qcow2: Zero write support
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 5e5f5cf..a747a88 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1102,3 +1102,75 @@
return 0;
}
+
+/*
+ * This zeroes as many clusters of nb_clusters as possible at once (i.e.
+ * all clusters in the same L2 table) and returns the number of zeroed
+ * clusters.
+ */
+static int zero_single_l2(BlockDriverState *bs, uint64_t offset,
+ unsigned int nb_clusters)
+{
+ BDRVQcowState *s = bs->opaque;
+ uint64_t *l2_table;
+ int l2_index;
+ int ret;
+ int i;
+
+ ret = get_cluster_table(bs, offset, &l2_table, &l2_index);
+ if (ret < 0) {
+ return ret;
+ }
+
+ /* Limit nb_clusters to one L2 table */
+ nb_clusters = MIN(nb_clusters, s->l2_size - l2_index);
+
+ for (i = 0; i < nb_clusters; i++) {
+ uint64_t old_offset;
+
+ old_offset = be64_to_cpu(l2_table[l2_index + i]);
+
+ /* Update L2 entries */
+ qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);
+ if (old_offset & QCOW_OFLAG_COMPRESSED) {
+ l2_table[l2_index + i] = cpu_to_be64(QCOW_OFLAG_ZERO);
+ qcow2_free_any_clusters(bs, old_offset, 1);
+ } else {
+ l2_table[l2_index + i] |= cpu_to_be64(QCOW_OFLAG_ZERO);
+ }
+ }
+
+ ret = qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);
+ if (ret < 0) {
+ return ret;
+ }
+
+ return nb_clusters;
+}
+
+int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors)
+{
+ BDRVQcowState *s = bs->opaque;
+ unsigned int nb_clusters;
+ int ret;
+
+ /* The zero flag is only supported by version 3 and newer */
+ if (s->qcow_version < 3) {
+ return -ENOTSUP;
+ }
+
+ /* Each L2 table is handled by its own loop iteration */
+ nb_clusters = size_to_clusters(s, nb_sectors << BDRV_SECTOR_BITS);
+
+ while (nb_clusters > 0) {
+ ret = zero_single_l2(bs, offset, nb_clusters);
+ if (ret < 0) {
+ return ret;
+ }
+
+ nb_clusters -= ret;
+ offset += (ret * s->cluster_size);
+ }
+
+ return 0;
+}
diff --git a/block/qcow2.c b/block/qcow2.c
index 41b195d..ad46c03 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1281,6 +1281,26 @@
return 0;
}
+static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs,
+ int64_t sector_num, int nb_sectors)
+{
+ int ret;
+ BDRVQcowState *s = bs->opaque;
+
+ /* Emulate misaligned zero writes */
+ if (sector_num % s->cluster_sectors || nb_sectors % s->cluster_sectors) {
+ return -ENOTSUP;
+ }
+
+ /* Whatever is left can use real zero clusters */
+ qemu_co_mutex_lock(&s->lock);
+ ret = qcow2_zero_clusters(bs, sector_num << BDRV_SECTOR_BITS,
+ nb_sectors);
+ qemu_co_mutex_unlock(&s->lock);
+
+ return ret;
+}
+
static coroutine_fn int qcow2_co_discard(BlockDriverState *bs,
int64_t sector_num, int nb_sectors)
{
@@ -1558,6 +1578,7 @@
.bdrv_co_writev = qcow2_co_writev,
.bdrv_co_flush_to_os = qcow2_co_flush_to_os,
+ .bdrv_co_write_zeroes = qcow2_co_write_zeroes,
.bdrv_co_discard = qcow2_co_discard,
.bdrv_truncate = qcow2_truncate,
.bdrv_write_compressed = qcow2_write_compressed,
diff --git a/block/qcow2.h b/block/qcow2.h
index 2a98244..93567f6 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -283,6 +283,7 @@
int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m);
int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset,
int nb_sectors);
+int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors);
/* qcow2-snapshot.c functions */
int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info);
