Convey need for snapshot-merge target in lvconvert error message and man

page.

Add ->target_name to segtype_handler to allow a more specific target
name to be returned based on the state of the segment.

Result of trying to merge a snapshot using a kernel that doesn't have
the snapshot-merge target:

Before:
# lvconvert --merge vg/snap
  Can't expand LV lv: snapshot target support missing from kernel?
  Failed to suspend origin lv

After:
# lvconvert --merge vg/snap
  Can't process LV lv: snapshot-merge target support missing from kernel?
  Failed to suspend origin lv
  Unable to merge LV "snap" into it's origin.

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/snapshot/snapshot.c b/lib/snapshot/snapshot.c
index 92f89111..30e78d47 100644
--- a/lib/snapshot/snapshot.c
+++ b/lib/snapshot/snapshot.c
@@ -28,6 +28,14 @@ static const char *_snap_name(const struct lv_segment *seg)
 	return seg->segtype->name;
 }
 
+static const char *_snap_target_name(const struct lv_segment *seg)
+{
+	if (seg->status & MERGING)
+		return "snapshot-merge";
+
+	return _snap_name(seg);
+}
+
 static int _snap_text_import(struct lv_segment *seg, const struct config_node *sn,
 			struct dm_hash_table *pv_hash __attribute__((unused)))
 {
@@ -217,6 +225,7 @@ static void _snap_destroy(const struct segment_type *segtype)
 
 static struct segtype_handler _snapshot_ops = {
 	.name = _snap_name,
+	.target_name = _snap_target_name,
 	.text_import = _snap_text_import,
 	.text_export = _snap_text_export,
 	.target_status_compatible = _snap_target_status_compatible,