Make pointer that points from the origin to the segment that represents
merging snapshot.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 lib/metadata/lv_manip.c          |    1 +
 lib/metadata/metadata-exported.h |    3 +++
 lib/metadata/snapshot_manip.c    |   10 +++++++++-
 tools/lvconvert.c                |   11 +++++++++--
 4 files changed, 22 insertions(+), 3 deletions(-)

Index: LVM2.2.02.39/lib/metadata/lv_manip.c
===================================================================
--- LVM2.2.02.39.orig/lib/metadata/lv_manip.c	2008-07-06 16:35:50.000000000 +0200
+++ LVM2.2.02.39/lib/metadata/lv_manip.c	2008-07-06 16:38:23.000000000 +0200
@@ -1795,6 +1795,7 @@ char *generate_lv_name(struct volume_gro
 void lv_init(struct logical_volume *lv)
 {
 	lv->snapshot = NULL;
+	lv->merging_snapshot = NULL;
 	list_init(&lv->snapshot_segs);
 	list_init(&lv->segments);
 	list_init(&lv->tags);
Index: LVM2.2.02.39/lib/metadata/metadata-exported.h
===================================================================
--- LVM2.2.02.39.orig/lib/metadata/metadata-exported.h	2008-07-06 16:35:31.000000000 +0200
+++ LVM2.2.02.39/lib/metadata/metadata-exported.h	2008-07-06 16:37:04.000000000 +0200
@@ -292,6 +292,9 @@ struct logical_volume {
 	struct list snapshot_segs;
 	struct lv_segment *snapshot;
 
+	/* A snapshot that is merging into this origin */
+	struct lv_segment *merging_snapshot;
+
 	struct list segments;
 	struct list tags;
 	struct list segs_using_this_lv;
Index: LVM2.2.02.39/lib/metadata/snapshot_manip.c
===================================================================
--- LVM2.2.02.39.orig/lib/metadata/snapshot_manip.c	2008-07-06 16:35:42.000000000 +0200
+++ LVM2.2.02.39/lib/metadata/snapshot_manip.c	2008-07-06 16:38:02.000000000 +0200
@@ -68,6 +68,11 @@ int vg_add_snapshot(const char *name, st
 		return 0;
 	}
 
+	if (cow->status & SNAPSHOT_MERGE && origin->merging_snapshot) {
+		log_error("Origin has already merging snapshot.");
+		return 0;
+	}
+
 	if (!(snap = lv_create_empty(name ? name : "snapshot%d",
 				     lvid, LVM_READ | LVM_WRITE | VISIBLE_LV,
 				     ALLOC_INHERIT, 1, origin->vg)))
@@ -82,7 +87,10 @@ int vg_add_snapshot(const char *name, st
 	seg->origin = origin;
 	seg->cow = cow;
 	seg->lv->status |= SNAPSHOT;
-	if (merge) seg->status |= SNAPSHOT_MERGE;
+	if (merge) {
+		seg->status |= SNAPSHOT_MERGE;
+		origin->merging_snapshot = seg;
+	}
 
 	origin->origin_count++;
 	origin->vg->snapshot_count++;
Index: LVM2.2.02.39/tools/lvconvert.c
===================================================================
--- LVM2.2.02.39.orig/tools/lvconvert.c	2008-07-06 16:35:56.000000000 +0200
+++ LVM2.2.02.39/tools/lvconvert.c	2008-07-06 17:24:20.000000000 +0200
@@ -708,12 +708,19 @@ static int lvconvert_merge(struct cmd_co
 			   struct lvconvert_params *lp)
 {
 	struct logical_volume *origin = origin_from_cow(lv);
+	struct lv_segment *cow_seg = find_cow(lv);
 
-	if (find_cow(lv)->status & SNAPSHOT_MERGE) {
+	if (cow_seg->status & SNAPSHOT_MERGE) {
 		log_error("Snapshot %s is already merging", lv->name);
 		return 0;
 	}
-	find_cow(lv)->status |= SNAPSHOT_MERGE;
+	if (origin->merging_snapshot) {
+		log_error("Another snapshot is already merging");
+		return 0;
+	}
+
+	cow_seg->status |= SNAPSHOT_MERGE;
+	origin->merging_snapshot = cow_seg;
 
 	/* store vg on disk(s) */
 	if (!vg_write(lv->vg))