rbd:snap limit should't be set smaller than the num of existing snaps

new snap limit must be bigger than the num of existing snaps

Signed-off-by: PCzhangPC <pengcheng.zhang@easystack.cn>

src/cls/rbd/cls_rbd.cc

@@ -2807,7 +2807,29 @@ int snapshot_set_limit(cls_method_context_t hctx, bufferlist *in,
     return -EINVAL;
   }
 
-  if (new_limit == UINT64_MAX) {
+  int max_read = RBD_MAX_KEYS_READ;
+  size_t snap_count = 0;
+  string last_read = RBD_SNAP_KEY_PREFIX;
+  bool more;
+
+  do {
+    set<string> keys;
+    rc = cls_cxx_map_get_keys(hctx, last_read, max_read, &keys, &more);
+    if (rc < 0)
+      return rc;
+    for (auto& key : keys) {
+      if (key.find(RBD_SNAP_KEY_PREFIX) != 0)
+        break;
+      snap_count++;
+    }
+    if (!keys.empty())
+      last_read = *(keys.rbegin());
+  } while (more);
+
+  if (new_limit < snap_count){
+    CLS_ERR("error setting snapshot limit: %s", cpp_strerror(rc).c_str());
+    return -ERANGE;
+  } else if (new_limit == UINT64_MAX) {
     CLS_LOG(20, "remove snapshot limit\n");
     rc = cls_cxx_map_remove_key(hctx, "snap_limit");
   } else {
@@ -5305,7 +5327,7 @@ CLS_INIT(rbd)
 			  CLS_METHOD_RD,
 			  snapshot_get_limit, &h_snapshot_get_limit);
   cls_register_cxx_method(h_class, "snapshot_set_limit",
-			  CLS_METHOD_WR,
+			  CLS_METHOD_RD | CLS_METHOD_WR,
 			  snapshot_set_limit, &h_snapshot_set_limit);
 
   /* methods for the rbd_children object */

src/librbd/journal/Replay.cc

@@ -772,6 +772,8 @@ void Replay<I>::handle_event(const journal::SnapLimitEvent &event,
 							   event,
 							   on_op_complete));
 
+  op_event->ignore_error_codes = {-ERANGE};
+
   on_ready->complete(0);
 }