Patchwork [4/4] qcow2: Get rid of additional sync on COW

login
register
mail settings
Submitter Kevin Wolf
Date Sept. 17, 2010, 4:18 p.m.
Message ID <1284740318-20838-5-git-send-email-kwolf@redhat.com>
Download mbox | patch
Permalink /patch/65093/
State New
Headers show

Comments

Kevin Wolf - Sept. 17, 2010, 4:18 p.m.
We always have a sync for the refcount update when a new cluster is
allocated. If we move this past the COW, we can save an additional sync.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2-cluster.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

Patch

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 66969c2..634ccef 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -422,7 +422,7 @@  static int copy_sectors(BlockDriverState *bs, uint64_t start_sect,
                         &s->aes_encrypt_key);
     }
     BLKDBG_EVENT(bs->file, BLKDBG_COW_WRITE);
-    ret = bdrv_write_sync(bs->file, (cluster_offset >> 9) + n_start,
+    ret = bdrv_write(bs->file, (cluster_offset >> 9) + n_start,
         s->cluster_data, n);
     if (ret < 0)
         return ret;
@@ -721,6 +721,13 @@  int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
                     (i << s->cluster_bits)) | QCOW_OFLAG_COPIED);
      }
 
+    /*
+     * Before we update the L2 table to actually point to the new cluster, we
+     * need to be sure that the refcounts have been increased and COW was
+     * handled.
+     */
+    bdrv_flush(bs->file);
+
     ret = write_l2_entries(bs, l2_table, l2_offset, l2_index, m->nb_clusters);
     if (ret < 0) {
         qcow2_l2_cache_reset(bs);
@@ -872,7 +879,6 @@  int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
         QLIST_REMOVE(m, next_in_flight);
         return cluster_offset;
     }
-    bdrv_flush(bs->file);
 
     /* save info needed for meta data update */
     m->offset = offset;