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[Qemu-devel] [RFC V6 29/33] qcow2: Do not overwrite existing entries wit
From: |
Benoît Canet |
Subject: |
[Qemu-devel] [RFC V6 29/33] qcow2: Do not overwrite existing entries with QCOW_OFLAG_COPIED. |
Date: |
Wed, 6 Feb 2013 13:32:02 +0100 |
In the case of a race condition between two writes a l2 entry can be written
without QCOW_OFLAG_COPIED before the first write fill it.
This patch simply check if the l2 entry has the correct offset without
QCOW_OFLAG_COPIED and do nothing.
Signed-off-by: Benoit Canet <address@hidden>
---
block/qcow2-cluster.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index fedcf57..c016e85 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -763,6 +763,11 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs,
QCowL2Meta *m)
for (i = 0; i < m->nb_clusters; i++) {
uint64_t flags = 0;
uint64_t offset = cluster_offset + (i << s->cluster_bits);
+
+ if (be64_to_cpu(l2_table[l2_index + i]) == offset) {
+ continue;
+ }
+
/* if two concurrent writes happen to the same unallocated cluster
* each write allocates separate cluster and writes data concurrently.
* The first one to complete updates l2 table with pointer to its
--
1.7.10.4
- [Qemu-devel] [RFC V6 27/33] qcow2: Adapt checking of QCOW_OFLAG_COPIED for dedup., (continued)
- [Qemu-devel] [RFC V6 07/33] qcow2: Add qcow2_dedup and related functions, Benoît Canet, 2013/02/06
- [Qemu-devel] [RFC V6 13/33] qcow2: make the deduplication forget a cluster hash when a cluster is to dedupe, Benoît Canet, 2013/02/06
- [Qemu-devel] [RFC V6 29/33] qcow2: Do not overwrite existing entries with QCOW_OFLAG_COPIED.,
Benoît Canet <=
- [Qemu-devel] [RFC V6 26/33] qcow2: Add verification of dedup table., Benoît Canet, 2013/02/06
- [Qemu-devel] [RFC V6 23/33] qcow2: Add qcow2_dedup_is_running to probe if dedup is running., Benoît Canet, 2013/02/06
- [Qemu-devel] [RFC V6 24/33] qcow2: Integrate deduplication in qcow2_co_writev loop., Benoît Canet, 2013/02/06
[Qemu-devel] [RFC V6 14/33] qcow2: Create qcow2_is_cluster_to_dedup., Benoît Canet, 2013/02/06