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qcow2: Fix order in L2 table COW

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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>
This commit is contained in:
Kevin Wolf 2011-02-09 17:36:19 +01:00
parent a9ae2bffea
commit 16fde5f2c2
1 changed files with 6 additions and 3 deletions
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9
block/qcow2-cluster.c
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@ -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;
}