On 09/11/2015 11:16, Fam Zheng wrote: > 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.
Reviewed-by: Paolo Bonzini <pbonz...@redhat.com> > Signed-off-by: Fam Zheng <f...@redhat.com> > --- > block/io.c | 16 +++++++++++++++- > include/block/block_int.h | 6 ++++++ > 2 files changed, 21 insertions(+), 1 deletion(-) > > diff --git a/block/io.c b/block/io.c > index 4ecb171..adc1eab 100644 > --- a/block/io.c > +++ b/block/io.c > @@ -237,8 +237,21 @@ bool bdrv_requests_pending(BlockDriverState *bs) > return false; > } > > +static void bdrv_drain_recurse(BlockDriverState *bs) > +{ > + BdrvChild *child; > + > + if (bs->drv && bs->drv->bdrv_drain) { > + bs->drv->bdrv_drain(bs); > + } > + QLIST_FOREACH(child, &bs->children, next) { > + bdrv_drain_recurse(child->bs); > + } > +} > + > /* > - * Wait for pending requests to complete on a single BlockDriverState subtree > + * Wait for pending requests to complete on a single BlockDriverState > subtree, > + * and suspend block driver's internal I/O until next request arrives. > * > * Note that unlike bdrv_drain_all(), the caller must hold the > BlockDriverState > * AioContext. > @@ -251,6 +264,7 @@ void bdrv_drain(BlockDriverState *bs) > { > bool busy = true; > > + bdrv_drain_recurse(bs); > while (busy) { > /* Keep iterating */ > bdrv_flush_io_queue(bs); > diff --git a/include/block/block_int.h b/include/block/block_int.h > index 550ce18..4a9f8ff 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -295,6 +295,12 @@ struct BlockDriver { > */ > int (*bdrv_probe_geometry)(BlockDriverState *bs, HDGeometry *geo); > > + /** > + * Drain and stop any internal sources of requests in the driver, and > + * remain so until next I/O callback (e.g. bdrv_co_writev) is called. > + */ > + void (*bdrv_drain)(BlockDriverState *bs); > + > QLIST_ENTRY(BlockDriver) list; > }; > >