crush: fix potential class id collision

Signed-off-by: xie xingguo <xie.xingguo@zte.com.cn>

src/crush/CrushWrapper.cc

@@ -1283,6 +1283,31 @@ int CrushWrapper::trim_roots_with_class(bool unused)
   return 0;
 }
 
+int32_t CrushWrapper::_alloc_class_id() const {
+  if (class_name.empty()) {
+    return 0;
+  }
+  int32_t class_id = class_name.rbegin()->first + 1;
+  if (class_id >= 0) {
+    return class_id;
+  }
+  // wrapped, pick a random start and do exhaustive search
+  uint32_t upperlimit = numeric_limits<int32_t>::max() + 1;
+  class_id = rand() % upperlimit;
+  const auto start = class_id;
+  do {
+    if (!class_name.count(class_id)) {
+      return class_id;
+    } else {
+      class_id++;
+      if (class_id < 0) {
+        class_id = 0;
+      }
+    }
+  } while (class_id != start);
+  assert(0 == "no available class id");
+}
+
 void CrushWrapper::reweight(CephContext *cct)
 {
   set<int> roots;

src/crush/CrushWrapper.h

@@ -482,10 +482,12 @@ public:
     return 0;
   }
 
+  int32_t _alloc_class_id() const;
+
   int get_or_create_class_id(const string& name) {
     int c = get_class_id(name);
     if (c < 0) {
-      int i = class_name.size();
+      int i = _alloc_class_id();
       class_name[i] = name;
       class_rname[name] = i;
       return i;