[Qemu-devel] [PATCH v2 09/20] block drivers: expose requirement for write same alignment from formats

[Paolo Bonzini <pbonzini@redhat.com>]

This will let misaligned but large requests use zero clusters.  This
is important because the cluster size is not guest visible.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block/qcow2.c | 1 +
 block/qed.c   | 1 +
 block/vmdk.c  | 4 ++++
 3 files changed, 6 insertions(+)

diff --git a/block/qcow2.c b/block/qcow2.c
index 92ed895..9cc247b 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -718,6 +718,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     qemu_opts_del(opts);
+    bs->bl.write_zeroes_alignment = s->cluster_sectors;
 
     if (s->use_lazy_refcounts && s->qcow_version < 3) {
         error_setg(errp, "Lazy refcounts require a qcow2 image with at least "
diff --git a/block/qed.c b/block/qed.c
index 1f87420..23247f3 100644
--- a/block/qed.c
+++ b/block/qed.c
@@ -495,6 +495,7 @@ static int bdrv_qed_open(BlockDriverState *bs, QDict *options, int flags,
         }
     }
 
+    bs->bl.write_zeroes_alignment = s->header.cluster_size >> BDRV_SECTOR_BITS;
     s->need_check_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
                                             qed_need_check_timer_cb, s);
 
diff --git a/block/vmdk.c b/block/vmdk.c
index 6555663..63ea7ff 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -428,6 +428,10 @@ static int vmdk_add_extent(BlockDriverState *bs,
     extent->l2_size = l2_size;
     extent->cluster_sectors = flat ? sectors : cluster_sectors;
 
+    if (!flat) {
+        bs->bl.write_zeroes_alignment =
+            MAX(bs->bl.write_zeroes_alignment, cluster_sectors);
+    }
     if (s->num_extents > 1) {
         extent->end_sector = (*(extent - 1)).end_sector + extent->sectors;
     } else {
-- 
1.8.4.2