migration: introduce a delete_snapshot wrapper

Make snapshot deletion consistent with the snapshot save
and load commands by using a wrapper around the blockdev
layer. The main difference is that we get upfront validation
of the passed in device list (if any).

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210204124834.774401-10-berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

include/migration/snapshot.h

@@ -48,4 +48,17 @@ bool load_snapshot(const char *name,
                    bool has_devices, strList *devices,
                    Error **errp);
 
+/**
+ * delete_snapshot: Delete a snapshot.
+ * @name: path to snapshot
+ * @has_devices: whether to use explicit device list
+ * @devices: explicit device list to snapshot
+ * @errp: pointer to error object
+ * On success, return %true.
+ * On failure, store an error through @errp and return %false.
+ */
+bool delete_snapshot(const char *name,
+                    bool has_devices, strList *devices,
+                    Error **errp);
+
 #endif

migration/savevm.c

@@ -3071,6 +3071,20 @@ err_drain:
     return false;
 }
 
+bool delete_snapshot(const char *name, bool has_devices,
+                     strList *devices, Error **errp)
+{
+    if (!bdrv_all_can_snapshot(has_devices, devices, errp)) {
+        return false;
+    }
+
+    if (bdrv_all_delete_snapshot(name, has_devices, devices, errp) < 0) {
+        return false;
+    }
+
+    return true;
+}
+
 void vmstate_register_ram(MemoryRegion *mr, DeviceState *dev)
 {
     qemu_ram_set_idstr(mr->ram_block,

monitor/hmp-cmds.c

@@ -1159,7 +1159,7 @@ void hmp_delvm(Monitor *mon, const QDict *qdict)
     Error *err = NULL;
     const char *name = qdict_get_str(qdict, "name");
 
-    bdrv_all_delete_snapshot(name, false, NULL, &err);
+    delete_snapshot(name, false, NULL, &err);
     hmp_handle_error(mon, err);
 }