The idea is that ALLOCATE requests may overlap with other requests.
Reuse the existing block layer infrastructure for serialising requests.
Use the following approach:
- mark ALLOCATE 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 <anton.nefe...@virtuozzo.com>
---
block/io.c | 27 +++++++++++++++++++--------
1 file changed, 19 insertions(+), 8 deletions(-)
diff --git a/block/io.c b/block/io.c
index 7506207..1e07a0b 100644
--- a/block/io.c
+++ b/block/io.c
@@ -535,7 +535,8 @@ void bdrv_dec_in_flight(BlockDriverState *bs)
bdrv_wakeup(bs);
}
-static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self)
+static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self,
+ bool nowait)
{
BlockDriverState *bs = self->bs;
BdrvTrackedRequest *req;
@@ -566,11 +567,14 @@ 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) {
+ waited = true;
+ if (nowait) {
+ break;
+ }
self->waiting_for = req;
qemu_co_queue_wait(&req->wait_queue, &bs->reqs_lock);
self->waiting_for = NULL;
retry = true;
- waited = true;
break;
}
}
@@ -1120,7 +1124,7 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild
*child,
}
if (!(flags & BDRV_REQ_NO_SERIALISING)) {
- wait_serialising_requests(req);
+ wait_serialising_requests(req, false);
}
if (flags & BDRV_REQ_COPY_ON_READ) {
@@ -1410,7 +1414,10 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild
*child,
max_transfer = QEMU_ALIGN_DOWN(MIN_NON_ZERO(bs->bl.max_transfer, INT_MAX),
align);
- waited = wait_serialising_requests(req);
+ waited = wait_serialising_requests(req, flags & BDRV_REQ_ALLOCATE);
+ if (waited && flags & BDRV_REQ_ALLOCATE) {
+ return -EAGAIN;
+ }
assert(!waited || !req->serialising);
assert(req->overlap_offset <= offset);
assert(offset + bytes <= req->overlap_offset + req->overlap_bytes);
@@ -1514,7 +1521,7 @@ static int coroutine_fn bdrv_co_do_zero_pwritev(BdrvChild
*child,
/* RMW the unaligned part before head. */
mark_request_serialising(req, align);
- wait_serialising_requests(req);
+ wait_serialising_requests(req, false);
bdrv_debug_event(bs, BLKDBG_PWRITEV_RMW_HEAD);
ret = bdrv_aligned_preadv(child, req, offset & ~(align - 1), align,
align, &local_qiov, 0);
@@ -1534,6 +1541,10 @@ static int coroutine_fn
bdrv_co_do_zero_pwritev(BdrvChild *child,
bytes -= zero_bytes;
}
+ if (flags & BDRV_REQ_ALLOCATE) {
+ mark_request_serialising(req, align);
+ }
+
assert(!bytes || (offset & (align - 1)) == 0);
if (bytes >= align) {
/* Write the aligned part in the middle. */
@@ -1552,7 +1563,7 @@ static int coroutine_fn bdrv_co_do_zero_pwritev(BdrvChild
*child,
assert(align == tail_padding_bytes + bytes);
/* RMW the unaligned part after tail. */
mark_request_serialising(req, align);
- wait_serialising_requests(req);
+ wait_serialising_requests(req, false);
bdrv_debug_event(bs, BLKDBG_PWRITEV_RMW_TAIL);
ret = bdrv_aligned_preadv(child, req, offset, align,
align, &local_qiov, 0);
@@ -1623,7 +1634,7 @@ int coroutine_fn bdrv_co_pwritev(BdrvChild *child,
struct iovec head_iov;
mark_request_serialising(&req, align);
- wait_serialising_requests(&req);
+ wait_serialising_requests(&req, false);
head_buf = qemu_blockalign(bs, align);
head_iov = (struct iovec) {
@@ -1664,7 +1675,7 @@ int coroutine_fn bdrv_co_pwritev(BdrvChild *child,
bool waited;
mark_request_serialising(&req, align);
- waited = wait_serialising_requests(&req);
+ waited = wait_serialising_requests(&req, false);
assert(!waited || !use_local_qiov);
tail_buf = qemu_blockalign(bs, align);
--
2.7.4
