Drivers can have internal request sources that generates 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. Signed-off-by: Fam Zheng <f...@redhat.com> --- block/io.c | 3 +++ include/block/block_int.h | 6 ++++++ 2 files changed, 9 insertions(+) diff --git a/block/io.c b/block/io.c index b0dde7f..ad4b456 100644 --- a/block/io.c +++ b/block/io.c @@ -247,6 +247,9 @@ void bdrv_drain(BlockDriverState *bs) { bool busy = true; + if (bs->drv && bs->drv->bdrv_drain) { + bs->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 7c58221..99359b2 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -288,6 +288,12 @@ 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; }; -- 2.5.3