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[lvm-devel] [LVM PATCH 2/6] cache: Add functions that create/remove cache LVs



A cache LV - from LVM's perpective - is a user accessible device that
links the cachepool LV and the origin LV.  The following functions
were added to facilitate the creation and removal of this top-level
LV:
1) 'lv_cache_create' - takes a cachepool and an origin device and links
   them into a new top-level LV of 'cache' segment type.  No allocation
   is necessary in this function, as the sub-LVs contain all of the
   necessary allocated space.  Only the top-level layer needs to be
   created.

2) 'lv_cache_remove' - this function removes the top-level LV of a
   cache LV - promoting the cachepool and origin sub-LVs to top-level
   devices and leaving them exposed to the user.  That is, the
   cachepool is unlinked and free to be used with another origin to
   form a new cache LV; and the origin is no longer cached.
---
 lib/Makefile.in                  |    1 +
 lib/metadata/cache_manip.c       |  219 ++++++++++++++++++++++++++++++++++++++
 lib/metadata/metadata-exported.h |    9 ++-
 3 files changed, 227 insertions(+), 2 deletions(-)
 create mode 100644 lib/metadata/cache_manip.c

diff --git a/lib/Makefile.in b/lib/Makefile.in
index 3808269..968ad00 100644
--- a/lib/Makefile.in
+++ b/lib/Makefile.in
@@ -87,6 +87,7 @@ SOURCES =\
 	locking/locking.c \
 	locking/no_locking.c \
 	log/log.c \
+	metadata/cache_manip.c \
 	metadata/lv.c \
 	metadata/lv_manip.c \
 	metadata/merge.c \
diff --git a/lib/metadata/cache_manip.c b/lib/metadata/cache_manip.c
new file mode 100644
index 0000000..cfe3ce6
--- /dev/null
+++ b/lib/metadata/cache_manip.c
@@ -0,0 +1,219 @@
+/*
+ * Copyright (C) 2014 Red Hat, Inc. All rights reserved.
+ *
+ * This file is part of LVM2.
+ *
+ * This copyrighted material is made available to anyone wishing to use,
+ * modify, copy, or redistribute it subject to the terms and conditions
+ * of the GNU Lesser General Public License v.2.1.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include "lib.h"
+#include "metadata.h"
+#include "locking.h"
+#include "pv_map.h"
+#include "lvm-string.h"
+#include "toolcontext.h"
+#include "lv_alloc.h"
+#include "pv_alloc.h"
+#include "display.h"
+#include "segtype.h"
+#include "archiver.h"
+#include "activate.h"
+#include "str_list.h"
+#include "defaults.h"
+#include "lvm-exec.h"
+
+/*
+ * lv_cache_create
+ * @pool
+ * @origin
+ *
+ * Given a cache_pool and an origin, link the two and create a
+ * cached LV.
+ *
+ * Returns: cache LV on success, NULL on failure
+ */
+struct logical_volume *lv_cache_create(struct logical_volume *pool,
+				       struct logical_volume *origin)
+{
+	const struct segment_type *segtype;
+	struct cmd_context *cmd = pool->vg->cmd;
+	struct logical_volume *cache_lv;
+	struct lv_segment *seg;
+
+	if (!lv_is_cache_pool(pool)) {
+		log_error(INTERNAL_ERROR
+			  "%s is not a cache_pool LV", pool->name);
+		return NULL;
+	}
+
+	if (lv_is_cache_type(origin)) {
+		/*
+		 * FIXME: We can layer caches, insert_layer_for_lv() would
+		 * have to do a better job renaming the LVs in the stack
+		 * first so that there isn't a name collision with <name>_corig.
+		 * The origin under the origin would become *_corig_corig
+		 * before renaming the origin above to *_corig.
+		 */
+		log_error(INTERNAL_ERROR
+			  "The origin, %s, cannot be of cache type",
+			  origin->name);
+		return NULL;
+	}
+
+	if (!(segtype = get_segtype_from_string(cmd, "cache")))
+		return_NULL;
+
+	cache_lv = origin;
+	if (!(origin = insert_layer_for_lv(cmd, cache_lv, CACHE, "_corig")))
+		return_NULL;
+
+	seg = first_seg(cache_lv);
+	seg->segtype = segtype;
+
+	if (!attach_pool_lv(seg, pool, NULL, NULL))
+		return_0;
+
+	return cache_lv;
+}
+
+/*
+ * lv_cache_remove
+ * @cache_lv
+ *
+ * Given a cache LV, remove the cache layer.  This will unlink
+ * the origin and cache_pool, remove the cache LV layer, and promote
+ * the origin to a usable non-cached LV of the same name as the
+ * given cache_lv.
+ *
+ * Returns: 1 on success, 0 on failure
+ */
+int lv_cache_remove(struct logical_volume *cache_lv)
+{
+	struct cmd_context *cmd = cache_lv->vg->cmd;
+	char *policy_name;
+	uint64_t dirty_blocks;
+	struct segment_type *segtype;
+	struct lv_segment *cache_seg = first_seg(cache_lv);
+	struct logical_volume *origin_lv;
+	struct logical_volume *cache_pool_lv;
+
