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[Qemu-devel] [PATCH] qcow2: Remove unnecessary flush after L2 write
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PATCH] qcow2: Remove unnecessary flush after L2 write |
Date: |
Wed, 1 Sep 2010 14:14:32 +0200 |
When a new cluster was allocated, we only need a flush after the write to the
L2 table if it was a COW and we need to decrease the refcounts of the old
clusters.
Signed-off-by: Kevin Wolf <address@hidden>
---
block/qcow2-cluster.c | 16 ++++++++++++----
1 files changed, 12 insertions(+), 4 deletions(-)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index b023148..0ce24d6 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -656,7 +656,7 @@ static int write_l2_entries(BlockDriverState *bs, uint64_t
*l2_table,
int ret;
BLKDBG_EVENT(bs->file, BLKDBG_L2_UPDATE);
- ret = bdrv_pwrite_sync(bs->file, l2_offset + start_offset,
+ ret = bdrv_pwrite(bs->file, l2_offset + start_offset,
&l2_table[l2_start_index], len);
if (ret < 0) {
return ret;
@@ -719,9 +719,17 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs,
QCowL2Meta *m)
goto err;
}
- for (i = 0; i < j; i++)
- qcow2_free_any_clusters(bs,
- be64_to_cpu(old_cluster[i]) & ~QCOW_OFLAG_COPIED, 1);
+ /*
+ * If this was a COW, we need to decrease the refcount of the old cluster.
+ * Also flush bs->file to get the right order for L2 and refcount update.
+ */
+ if (j != 0) {
+ bdrv_flush(bs->file);
+ for (i = 0; i < j; i++) {
+ qcow2_free_any_clusters(bs,
+ be64_to_cpu(old_cluster[i]) & ~QCOW_OFLAG_COPIED, 1);
+ }
+ }
ret = 0;
err:
--
1.7.2.2
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