redhat.com>
