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 <f...@redhat.com> --- block/io.c | 13 ++++++++++++- include/block/block_int.h | 6 ++++++ 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/block/io.c b/block/io.c index 4ecb171..136849c 100644 --- a/block/io.c +++ b/block/io.c @@ -238,7 +238,8 @@ bool bdrv_requests_pending(BlockDriverState *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. @@ -249,8 +250,18 @@ bool bdrv_requests_pending(BlockDriverState *bs) */ void bdrv_drain(BlockDriverState *bs) { + BdrvChild *child; bool busy = true; + if (bs->drv && bs->drv->bdrv_drain) { + bs->drv->bdrv_drain(bs); + } + QLIST_FOREACH(child, &bs->children, next) { + BlockDriverState *cbs = child->bs; + if (cbs->drv && cbs->drv->bdrv_drain) { + cbs->drv->bdrv_drain(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; }; -- 2.4.3