cache: warn if caching causes troubles

Certain stacks of cached LVs may have unexpected consequences.
So add a warning function called when LV is cached to detect
such caces and WARN user about them - the best we could do ATM.

WHATS_NEW

@@ -1,5 +1,6 @@
 Version 2.02.131 - 
 =====================================
+  Warn user when caching raid or thin pool data LV.
   When layering LV, move LV flags with segments.
   Ignore persistent cache if configuration changed. (2.02.127)
   Fix devices/filter to be applied before disk-accessing filters. (2.02.112)

lib/metadata/cache_manip.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2014 Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2014-2015 Red Hat, Inc. All rights reserved.
  *
  * This file is part of LVM2.
  *
@@ -101,6 +101,23 @@ int cache_set_mode(struct lv_segment *seg, const char *str)
 	return 1;
 }
 
+/*
+ * At least warn a user if certain cache stacks may present some problems
+ */
+void cache_check_for_warns(const struct lv_segment *seg)
+{
+	struct logical_volume *origin_lv = seg_lv(seg, 0);
+
+	if (lv_is_raid(origin_lv) &&
+	    first_seg(seg->pool_lv)->feature_flags & DM_CACHE_FEATURE_WRITEBACK)
+		log_warn("WARNING: Data redundancy is lost with writeback "
+			 "caching of raid logical volume!");
+
+	if (lv_is_thin_pool_data(seg->lv))
+		log_warn("WARNING: Cached thin pool's data cannot be currently "
+			 "resized and require manual uncache before resize!");
+}
+
 int update_cache_pool_params(const struct segment_type *segtype,
 			     struct volume_group *vg, unsigned attr,
 			     int passed_args, uint32_t pool_data_extents,

lib/metadata/lv_manip.c

@@ -7516,6 +7516,8 @@ static struct logical_volume *_lv_create_an_lv(struct volume_group *vg,
 		if (!cache_set_policy(first_seg(lv), lp->policy_name, lp->policy_settings))
 			return_NULL; /* revert? */
 
+		cache_check_for_warns(first_seg(lv));
+
 		if (!lv_update_and_reload(lv)) {
 			/* FIXME Do a better revert */
 			log_error("Aborting. Manual intervention required.");

lib/metadata/metadata-exported.h

@@ -1158,6 +1158,7 @@ int cache_mode_is_set(const struct lv_segment *seg);
 int cache_set_mode(struct lv_segment *cache_seg, const char *str);
 int cache_set_policy(struct lv_segment *cache_seg, const char *name,
 		     const struct dm_config_tree *settings);
+void cache_check_for_warns(const struct lv_segment *seg);
 int update_cache_pool_params(const struct segment_type *segtype,
 			     struct volume_group *vg, unsigned attr,
 			     int passed_args, uint32_t pool_data_extents,

test/shell/lvconvert-cache-raid.sh

@@ -24,7 +24,7 @@ aux prepare_vg 5 80
 
 # Bug 1095843
 # lvcreate RAID1 origin, lvcreate cache-pool, and lvconvert to cache
-lvcreate --type raid1 -m 1 -l 2 -n $lv1 $vg
+lvcreate --type raid1 -m 1 --nosync -l 2 -n $lv1 $vg
 lvcreate --type cache-pool -l 1 -n ${lv1}_cachepool $vg
 lvconvert --cache --cachepool $vg/${lv1}_cachepool $vg/$lv1
 check lv_exists $vg/${lv1}_corig_rimage_0 # ensure images are properly renamed
@@ -33,17 +33,19 @@ lvremove -f $vg
 
 
 # lvcreate RAID1 origin, lvcreate RAID1 cache-pool, and lvconvert to cache
-lvcreate --type raid1 -m 1 -l 2 -n $lv1 $vg
+lvcreate --type raid1 -m 1 --nosync -l 2 -n $lv1 $vg
-lvcreate --type raid1 -m 1 -l 2 -n ${lv1}_cachepool $vg
+lvcreate --type raid1 -m 1 --nosync -l 2 -n ${lv1}_cachepool $vg
 #should lvs -a $vg/${lv1}_cdata_rimage_0  # ensure images are properly renamed
-lvconvert --yes --type cache --cachepool $vg/${lv1}_cachepool $vg/$lv1
+lvconvert --yes --type cache --cachemode writeback --cachepool $vg/${lv1}_cachepool $vg/$lv1 2>&1 | tee out
+grep "WARNING: Data redundancy is lost" out
 check lv_exists $vg/${lv1}_corig_rimage_0        # ensure images are properly renamed
 dmsetup table ${vg}-$lv1 | grep cache   # ensure it is loaded in kernel
 lvremove -f $vg
 
 
-lvcreate -n corigin -m 1 --type raid1 -l 10 $vg
+lvcreate -n corigin -m 1 --type raid1 --nosync -l 10 $vg
-lvcreate -n cpool --type cache $vg/corigin -l 10
+lvcreate -n cpool --type cache $vg/corigin --cachemode writeback -l 10 2>&1 | tee out
+grep "WARNING: Data redundancy is lost" out
 lvconvert --splitmirrors 1 --name split $vg/corigin "$dev1"
 
 lvremove -f $vg

tools/lvconvert.c

@@ -3191,6 +3191,8 @@ static int _lvconvert_cache(struct cmd_context *cmd,
 	if (!cache_set_policy(first_seg(cache_lv), lp->policy_name, lp->policy_settings))
 		return_0;
 
+	cache_check_for_warns(first_seg(cache_lv));
+
 	if (!lv_update_and_reload(cache_lv))
 		return_0;