When copy-on-read is enabled it is necessary to wait for overlapping
requests before issuing new requests. This prevents races between the
copy-on-read and a write request.
Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
---
block.c | 39 +++++++++++++++++++++++++++++++++++++++
1 files changed, 39 insertions(+), 0 deletions(-)
diff --git a/block.c b/block.c
index e624ac3..cc3202c 100644
--- a/block.c
+++ b/block.c
@@ -1001,6 +1001,7 @@ struct BdrvTrackedRequest {
int nb_sectors;
bool is_write;
QLIST_ENTRY(BdrvTrackedRequest) list;
+ CoQueue wait_queue; /* coroutines blocked on this request */
};
/**
@@ -1014,6 +1015,12 @@ static void tracked_request_remove(BdrvTrackedRequest
*req)
{
if (req) {
QLIST_REMOVE(req, list);
+
+ /* Wake up all coroutines blocked on this request */
+ while (qemu_co_queue_next(&req->wait_queue)) {
+ /* Do nothing */
+ }
+
g_free(req);
}
}
@@ -1038,12 +1045,36 @@ static BdrvTrackedRequest
*tracked_request_add(BlockDriverState *bs,
req->sector_num = sector_num;
req->nb_sectors = nb_sectors;
req->is_write = is_write;
+ qemu_co_queue_init(&req->wait_queue);
QLIST_INSERT_HEAD(&bs->tracked_requests, req, list);
return req;
}
+static bool tracked_request_overlaps(BdrvTrackedRequest *req,
+ int64_t sector_num, int nb_sectors) {
+ return false; /* not yet implemented */
+}
+
+static void coroutine_fn wait_for_overlapping_requests(BlockDriverState *bs,
+ int64_t sector_num, int nb_sectors)
+{
+ BdrvTrackedRequest *req;
+ bool retry;
+
+ do {
+ retry = false;
+ QLIST_FOREACH(req, &bs->tracked_requests, list) {
+ if (tracked_request_overlaps(req, sector_num, nb_sectors)) {
+ qemu_co_queue_wait(&req->wait_queue);
+ retry = true;
+ break;
+ }
+ }
+ } while (retry);
+}
+
/**
* Enable tracking of incoming requests
*
@@ -1360,6 +1391,10 @@ static int coroutine_fn
bdrv_co_do_readv(BlockDriverState *bs,
return -EIO;
}
+ if (bs->copy_on_read) {
+ wait_for_overlapping_requests(bs, sector_num, nb_sectors);
+ }
+
req = tracked_request_add(bs, sector_num, nb_sectors, false);
ret = drv->bdrv_co_readv(bs, sector_num, nb_sectors, qiov);
tracked_request_remove(req);
@@ -1394,6 +1429,10 @@ static int coroutine_fn
bdrv_co_do_writev(BlockDriverState *bs,
return -EIO;
}
+ if (bs->copy_on_read) {
+ wait_for_overlapping_requests(bs, sector_num, nb_sectors);
+ }
+
req = tracked_request_add(bs, sector_num, nb_sectors, true);
ret = drv->bdrv_co_writev(bs, sector_num, nb_sectors, qiov);
--
1.7.6.3
