Commit 16fde5f2 authored by Kevin Wolf's avatar Kevin Wolf
Browse files

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: default avatarKevin Wolf <kwolf@redhat.com>
parent a9ae2bff

block/qcow2-cluster.c

+6 −3
Original line number Diff line number Diff line
@@ -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;

    }