diff options
Diffstat (limited to 'block/qcow2.c')
| -rw-r--r-- | block/qcow2.c | 64 |
1 files changed, 54 insertions, 10 deletions
diff --git a/block/qcow2.c b/block/qcow2.c index b3ba5daa93..328b1d4fb5 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -1575,6 +1575,44 @@ fail: return ret; } +/* Check if it's possible to merge a write request with the writing of + * the data from the COW regions */ +static bool merge_cow(uint64_t offset, unsigned bytes, + QEMUIOVector *hd_qiov, QCowL2Meta *l2meta) +{ + QCowL2Meta *m; + + for (m = l2meta; m != NULL; m = m->next) { + /* If both COW regions are empty then there's nothing to merge */ + if (m->cow_start.nb_bytes == 0 && m->cow_end.nb_bytes == 0) { + continue; + } + + /* The data (middle) region must be immediately after the + * start region */ + if (l2meta_cow_start(m) + m->cow_start.nb_bytes != offset) { + continue; + } + + /* The end region must be immediately after the data (middle) + * region */ + if (m->offset + m->cow_end.offset != offset + bytes) { + continue; + } + + /* Make sure that adding both COW regions to the QEMUIOVector + * does not exceed IOV_MAX */ + if (hd_qiov->niov > IOV_MAX - 2) { + continue; + } + + m->data_qiov = hd_qiov; + return true; + } + + return false; +} + static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags) @@ -1657,16 +1695,22 @@ static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset, goto fail; } - qemu_co_mutex_unlock(&s->lock); - BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO); - trace_qcow2_writev_data(qemu_coroutine_self(), - cluster_offset + offset_in_cluster); - ret = bdrv_co_pwritev(bs->file, - cluster_offset + offset_in_cluster, - cur_bytes, &hd_qiov, 0); - qemu_co_mutex_lock(&s->lock); - if (ret < 0) { - goto fail; + /* If we need to do COW, check if it's possible to merge the + * writing of the guest data together with that of the COW regions. + * If it's not possible (or not necessary) then write the + * guest data now. */ + if (!merge_cow(offset, cur_bytes, &hd_qiov, l2meta)) { + qemu_co_mutex_unlock(&s->lock); + BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO); + trace_qcow2_writev_data(qemu_coroutine_self(), + cluster_offset + offset_in_cluster); + ret = bdrv_co_pwritev(bs->file, + cluster_offset + offset_in_cluster, + cur_bytes, &hd_qiov, 0); + qemu_co_mutex_lock(&s->lock); + if (ret < 0) { + goto fail; + } } while (l2meta != NULL) { |