Allow dm-cache cache device to be standard LV

If a single, standard LV is specified as the cache, use
it directly instead of converting it into a cache-pool
object with two separate LVs (for data and metadata).

With a single LV as the cache, lvm will use blocks at the
beginning for metadata, and the rest for data.  Separate
dm linear devices are set up to point at the metadata and
data areas of the LV.  These dm devs are given to the
dm-cache target to use.

The single LV cache cannot be resized without recreating it.

If the --poolmetadata option is used to specify an LV for
metadata, then a cache pool will be created (with separate
LVs for data and metadata.)

Usage:

$ lvcreate -n main -L 128M vg /dev/loop0

$ lvcreate -n fast -L 64M vg /dev/loop1

$ lvs -a vg
  LV   VG Attr       LSize   Type   Devices
  main vg -wi-a----- 128.00m linear /dev/loop0(0)
  fast vg -wi-a-----  64.00m linear /dev/loop1(0)

$ lvconvert --type cache --cachepool fast vg/main

$ lvs -a vg
  LV           VG Attr       LSize   Origin       Pool  Type   Devices
  [fast]       vg Cwi---C---  64.00m                     linear /dev/loop1(0)
  main         vg Cwi---C--- 128.00m [main_corig] [fast] cache  main_corig(0)
  [main_corig] vg owi---C--- 128.00m                     linear /dev/loop0(0)

$ lvchange -ay vg/main

$ dmsetup ls
vg-fast_cdata   (253:4)
vg-fast_cmeta   (253:5)
vg-main_corig   (253:6)
vg-main (253:24)
vg-fast (253:3)

$ dmsetup table
vg-fast_cdata: 0 98304 linear 253:3 32768
vg-fast_cmeta: 0 32768 linear 253:3 0
vg-main_corig: 0 262144 linear 7:0 2048
vg-main: 0 262144 cache 253:5 253:4 253:6 128 2 metadata2 writethrough mq 0
vg-fast: 0 131072 linear 7:1 2048

$ lvchange -an vg/min

$ lvconvert --splitcache vg/main

$ lvs -a vg
  LV   VG Attr       LSize   Type   Devices
  fast vg -wi-------  64.00m linear /dev/loop1(0)
  main vg -wi------- 128.00m linear /dev/loop0(0)

1 files changed, 17 insertions, 3 deletions

diff --git a/lib/report/report.c b/lib/report/report.c
index 52baa6cbb..ecec0a320 100644
--- a/lib/report/report.c
+++ b/lib/report/report.c
@@ -1430,7 +1430,10 @@ static int _cache_settings_disp(struct dm_report *rh, struct dm_pool *mem,
 	struct _str_list_append_baton baton;
 	struct dm_list dummy_list; /* dummy list to display "nothing" */
 
-	if (seg_is_cache_pool(seg))
+	if (seg_is_cache(seg) && lv_is_cache_single(seg->pool_lv))
+		setting_seg = seg;
+
+	else if (seg_is_cache_pool(seg))
 		setting_seg = seg;
 
 	else if (seg_is_cache(seg))
@@ -1565,7 +1568,10 @@ static int _cache_policy_disp(struct dm_report *rh, struct dm_pool *mem,
 	const struct lv_segment *seg = (const struct lv_segment *) data;
 	const struct lv_segment *setting_seg = NULL;
 
-	if (seg_is_cache_pool(seg))
+	if (seg_is_cache(seg) && lv_is_cache_single(seg->pool_lv))
+		setting_seg = seg;
+
+	else if (seg_is_cache_pool(seg))
 		setting_seg = seg;
 
 	else if (seg_is_cache(seg))
@@ -2747,7 +2753,10 @@ static int _cachemetadataformat_disp(struct dm_report *rh, struct dm_pool *mem,
 	const struct lv_segment *setting_seg = NULL;
 	const uint64_t *fmt;
 
-	if (seg_is_cache_pool(seg))
+	if (seg_is_cache(seg) && lv_is_cache_single(seg->pool_lv))
+		setting_seg = seg;
+
+	else if (seg_is_cache_pool(seg))
 		setting_seg = seg;
 
 	else if (seg_is_cache(seg))
@@ -3222,6 +3231,11 @@ static int _lvmetadatasize_disp(struct dm_report *rh, struct dm_pool *mem,
 	const struct logical_volume *lv = (const struct logical_volume *) data;
 	uint64_t size;
 
+	if (lv_is_cache(lv) && lv_is_cache_single(first_seg(lv)->pool_lv)) {
+		size = lv_metadata_size(lv);
+		return _size64_disp(rh, mem, field, &size, private);
+	}
+
 	if (lv_is_thin_pool(lv) || lv_is_cache_pool(lv)) {
 		size = lv_metadata_size(lv);
 		return _size64_disp(rh, mem, field, &size, private);