new command to replace a dm-cache cachevol

This command replaces the cachevol in a cache LV
with another LV.  The replacement LV should contain
a repaired copy of the cachevol.  When the main LV
is activated, it will use the replacement cachevol
for caching.  The previous cachevol becomes a visible,
unused LV.

$ lvs -a vg
  LV           VG Attr       LSize  Pool   Origin
  [fast]       vg Cwi---C---  8.00g
  fast2        vg -wi-------  8.00g
  main         vg Cwi---C--- 32.00g [fast] [main_corig]
  [main_corig] vg owi---C--- 32.00g

$ lvconvert --replacecachevol fast mm/fast2
Replace current cachevol fast with fast2 for caching vg/main? [y/n]: y
  LV vg/main is now using cachevol vg/fast2 for caching.
  The previous cachevol vg/fast is now unused.

$ lvs -a vg
  LV           VG Attr       LSize  Pool    Origin
  fast         vg -wi-------  8.00g
  [fast2]      vg Cwi---C---  8.00g
  main         vg Cwi---C--- 32.00g [fast2] [main_corig]
  [main_corig] vg owi---C--- 32.00g

5 files changed, 175 insertions, 0 deletions

diff --git a/tools/args.h b/tools/args.h
index 16d0d9b18..c3ea96b77 100644
--- a/tools/args.h
+++ b/tools/args.h
@@ -556,6 +556,14 @@ arg(replace_ARG, '\0', "replace", pv_VAL, ARG_GROUPABLE, 0,
     "Multiple PVs can be replaced by repeating this option.\n"
     "See \\fBlvmraid\\fP(7) for more information.\n")
 
+arg(replacecachevol_ARG, '\0', "replacecachevol", lv_VAL, 0, 0,
+    "Replace the specified cachevol LV with the LV named in the\n"
+    "command's position arg. The replacement LV should hold a\n"
+    "repaired copy of the cache. The current cachevol LV will be\n"
+    "detached from the main LV, and will become visible and unused.\n"
+    "The replacement LV will be attached to the main LV, becoming\n"
+    "a hidden cachevol, and used by the main LV for caching.\n")
+
 arg(reportformat_ARG, '\0', "reportformat", reportformat_VAL, 0, 0,
     "Overrides current output format for reports which is defined globally by\n"
     "the report/output_format setting in lvm.conf.\n"
diff --git a/tools/command-lines.in b/tools/command-lines.in
index 03cf3452b..82b27ae63 100644
--- a/tools/command-lines.in
+++ b/tools/command-lines.in
@@ -728,6 +728,8 @@ DESC: Repair a cache pool.
 RULE: all not lv_is_locked lv_is_pvmove
 RULE: --poolmetadataspare and LV_cache LV_cachepool LV_thinpool
 
+---
+
 lvconvert --repaircachevol LV LV
 OO: OO_LVCONVERT
 ID: lvconvert_repair_cachevol
@@ -736,6 +738,16 @@ DESC: write repaired metadata to the destination LV (in first
 DESC: position arg), and copy cache data from the cachevol to
 DESC: the destination LV.
 
+lvconvert --replacecachevol LV LV
+OO: OO_LVCONVERT
+ID: lvconvert_replace_cachevol
+DESC: Replace the specified cachevol LV with the LV named
+DESC: in the first position arg. The replacement LV should
+DESC: hold a repaired copy of the cache. The LV that was
+DESC: using cachevol for caching will use the replacement.
+
+---
+
 lvconvert --replace PV LV_raid
 OO: OO_LVCONVERT
 OP: PV ...
diff --git a/tools/lvconvert.c b/tools/lvconvert.c
index b735c86e3..145948a91 100644
--- a/tools/lvconvert.c
+++ b/tools/lvconvert.c
@@ -4312,6 +4312,159 @@ int lvconvert_repair_cachevol_cmd(struct cmd_context *cmd, int argc, char **argv
 	return ret;
 }
 
