On Mon, Oct 17, 2011 at 11:47 PM, Stefan Hajnoczi <stefa...@linux.vnet.ibm.com> wrote: > 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 <stefa...@linux.vnet.ibm.com> > --- > block.c | 39 +++++++++++++++++++++++++++++++++++++-- > 1 files changed, 37 insertions(+), 2 deletions(-) > > diff --git a/block.c b/block.c > index cc3202c..0c22741 100644 > --- a/block.c > +++ b/block.c > @@ -1052,21 +1052,56 @@ static BdrvTrackedRequest > *tracked_request_add(BlockDriverState *bs, > return req; > } > > +/** > + * 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 = (sector_num / c) * c; I can understand the above formula, but the one below is very magic. :) and can not be understood by me. > + *cluster_nb_sectors = ((sector_num % c) + nb_sectors + c - 1) / c * > 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 */ > + 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; > -- > 1.7.6.3 > > > -- Regards, Zhi Yong Wu