Re: [Qemu-devel] [PATCH V7 4/6] qcow2: cancel the modification on fail in qcow2_snapshot_create()

[Stefan Hajnoczi <stefanha@gmail.com>]

On Thu, Dec 05, 2013 at 08:02:50PM +0800, Wenchao Xia wrote:
> +restore_refcount:
> +    if (qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, -1)
> +        < 0 && errp) {
> +        /* Nothing can be done now, need image check later */
> +        error_setg(&err, "%s\nqcow2: Error in restoring refcount in snapshot",
> +                   error_get_pretty(*errp));
> +        error_free(*errp);
> +        *errp = NULL;
> +        error_propagate(errp, err);
> +    }

We get here if writing the new snapshot list failed.  If
qcow2_update_snapshot_refcount(..., -1) also fails I think we should
skip qcow2_free_clusters() below.  We don't know the exact state of the
disk image anymore - better to leak clusters than to have a dangling
reference.

> +dealloc_cluster:
> +    qcow2_free_clusters(bs, sn->l1_table_offset,
> +                        sn->l1_size * sizeof(uint64_t),
> +                        QCOW2_DISCARD_ALWAYS);
> +
>  fail:
>      g_free(sn->id_str);
>      g_free(sn->name);
> -- 
> 1.7.1
> 
>