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block: request overlap detection 

Detect overlapping requests and remember to align to cluster boundaries
if the image format uses them.  This assumes that allocating I/O is
performed in cluster granularity - which is true for qcow2, qed, etc.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2011-11-23 11:47:56 +00:00 committed by Kevin Wolf
parent f4658285f9
commit d83947ac6d
1 changed files with 43 additions and 2 deletions
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45
block.c
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@ -1133,21 +1133,62 @@ static void tracked_request_begin(BdrvTrackedRequest *req,
QLIST_INSERT_HEAD(&bs->tracked_requests, req, list);
}
/**
* Round a region to cluster boundaries
*/
static void round_to_clusters(BlockDriverState *bs,
int64_t sector_num, int nb_sectors,
int64_t *cluster_sector_num,
int *cluster_nb_sectors)
{
BlockDriverInfo bdi;
if (bdrv_get_info(bs, &bdi) < 0 || bdi.cluster_size == 0) {
*cluster_sector_num = sector_num;
*cluster_nb_sectors = nb_sectors;
} else {
int64_t c = bdi.cluster_size / BDRV_SECTOR_SIZE;
*cluster_sector_num = QEMU_ALIGN_DOWN(sector_num, c);
*cluster_nb_sectors = QEMU_ALIGN_UP(sector_num - *cluster_sector_num +
nb_sectors, c);
}
}
static bool tracked_request_overlaps(BdrvTrackedRequest *req,
int64_t sector_num, int nb_sectors) {
return false; /* not yet implemented */
/* aaaa bbbb */
if (sector_num >= req->sector_num + req->nb_sectors) {
return false;
}
/* bbbb aaaa */
if (req->sector_num >= sector_num + nb_sectors) {
return false;
}
return true;
}
static void coroutine_fn wait_for_overlapping_requests(BlockDriverState *bs,
int64_t sector_num, int nb_sectors)
{
BdrvTrackedRequest *req;
int64_t cluster_sector_num;
int cluster_nb_sectors;
bool retry;
/* 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_to_clusters(bs, sector_num, nb_sectors,
&cluster_sector_num, &cluster_nb_sectors);
do {
retry = false;
QLIST_FOREACH(req, &bs->tracked_requests, list) {
if (tracked_request_overlaps(req, sector_num, nb_sectors)) {
if (tracked_request_overlaps(req, cluster_sector_num,
cluster_nb_sectors)) {
qemu_co_queue_wait(&req->wait_queue);
retry = true;
break;