qcow2: Invalidate cache after failed read

The cache content may be destroyed after a failed read, better not use it any
more.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

block/qcow2-cluster.c

@@ -188,6 +188,7 @@ static int l2_load(BlockDriverState *bs, uint64_t l2_offset,
     ret = bdrv_pread(bs->file, l2_offset, *l2_table,
         s->l2_size * sizeof(uint64_t));
     if (ret < 0) {
+        qcow2_l2_cache_reset(bs);
         return ret;
     }
 

block/qcow2-refcount.c

@@ -103,6 +103,7 @@ static int load_refcount_block(BlockDriverState *bs,
     ret = bdrv_pread(bs->file, refcount_block_offset, s->refcount_block_cache,
                      s->cluster_size);
     if (ret < 0) {
+        s->refcount_block_cache_offset = 0;
         return ret;
     }