LVM: allow exclusive snapshots in cluster

Index: LVM2/lib/activate/activate.c
===================================================================
@@ -701,20 +701,22 @@ int lvs_in_vg_opened(const struct volume
  * Returns:
  * 0 - not active locally or on any node in cluster
  * 1 - active either locally or some node in the cluster
+ * 2 - active exclusively on this node
  */
 int lv_is_active(struct logical_volume *lv)
 {
-	int ret;
+	int r;
+	int ret = 0;
 
 	if (_lv_active(lv->vg->cmd, lv))
-		return 1;
+		ret++;
 
 	if (!vg_is_clustered(lv->vg))
-		return 0;
-
-	if ((ret = remote_lock_held(lv->lvid.s)) >= 0)
 		return ret;
 
+	if ((r = remote_lock_held(lv->lvid.s, ret)) >= 0)
+		return ret + r;
+
 	/*
 	 * Old compatibility code if locking doesn't support lock query
 	 * FIXME: check status to not deactivate already activate device

Index: LVM2/lib/activate/dev_manager.c
===================================================================
@@ -1390,10 +1390,6 @@ static int _add_segment_to_dtree(struct 
 	/* If this is a snapshot origin, add real LV */
 	/* If this is a snapshot origin + merging snapshot, add cow + real LV */
 	} else if (lv_is_origin(seg->lv) && !layer) {
-		if (vg_is_clustered(seg->lv->vg)) {
-			log_error("Clustered snapshots are not yet supported");
-			return 0;
-		}
 		if (lv_is_merging_origin(seg->lv)) {
 			if (!_add_new_lv_to_dtree(dm, dtree,
 			     find_merging_cow(seg->lv)->cow, "cow"))

Index: LVM2/lib/locking/locking.c
===================================================================
@@ -545,9 +545,9 @@ int locking_is_clustered(void)
 	return (_locking.flags & LCK_CLUSTERED) ? 1 : 0;
 }
 
-int remote_lock_held(const char *vol)
+int remote_lock_held(const char *vol, int exclusive)
 {
-	int mode = LCK_NULL;
+	int m;
 
 	if (!locking_is_clustered())
 		return 0;

@@ -558,10 +558,13 @@ int remote_lock_held(const char *vol)
 	/*
 	 * If an error occured, expect that volume is active
 	 */
-	if (!_locking.query_resource(vol, &mode)) {
+	if (!_locking.query_resource(vol, &m)) {
 		stack;
 		return 1;
 	}
 
-	return mode == LCK_NULL ? 0 : 1;
+	if (exclusive)
+		return m == LCK_EXCL;
+
+	return m == LCK_NULL ? 0 : 1;
 }

Index: LVM2/lib/locking/locking.h
===================================================================
@@ -25,7 +25,7 @@ void reset_locking(void);
 int vg_write_lock_held(void);
 int locking_is_clustered(void);
 
-int remote_lock_held(const char *vol);
+int remote_lock_held(const char *vol, int exclusive);
 
 /*
  * LCK_VG:

Index: LVM2/lib/metadata/lv_manip.c
===================================================================
@@ -3164,11 +3164,6 @@ int lv_create_single(struct volume_group
 				  "device-mapper kernel driver");
 			return 0;
 		}
-		/* FIXME Allow exclusive activation. */
-		if (vg_is_clustered(vg)) {
-			log_error("Clustered snapshots are not yet supported.");
-			return 0;
-		}
 
 		/* Must zero cow */
 		status |= LVM_WRITE;

@@ -3217,6 +3212,12 @@ int lv_create_single(struct volume_group
 				return 0;
 			}
 			origin_active = info.exists;
+
+			if (vg_is_clustered(vg) && (lv_is_active(org) != 2)) {
+				log_error("%s must be active exclusively to"
+					  " create snapshot", org->name);
+				return 0;
+			}
 		}
 	}