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Reuse the existing block layer infrastructure for serialising requests. Use the following approach: - mark ALLOCATE also SERIALISING, so subsequent requests to the area wait - ALLOCATE request itself must never wait if another request is in flight already. Return EAGAIN, let the caller reconsider. Signed-off-by: Anton Nefedov Reviewed-by: Alberto Garcia --- include/block/block.h | 3 +++ block/io.c | 31 ++++++++++++++++++++++++------- 2 files changed, 27 insertions(+), 7 deletions(-) diff --git a/include/block/block.h b/include/block/block.h index 643d32f4b8..dfc0fc1b8f 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -88,6 +88,9 @@ typedef enum { * efficiently allocate the space so it reads as zeroes, or return an error. * If this flag is set then BDRV_REQ_ZERO_WRITE must also be set. * This flag cannot be set together with BDRV_REQ_MAY_UNMAP. + * This flag implicitly sets BDRV_REQ_SERIALISING meaning it is protected + * from conflicts with overlapping requests. If such conflict is detected, + * -EAGAIN is returned. */ BDRV_REQ_ALLOCATE = 0x100, diff --git a/block/io.c b/block/io.c index 66006a089d..4451714a60 100644 --- a/block/io.c +++ b/block/io.c @@ -720,12 +720,13 @@ void bdrv_dec_in_flight(BlockDriverState *bs) bdrv_wakeup(bs); } -static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self) +static bool coroutine_fn find_or_wait_serialising_requests( + BdrvTrackedRequest *self, bool wait) { BlockDriverState *bs = self->bs; BdrvTrackedRequest *req; bool retry; - bool waited = false; + bool found = false; if (!atomic_read(&bs->serialising_in_flight)) { return false; @@ -751,11 +752,14 @@ static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self) * will wait for us as soon as it wakes up, then just go on * (instead of producing a deadlock in the former case). */ if (!req->waiting_for) { + found = true; + if (!wait) { + break; + } self->waiting_for = req; qemu_co_queue_wait(&req->wait_queue, &bs->reqs_lock); self->waiting_for = NULL; retry = true; - waited = true; break; } } @@ -763,7 +767,12 @@ static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self) qemu_co_mutex_unlock(&bs->reqs_lock); } while (retry); - return waited; + return found; +} + +static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self) +{ + return find_or_wait_serialising_requests(self, true); } static int bdrv_check_byte_request(BlockDriverState *bs, int64_t offset, @@ -1585,7 +1594,7 @@ bdrv_co_write_req_prepare(BdrvChild *child, int64_t offset, uint64_t bytes, BdrvTrackedRequest *req, int flags) { BlockDriverState *bs = child->bs; - bool waited; + bool found; int64_t end_sector = DIV_ROUND_UP(offset + bytes, BDRV_SECTOR_SIZE); if (bs->read_only) { @@ -1602,9 +1611,13 @@ bdrv_co_write_req_prepare(BdrvChild *child, int64_t offset, uint64_t bytes, mark_request_serialising(req, bdrv_get_cluster_size(bs)); } - waited = wait_serialising_requests(req); + found = find_or_wait_serialising_requests(req, + !(flags & BDRV_REQ_ALLOCATE)); + if (found && (flags & BDRV_REQ_ALLOCATE)) { + return -EAGAIN; + } - assert(!waited || !req->serialising || + assert(!found || !req->serialising || is_request_serialising_and_aligned(req)); assert(req->overlap_offset <= offset); assert(offset + bytes <= req->overlap_offset + req->overlap_bytes); @@ -1864,6 +1877,10 @@ int coroutine_fn bdrv_co_pwritev(BdrvChild *child, assert(!((flags & BDRV_REQ_ALLOCATE) && (flags & BDRV_REQ_MAY_UNMAP))); assert(!((flags & BDRV_REQ_ALLOCATE) && !(flags & BDRV_REQ_ZERO_WRITE))); + if (flags & BDRV_REQ_ALLOCATE) { + flags |= BDRV_REQ_SERIALISING; + } + trace_bdrv_co_pwritev(child->bs, offset, bytes, flags); if (!bs->drv) {