[Qemu-devel] [PATCH v2 3/6] qcow2: set L2 cache dependency in qcow2_alloc_bytes()

[Stefan Hajnoczi <stefanha@redhat.com>]

Compressed writes use qcow2_alloc_bytes() to allocate space with byte
granularity.  The affected clusters' refcounts will be incremented but
we do not need to flush yet.

Set a L2 cache dependency on the refcount block cache, so that the
refcounts get written out before the L2 updates.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/qcow2-refcount.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index e8b5d0a..4d9df5f 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -669,7 +669,11 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size)
         }
     }
 
-    bdrv_flush(bs->file);
+    /* The cluster refcount was incremented, either by qcow2_alloc_clusters()
+     * or explicitly by update_cluster_refcount().  Refcount blocks must be
+     * flushed before the caller's L2 table updates.
+     */
+    qcow2_cache_set_dependency(bs, s->l2_table_cache, s->refcount_block_cache);
     return offset;
 }
 
-- 
1.8.1.4