+	if (!lv_is_cache(cache_lv))
+		return_0;
+
+	/*
+	 * FIXME:
+	 * Before the link can be broken, we must ensure that the
+	 * cache has been flushed.  This may already be the case
+	 * if the cache mode is writethrough (or the cleaner
+	 * policy is in place from a previous half-finished attempt
+	 * to remove the cache_pool).  It could take a long time to
+	 * flush the cache - it should probably be done in the background.
+	 *
+	 * Also, if we do perform the flush in the background and we
+	 * happen to also be removing the cache/origin LV, then we
+	 * could check if the cleaner policy is in place and simply
+	 * remove the cache_pool then without waiting for the flush to
+	 * complete.
+	 */
+	if (!lv_cache_policy_info(cache_lv, &policy_name, NULL, NULL))
+		return_0;
+
+	if (strcmp(policy_name, "cleaner")) {
+		/* We must swap in the cleaner to flush the cache */
+		log_error("Flushing cache for %s", cache_lv->name);
+
+		/*
+		 * Is there are clean way to free the memory for the name
+		 * and argv when changing the policy?
+		 */
+		cache_seg->policy_name = (char *)"cleaner";
+		cache_seg->policy_argc = 0;
+		cache_seg->policy_argv = NULL;
+
+		/* update the kernel to put the cleaner policy in place */
+		if (!vg_write(cache_lv->vg))
+			return_0;
+		if (!suspend_lv(cmd, cache_lv))
+			return_0;
+		if (!vg_commit(cache_lv->vg))
+			return_0;
+		if (!resume_lv(cmd, cache_lv))
+			return_0;
+
+		//FIXME: use polling to do this...
+		do {
+			if (!lv_cache_block_info(cache_lv, NULL,
+						 &dirty_blocks, NULL, NULL))
+				return_0;
+			log_error("%" PRIu64 " blocks must still be flushed.",
+				  dirty_blocks);
+			if (dirty_blocks)
+				sleep(5);
+		} while (dirty_blocks);
+	}
+
+	cache_pool_lv = first_seg(cache_lv)->pool_lv;
+	if (!detach_pool_lv(first_seg(cache_lv)))
+		return_0;
+
+	origin_lv = seg_lv(first_seg(cache_lv), 0);
+	lv_set_visible(origin_lv);
+
+//FIXME: We should be able to use 'remove_layer_from_lv', but
+//       there is a call to 'lv_empty' in there that recursively
+//       deletes everything down the tree - including the origin_lv
+//       that we are trying to preserve!
+//	if (!remove_layer_from_lv(cache_lv, origin_lv))
+//		return_0;
+
+	if (!remove_seg_from_segs_using_this_lv(origin_lv, first_seg(cache_lv)))
+		return_0;
+	if (!move_lv_segments(cache_lv, origin_lv, 0, 0))
+		return_0;
+
+	cache_lv->status &= ~CACHE;
+
+	segtype = get_segtype_from_string(cmd, "error");
+	if (!lv_add_virtual_segment(origin_lv, 0,
+				    cache_lv->le_count, segtype, NULL))
+		return_0;
+
+	if (!vg_write(cache_lv->vg))
+		return_0;
+
+	/*
+	 * suspend_lv on this cache LV will suspend all of the components:
+	 * - the top-level cache LV
+	 * - the origin
+	 * - the cache_pool and all of its sub-LVs
+	 */
+	if (!suspend_lv(cmd, cache_lv))
+		return_0;
+
+	if (!vg_commit(cache_lv->vg))
+		return_0;
+
+	/*
+	 * resume_lv on this (former) cache LV will resume all
+	 * but the cache_pool LV.  It must be resumed seperately.
+	 */
+	if (!resume_lv(cmd, cache_lv))
+		return_0;
+	if (!resume_lv(cmd, cache_pool_lv))
+		return_0;
+
+	if (!activate_lv(cmd, origin_lv))
+		return_0;
+	if (!deactivate_lv(cmd, origin_lv))
+		return_0;
+	if (!lv_remove(origin_lv))
+		return_0;
+
+	return 1;
+}
diff --git a/lib/metadata/metadata-exported.h b/lib/metadata/metadata-exported.h
index 97f05fc..d8eef2d 100644
--- a/lib/metadata/metadata-exported.h
+++ b/lib/metadata/metadata-exported.h
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2001-2004 Sistina Software, Inc. All rights reserved.
- * Copyright (C) 2004-2013 Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2004-2014 Red Hat, Inc. All rights reserved.
  *
  * This file is part of LVM2.
  *
@@ -1016,9 +1016,14 @@ int lv_raid_reshape(struct logical_volume *lv,
 int lv_raid_replace(struct logical_volume *lv, struct dm_list *remove_pvs,
 		    struct dm_list *allocate_pvs);
 int lv_raid_remove_missing(struct logical_volume *lv);
-
 /* --  metadata/raid_manip.c */
 
+/* ++  metadata/cache_manip.c */
+struct logical_volume *lv_cache_create(struct logical_volume *pool,
+				       struct logical_volume *origin);
+int lv_cache_remove(struct logical_volume *cache_lv);
+/* --  metadata/cache_manip.c */
+
 struct cmd_vg *cmd_vg_add(struct dm_pool *mem, struct dm_list *cmd_vgs,
 			  const char *vg_name, const char *vgid,
 			  uint32_t flags);
-- 
1.7.7.6


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