snapshot: expose new delete flag in virsh

It would technically be possible to have virsh compute the list
of descendants of a given snapshot, then delete those one at
a time.  But it's complex, and not worth writing for a first
cut at implementing the new flags.

* tools/virsh.c (cmdSnapshotDelete): Add --children-only,
--metadata.
* tools/virsh.pod (snapshot-delete): Document them.

tools/virsh.c

@@ -12769,6 +12769,9 @@ static const vshCmdOptDef opts_snapshot_delete[] = {
     {"domain", VSH_OT_DATA, VSH_OFLAG_REQ, N_("domain name, id or uuid")},
     {"snapshotname", VSH_OT_DATA, VSH_OFLAG_REQ, N_("snapshot name")},
     {"children", VSH_OT_BOOL, 0, N_("delete snapshot and all children")},
+    {"children-only", VSH_OT_BOOL, 0, N_("delete children but not snapshot")},
+    {"metadata", VSH_OT_BOOL, 0,
+     N_("delete only libvirt metadata, leaving snapshot contents behind")},
     {NULL, 0, 0, NULL}
 };
 
@@ -12793,12 +12796,22 @@ cmdSnapshotDelete(vshControl *ctl, const vshCmd *cmd)
 
     if (vshCommandOptBool(cmd, "children"))
         flags |= VIR_DOMAIN_SNAPSHOT_DELETE_CHILDREN;
+    if (vshCommandOptBool(cmd, "children-only"))
+        flags |= VIR_DOMAIN_SNAPSHOT_DELETE_CHILDREN_ONLY;
+    if (vshCommandOptBool(cmd, "metadata"))
+        flags |= VIR_DOMAIN_SNAPSHOT_DELETE_METADATA_ONLY;
 
     snapshot = virDomainSnapshotLookupByName(dom, name, 0);
     if (snapshot == NULL)
         goto cleanup;
 
+    /* XXX If we wanted, we could emulate DELETE_CHILDREN_ONLY even on
+     * older servers that reject the flag, by manually computing the
+     * list of descendants.  But that's a lot of code to maintain.  */
     if (virDomainSnapshotDelete(snapshot, flags) == 0) {
+        if (flags & VIR_DOMAIN_SNAPSHOT_DELETE_CHILDREN_ONLY)
+            vshPrint(ctl, _("Domain snapshot %s children deleted\n"), name);
+        else
             vshPrint(ctl, _("Domain snapshot %s deleted\n"), name);
     } else {
         vshError(ctl, _("Failed to delete snapshot %s"), name);

tools/virsh.pod

@@ -1815,12 +1815,20 @@ I<--running> or I<--paused> flag will perform additional state changes
 transient domains cannot be inactive, it is required to use one of these
 flags when reverting to a disk snapshot of a transient domain.
 
-=item B<snapshot-delete> I<domain> I<snapshot> I<--children>
+=item B<snapshot-delete> I<domain> I<snapshot> [I<--metadata>]
+[{I<--children> | I<--children-only>}]
 
 Delete the snapshot for the domain named I<snapshot>.  If this snapshot
 has child snapshots, changes from this snapshot will be merged into the
 children.  If I<--children> is passed, then delete this snapshot and any
-children of this snapshot.
+children of this snapshot.  If I<--children-only> is passed, then delete
+any children of this snapshot, but leave this snapshot intact.  These
+two flags are mutually exclusive.
+
+If I<--metadata> is specified, then only delete the snapshot metadata
+maintained by libvirt, while leaving the snapshot contents intact for
+access by external tools; otherwise deleting a snapshot also removes
+the data contents from that point in time.
 
 =back