block: Make overlap range for serialisation dynamic
Copy on Read wants to serialise with all requests touching the same
cluster, so wait_serialising_requests() rounded to cluster boundaries.
Other users like alignment RMW will have different requirements, though
(requests touching the same sector), so make it dynamic.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
diff --git a/block.c b/block.c
index 493c75f..784ff07 100644
--- a/block.c
+++ b/block.c
@@ -2231,6 +2231,8 @@
.is_write = is_write,
.co = qemu_coroutine_self(),
.serialising = false,
+ .overlap_offset = offset,
+ .overlap_bytes = bytes,
};
qemu_co_queue_init(&req->wait_queue);
@@ -2238,12 +2240,19 @@
QLIST_INSERT_HEAD(&bs->tracked_requests, req, list);
}
-static void mark_request_serialising(BdrvTrackedRequest *req)
+static void mark_request_serialising(BdrvTrackedRequest *req, size_t align)
{
+ int64_t overlap_offset = req->offset & ~(align - 1);
+ int overlap_bytes = ROUND_UP(req->offset + req->bytes, align)
+ - overlap_offset;
+
if (!req->serialising) {
req->bs->serialising_in_flight++;
req->serialising = true;
}
+
+ req->overlap_offset = MIN(req->overlap_offset, overlap_offset);
+ req->overlap_bytes = MAX(req->overlap_bytes, overlap_bytes);
}
/**
@@ -2267,20 +2276,16 @@
}
}
-static void round_bytes_to_clusters(BlockDriverState *bs,
- int64_t offset, unsigned int bytes,
- int64_t *cluster_offset,
- unsigned int *cluster_bytes)
+static int bdrv_get_cluster_size(BlockDriverState *bs)
{
BlockDriverInfo bdi;
+ int ret;
- if (bdrv_get_info(bs, &bdi) < 0 || bdi.cluster_size == 0) {
- *cluster_offset = offset;
- *cluster_bytes = bytes;
+ ret = bdrv_get_info(bs, &bdi);
+ if (ret < 0 || bdi.cluster_size == 0) {
+ return bs->request_alignment;
} else {
- *cluster_offset = QEMU_ALIGN_DOWN(offset, bdi.cluster_size);
- *cluster_bytes = QEMU_ALIGN_UP(offset - *cluster_offset + bytes,
- bdi.cluster_size);
+ return bdi.cluster_size;
}
}
@@ -2288,11 +2293,11 @@
int64_t offset, unsigned int bytes)
{
/* aaaa bbbb */
- if (offset >= req->offset + req->bytes) {
+ if (offset >= req->overlap_offset + req->overlap_bytes) {
return false;
}
/* bbbb aaaa */
- if (req->offset >= offset + bytes) {
+ if (req->overlap_offset >= offset + bytes) {
return false;
}
return true;
@@ -2302,30 +2307,21 @@
{
BlockDriverState *bs = self->bs;
BdrvTrackedRequest *req;
- int64_t cluster_offset;
- unsigned int cluster_bytes;
bool retry;
if (!bs->serialising_in_flight) {
return;
}
- /* If we touch the same cluster it counts as an overlap. This guarantees
- * that allocating writes will be serialized and not race with each other
- * for the same cluster. For example, in copy-on-read it ensures that the
- * CoR read and write operations are atomic and guest writes cannot
- * interleave between them.
- */
- round_bytes_to_clusters(bs, self->offset, self->bytes,
- &cluster_offset, &cluster_bytes);
-
do {
retry = false;
QLIST_FOREACH(req, &bs->tracked_requests, list) {
if (req == self || (!req->serialising && !self->serialising)) {
continue;
}
- if (tracked_request_overlaps(req, cluster_offset, cluster_bytes)) {
+ if (tracked_request_overlaps(req, self->overlap_offset,
+ self->overlap_bytes))
+ {
/* Hitting this means there was a reentrant request, for
* example, a block driver issuing nested requests. This must
* never happen since it means deadlock.
@@ -2941,7 +2937,12 @@
/* Handle Copy on Read and associated serialisation */
if (flags & BDRV_REQ_COPY_ON_READ) {
- mark_request_serialising(req);
+ /* If we touch the same cluster it counts as an overlap. This
+ * guarantees that allocating writes will be serialized and not race
+ * with each other for the same cluster. For example, in copy-on-read
+ * it ensures that the CoR read and write operations are atomic and
+ * guest writes cannot interleave between them. */
+ mark_request_serialising(req, bdrv_get_cluster_size(bs));
}
wait_serialising_requests(req);
