mds/SimpleLock: add has_xlock_by()

This replaces get_xlock_by() in cases where only a not-nullptr check
is needed; this eliminates costly implicit reference counter
manipulations.

Signed-off-by: Max Kellermann <[email protected]>

Author: MaxKellermann

src/mds/LocalLockC.h

@@ -30,7 +30,7 @@ class LocalLockC : public SimpleLock {
   }
 
   bool can_xlock_local() const {
-    return !is_wrlocked() && (get_xlock_by() == MutationRef());
+    return !is_wrlocked() && !has_xlock_by();
   }
 
   bool can_wrlock() const {

src/mds/SimpleLock.h

@@ -420,7 +420,7 @@ class SimpleLock {
 
   // xlock
   void get_xlock(MutationRef who, client_t client) { 
-    ceph_assert(get_xlock_by() == MutationRef());
+    ceph_assert(!has_xlock_by());
     ceph_assert(state == LOCK_XLOCK || is_locallock() ||
 	   state == LOCK_LOCK /* if we are a peer */);
     parent->get(MDSCacheObject::PIN_LOCK);
@@ -465,6 +465,9 @@ class SimpleLock {
   MutationRef get_xlock_by() const {
     return have_more() ? more()->xlock_by : MutationRef();
   }
+  bool has_xlock_by() const noexcept {
+    return have_more() && more()->xlock_by;
+  }
 
   // lease
   bool is_leased() const {