Allow snapshots in a cluster as long as they are exclusively

activated.

In order to achieve this, we need to be able to query whether
the origin is active exclusively (a condition of being able to
add an exclusive snapshot).

Once we are able to query the exclusive activation of an LV, we
can safely create/activate the snapshot.

A change to 'hold_lock' was also made so that a request to aquire
a WRITE lock did not replace an EX lock, which is already a form
of write lock.

9 files changed, 122 insertions, 31 deletions

diff --git a/WHATS_NEW b/WHATS_NEW
index 54f05f06..a43433f0 100644
--- a/WHATS_NEW
+++ b/WHATS_NEW
@@ -1,5 +1,6 @@
 Version 2.02.83 - 
 ===================================
+  Allow exclusive activation of snapshots in a cluster.
   Add --addnodeonresume, --addnodeoncreate options for dmsetup create.
   Use cluster-wide message to request device name sync.
   Fix operation node stacking for consecutive dm ops.
diff --git a/daemons/clvmd/lvm-functions.c b/daemons/clvmd/lvm-functions.c
index 1fa23483..81e8b884 100644
--- a/daemons/clvmd/lvm-functions.c
+++ b/daemons/clvmd/lvm-functions.c
@@ -240,9 +240,17 @@ static int hold_lock(char *resource, int mode, int flags)
 
 	lvi = lookup_info(resource);
 
-	if (lvi && lvi->lock_mode == mode) {
-		DEBUGLOG("hold_lock, lock mode %d already held\n", mode);
-		return 0;
+	if (lvi) {
+		if (lvi->lock_mode == mode) {
+			DEBUGLOG("hold_lock, lock mode %d already held\n",
+				 mode);
+			return 0;
+		}
+		if ((lvi->lock_mode == LCK_EXCL) && (mode == LCK_WRITE)) {
+			DEBUGLOG("hold_lock, lock already held LCK_EXCL, "
+				 "ignoring LCK_WRITE request");
+			return 0;
+		}
 	}
 
 	/* Only allow explicit conversions */
diff --git a/lib/activate/activate.c b/lib/activate/activate.c
index d8f31bab..9edb0114 100644
--- a/lib/activate/activate.c
+++ b/lib/activate/activate.c
@@ -708,39 +708,108 @@ int lvs_in_vg_opened(const struct volume_group *vg)
 }
 
 /*
+ * _lv_is_active
+ * @lv:        logical volume being queried
+ * @locally:   set if active locally (when provided)
+ * @exclusive: set if active exclusively (when provided)
+ *
  * Determine whether an LV is active locally or in a cluster.
- * Assumes vg lock held.
- * Returns:
- * 0 - not active locally or on any node in cluster
- * 1 - active either locally or some node in the cluster
+ * In addition to the return code which indicates whether or
+ * not the LV is active somewhere, two other values are set
+ * to yield more information about the status of the activation:
+ *	return	locally	exclusively	status
+ *	======	=======	===========	======
+ *	   0	   0	    0		not active
+ *	   1	   0	    0		active remotely
+ *	   1	   0	    1		exclusive remotely
+ *	   1	   1	    0		active locally and possibly remotely
+ *	   1	   1	    1		exclusive locally (or local && !cluster)
+ * The VG lock must be held to call this function.
+ *
+ * Returns: 0 or 1
  */
-int lv_is_active(struct logical_volume *lv)
+static int _lv_is_active(struct logical_volume *lv,
+			 int *locally, int *exclusive)
 {
-	int ret;
+	int r, l, e; /* remote, local, and exclusive */
+
+	r = l = e = 0;
 
 	if (_lv_active(lv->vg->cmd, lv))
-		return 1;
+		l = 1;
 
-	if (!vg_is_clustered(lv->vg))
-		return 0;
+	if (!vg_is_clustered(lv->vg)) {
+		e = 1;  /* exclusive by definition */
+		goto out;
+	}
+
+	/* Active locally, and the caller doesn't care about exclusive */
+	if (l && !exclusive)
+		goto out;
 
-	if ((ret = remote_lock_held(lv->lvid.s)) >= 0)
-		return ret;
+	if ((r = remote_lock_held(lv->lvid.s, &e)) >= 0)
+		goto out;
 
 	/*
-	 * Old compatibility code if locking doesn't support lock query
-	 * FIXME: check status to not deactivate already activate device
+	 * If lock query is not supported (due to interfacing with old
+	 * code), then we cannot evaluate exclusivity properly.
+	 *
+	 * Old users of this function will never be affected by this,
+	 * since they are only concerned about active vs. not active.
+	 * New users of this function who specifically ask for 'exclusive'
+	 * will be given an error message.
 	 */
+	if (l) {
+		if (exclusive)
+			log_error("Unable to determine exclusivity of %s",
+				  lv->name);
+		goto out;
+	}
+
 	if (activate_lv_excl(lv->vg->cmd, lv)) {
 		if (!deactivate_lv(lv->vg->cmd, lv))
 			stack;
 		return 0;
 	}
 
