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| author | Kevin Wolf <kwolf@redhat.com> | 2011-02-09 17:36:19 +0100 |
|---|---|---|
| committer | Kevin Wolf <kwolf@redhat.com> | 2011-02-11 14:34:06 +0100 |
| commit | c7e9df3bc6bf0cad74081c7492b5aab753bf9cc9 (patch) | |
| tree | af1aaeba15d175ac54794dc13d21609f875dfac2 | |
| parent | 038a866f8153c45499b80162f8e1b7188620bd8a (diff) | |
| download | qemu-c7e9df3bc6bf0cad74081c7492b5aab753bf9cc9.tar.gz | |
qcow2: Fix order in L2 table COW
When copying L2 tables (this happens only with internal snapshots), the order
wasn't completely safe, so that after a crash you could end up with a L2 table
that has too low refcount, possibly leading to corruption in the long run.
This patch puts the operations in the right order: First allocate the new
L2 table and replace the reference, and only then decrease the refcount of the
old table.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 16fde5f2c2788232b16c06d34d0459a5c1ec1f6c)
| -rw-r--r-- | block/qcow2-cluster.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 437aaa8174..750abe37d4 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -515,13 +515,16 @@ static int get_cluster_table(BlockDriverState *bs, uint64_t offset, return ret; } } else { - /* FIXME Order */ - if (l2_offset) - qcow2_free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t)); + /* First allocate a new L2 table (and do COW if needed) */ ret = l2_allocate(bs, l1_index, &l2_table); if (ret < 0) { return ret; } + + /* Then decrease the refcount of the old table */ + if (l2_offset) { + qcow2_free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t)); + } l2_offset = s->l1_table[l1_index] & ~QCOW_OFLAG_COPIED; } |