static bool bdrv_drain_recurse(BlockDriverState *bs, bool begin) { BdrvChild *child, *tmp; bool waited; /* Ensure any pending metadata writes are submitted to bs->file. */ bdrv_drain_invoke(bs, begin); /* Wait for drained requests to finish */ waited = BDRV_POLL_WHILE(bs, atomic_read(&bs->in_flight) > 0); QLIST_FOREACH_SAFE(child, &bs->children, next, tmp) { BlockDriverState *bs = child->bs; bool in_main_loop = qemu_get_current_aio_context() == qemu_get_aio_context(); assert(bs->refcnt > 0); if (in_main_loop) { /* In case the recursive bdrv_drain_recurse processes a * block_job_defer_to_main_loop BH and modifies the graph, * let's hold a reference to bs until we are done. * * IOThread doesn't have such a BH, and it is not safe to call * bdrv_unref without BQL, so skip doing it there. */ bdrv_ref(bs); } waited |= bdrv_drain_recurse(bs, begin); if (in_main_loop) { bdrv_unref(bs); } } return waited; }