Commit 2ac01520 authored Sep 11, 2015 by Max Reitz Committed by Kevin Wolf Sep 14, 2015

qcow2: Make qcow2_alloc_bytes() more explicit



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>

parent 3efffc32

block/qcow2-refcount.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -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;