-	/*
-	 * Exclusive local activation failed so assume it is active elsewhere.
-	 */
-	return 1;
+out:
+	if (locally)
+		*locally = l;
+	if (exclusive)
+		*exclusive = e;
+
+	log_very_verbose("%s/%s is %sactive%s%s",
+			 lv->vg->name, lv->name,
+			 (r || l) ? "" : "not ",
+			 (exclusive && e) ? " exclusive" : "",
+			 e ? (l ? " locally" : " remotely") : "");
+
+	return r || l;
+}
+
+int lv_is_active(struct logical_volume *lv)
+{
+	return _lv_is_active(lv, NULL, NULL);
+}
+
+/*
+int lv_is_active_locally(struct logical_volume *lv)
+{
+	int l;
+	return _lv_is_active(lv, &l, NULL) && l;
+}
+*/
+
+int lv_is_active_exclusive_locally(struct logical_volume *lv)
+{
+	int l, e;
+	return _lv_is_active(lv, &l, &e) && l && e;
+}
+
+int lv_is_active_exclusive_remotely(struct logical_volume *lv)
+{
+	int l, e;
+	return _lv_is_active(lv, &l, &e) && !l && e;
 }
 
 #ifdef DMEVENTD
diff --git a/lib/activate/activate.h b/lib/activate/activate.h
index 2bc73dd8..c054c6db 100644
--- a/lib/activate/activate.h
+++ b/lib/activate/activate.h
@@ -94,6 +94,8 @@ int lvs_in_vg_activated(struct volume_group *vg);
 int lvs_in_vg_opened(const struct volume_group *vg);
 
 int lv_is_active(struct logical_volume *lv);
+int lv_is_active_exclusive_locally(struct logical_volume *lv);
+int lv_is_active_exclusive_remotely(struct logical_volume *lv);
 
 int lv_has_target_type(struct dm_pool *mem, struct logical_volume *lv,
 		       const char *layer, const char *target_type);
diff --git a/lib/activate/dev_manager.c b/lib/activate/dev_manager.c
index 1fbefc4e..b4854048 100644
--- a/lib/activate/dev_manager.c
+++ b/lib/activate/dev_manager.c
@@ -1390,10 +1390,6 @@ static int _add_segment_to_dtree(struct dev_manager *dm,
 	/* 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"))
diff --git a/lib/locking/locking.c b/lib/locking/locking.c
index 645f25d5..520b25ee 100644
--- a/lib/locking/locking.c
+++ b/lib/locking/locking.c
@@ -545,7 +545,7 @@ 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;
 
@@ -563,5 +563,8 @@ int remote_lock_held(const char *vol)
 		return 1;
 	}
 
+	if (exclusive)
+		*exclusive = (mode == LCK_EXCL);
+
 	return mode == LCK_NULL ? 0 : 1;
 }
diff --git a/lib/locking/locking.h b/lib/locking/locking.h
index 51a7198c..f30a76ce 100644
--- a/lib/locking/locking.h
+++ b/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:
diff --git a/lib/metadata/lv_manip.c b/lib/metadata/lv_manip.c
index f6bb68c2..eb2a3e4a 100644
--- a/lib/metadata/lv_manip.c
+++ b/lib/metadata/lv_manip.c
@@ -3164,11 +3164,6 @@ int lv_create_single(struct volume_group *vg,
 				  "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 +3212,13 @@ int lv_create_single(struct volume_group *vg,
 				return 0;
 			}
 			origin_active = info.exists;
+
+			if (vg_is_clustered(vg) &&
+			    !lv_is_active_exclusive_locally(org)) {
+				log_error("%s must be active exclusively to"
+					  " create snapshot", org->name);
+				return 0;
+			}
 		}
 	}
 
diff --git a/tools/vgchange.c b/tools/vgchange.c
index f2d399c4..4266d633 100644
--- a/tools/vgchange.c
+++ b/tools/vgchange.c
@@ -115,6 +115,16 @@ static int _activate_lvs_in_vg(struct cmd_context *cmd,
 		    ((lv->status & PVMOVE) ))
 			continue;
 
+		/*
+		 * If the LV is active exclusive remotely,
+		 * then ignore it here
+		 */
+		if (lv_is_active_exclusive_remotely(lv)) {
+			log_verbose("%s/%s is exclusively active on"
+				    " a remote node", vg->name, lv->name);
+			continue;
+		}
+
 		expected_count++;
 
 		if (activate == CHANGE_AN) {