+static int _lvconvert_replace_cachevol_single(struct cmd_context *cmd,
+					struct logical_volume *lv,
+					struct processing_handle *handle)
+{
+	struct volume_group *vg = lv->vg;
+	struct logical_volume *cache_lv = NULL, *cachevol_lv, *lv_fast_old, *lv_fast_new;
+	struct lv_segment *cache_seg = first_seg(lv);
+	struct lv_list *lvl;
+	const char *cachevol_name;
+
+	lv_fast_new = lv;
+	lv = NULL;
+
+	/* command def should prevent this */
+	if (!(cachevol_name = arg_str_value(cmd, replacecachevol_ARG, "")))
+		return_ECMD_FAILED;
+
+	if (!validate_lvname_param(cmd, &vg->name, &cachevol_name)) {
+		log_error("Invalid cachevol LV name %s.", cachevol_name);
+		return ECMD_FAILED;
+	}
+
+	if (!(cachevol_lv = find_lv(vg, cachevol_name))) {
+		log_error("Failed to find cachevol LV %s.", cachevol_name);
+		return ECMD_FAILED;
+	}
+
+	if (!lv_is_cache_vol(cachevol_lv)) {
+		log_error("LV %s is not a cachevol.", display_lvname(cachevol_lv));
+		return 0;
+	}
+
+	/*
+	 * Find the cache LV using the cachevol.
+	 */
+	dm_list_iterate_items(lvl, &vg->lvs) {
+		if (!lv_is_cache(lvl->lv))
+			continue;
+
+		if (!(cache_seg = first_seg(lvl->lv)))
+			continue;
+
+		if (!lv_is_cache_vol(cache_seg->pool_lv))
+			continue;
+
+		if (cache_seg->pool_lv != cachevol_lv)
+			continue;
+
+		cache_lv = lvl->lv;
+		break;
+	}
+
+	if (!cache_lv) {
+		log_error("Failed to find LV using cachevol %s.", display_lvname(cachevol_lv));
+		return ECMD_FAILED;
+	}
+
+	if (lv_is_active(cache_lv)) {
+		log_error("LV %s must be inactive.", display_lvname(cache_lv));
+		return ECMD_FAILED;
+	}
+
+	if (lv_is_active(cachevol_lv)) {
+		log_error("LV %s must be inactive.", display_lvname(cachevol_lv));
+		return ECMD_FAILED;
+	}
+
+	if (lv_is_active(lv_fast_new)) {
+		log_error("LV %s must be inactive.", display_lvname(lv_fast_new));
+		return ECMD_FAILED;
+	}
+
+	if (!dm_list_empty(&lv_fast_new->segs_using_this_lv)) {
+		log_error("LV %s is already in use.", display_lvname(lv_fast_new));
+		return ECMD_FAILED;
+	}
+
+	if (vg_is_shared(vg)) {
+		/* cache LV using the cachevol cannot be active elsewhere */
+		if (!lockd_lv(cmd, cache_lv, "ex", 0))
+			return_ECMD_FAILED;
+
+		/* current cachevol LV cannot be active elsewhere. */
+		if (!lockd_lv(cmd, cachevol_lv, "ex", 0))
+			return_ECMD_FAILED;
+
+		/* replacement LV cannot be elsewhere. */
+		if (!lockd_lv(cmd, lv_fast_new, "ex", 0))
+			return_ECMD_FAILED;
+	}
+
+	if (!arg_is_set(cmd, yes_ARG) &&
+	    yes_no_prompt("Replace current cachevol %s with %s for caching %s? [y/n]: ",
+		    	  cachevol_lv->name,
+			  lv_fast_new->name,
+			  display_lvname(cache_lv)) == 'n') {
+		return ECMD_FAILED;
+	}
+
+	if (!archive(vg))
+		return_0;
+
+	/* remove cachevol_lv from the cachevol role */
+	remove_seg_from_segs_using_this_lv(cachevol_lv, cache_seg);
