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qcow2: Make qcow2_alloc_bytes() more explicit

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In case of -EAGAIN returned by update_refcount(), we should discard the
cluster offset we were trying to allocate and request a new one, because
in theory that old offset might now be taken by a refcount block.

In practice, this was not the case due to update_refcount() generally
returning strictly monotonic increasing cluster offsets. However, this
behavior is not set in stone, and it is also not obvious when looking at
qcow2_alloc_bytes() alone, so we should not rely on it.

Reported-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Max Reitz 2015-09-11 18:47:51 +02:00 committed by Kevin Wolf
parent 3efffc3292
commit 2ac01520be
1 changed files with 6 additions and 0 deletions
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6
block/qcow2-refcount.c
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@ -949,11 +949,17 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size)
if (!offset || ROUND_UP(offset, s->cluster_size) != new_cluster) {
offset = new_cluster;
free_in_cluster = s->cluster_size;
} else {
free_in_cluster += s->cluster_size;
}
}
assert(offset);
ret = update_refcount(bs, offset, size, 1, false, QCOW2_DISCARD_NEVER);
if (ret < 0) {
offset = 0;
}
} while (ret == -EAGAIN);
if (ret < 0) {
return ret;