+	cachevol_lv->status &= ~LV_CACHE_VOL;
+	lv_set_visible(cachevol_lv);
+	lv_fast_old = cachevol_lv;
+	cachevol_lv = NULL;
+
+	/* put lv_fast_new into the cachevol role */
+	lv_fast_new->status |= LV_CACHE_VOL;
+	cache_seg->pool_lv = lv_fast_new;
+	add_seg_to_segs_using_this_lv(lv_fast_new, cache_seg);
+	lv_set_hidden(lv_fast_new);
+
+	if (!vg_write(vg) || !vg_commit(vg))
+		return_0;
+
+	log_print("LV %s is now using cachevol %s for caching.",
+		  display_lvname(cache_lv), display_lvname(lv_fast_new));
+	log_print("The previous cachevol %s is now unused.", display_lvname(lv_fast_old));
+
+	backup(vg);
+	return 1;
+}
+
+int lvconvert_replace_cachevol_cmd(struct cmd_context *cmd, int argc, char **argv)
+{
+
+	struct processing_handle *handle;
+	struct lvconvert_result lr = { 0 };
+	int ret;
+
+	if (!(handle = init_processing_handle(cmd, NULL))) {
+		log_error("Failed to initialize processing handle.");
+		return ECMD_FAILED;
+	}
+
+	handle->custom_handle = &lr;
+
+	cmd->cname->flags &= ~GET_VGNAME_FROM_OPTIONS;
+
+	ret = process_each_lv(cmd, cmd->position_argc, cmd->position_argv, NULL, NULL, READ_FOR_UPDATE, handle, NULL,
+			      &_lvconvert_replace_cachevol_single);
+
+	destroy_processing_handle(cmd, handle);
+
+	if (!ret)
+		log_error("Cache volume not replaced.");
+
+	return ret;
+}
+
 static int _lvconvert_replace_pv_single(struct cmd_context *cmd, struct logical_volume *lv,
 			struct processing_handle *handle)
 {
diff --git a/tools/lvmcmdline.c b/tools/lvmcmdline.c
index 6d308b6d2..24c37d292 100644
--- a/tools/lvmcmdline.c
+++ b/tools/lvmcmdline.c
@@ -133,6 +133,7 @@ static const struct command_function _command_functions[CMD_COUNT] = {
 	{ lvconvert_split_and_keep_cache_CMD,		lvconvert_split_cache_cmd },
 	{ lvconvert_split_and_remove_cache_CMD,		lvconvert_split_cache_cmd },
 	{ lvconvert_repair_cachevol_CMD,		lvconvert_repair_cachevol_cmd },
+	{ lvconvert_replace_cachevol_CMD,		lvconvert_replace_cachevol_cmd },
 
 	/* lvconvert raid-related type conversions */
 	{ lvconvert_raid_types_CMD,			lvconvert_raid_types_cmd },
diff --git a/tools/tools.h b/tools/tools.h
index 0064d018d..59c61bd7f 100644
--- a/tools/tools.h
+++ b/tools/tools.h
@@ -261,6 +261,7 @@ int lvconvert_to_pool_or_swap_metadata_cmd(struct cmd_context *cmd, int argc, ch
 int lvconvert_merge_thin_cmd(struct cmd_context *cmd, int argc, char **argv);
 int lvconvert_split_cache_cmd(struct cmd_context *cmd, int argc, char **argv);
 int lvconvert_repair_cachevol_cmd(struct cmd_context *cmd, int argc, char **argv);
+int lvconvert_replace_cachevol_cmd(struct cmd_context *cmd, int argc, char **argv);
 
 int lvconvert_raid_types_cmd(struct cmd_context * cmd, int argc, char **argv);
 int lvconvert_split_mirror_images_cmd(struct cmd_context * cmd, int argc, char **argv);