metadata: move vg parsing to vg_write

Parsing vg structure during  supend/commit/resume may require a lot of
memory - so move this into vg_write.

FIXME: there are now multiple cache layers which our doing some thing
multiple times at different levels. Moreover there is now different
caching path with and without lvmetad - this should be unified
and both path should use same mechanism.

WHATS_NEW

@@ -1,5 +1,6 @@
 Version 2.02.106 - 
 ====================================
+  Move parsing of VG metadata from vg_commit() back to vg_write() (2.02.99)
   Avoid a PV label scan while in a critical section.
   Remove (always 0) skip argument from lv_activation_skip().
   Create /dev/disk/by-id/lvm-pv-uuid-<PV_UUID> symlink for each PV via udev.

lib/metadata/metadata.c

@@ -856,30 +856,45 @@ int vgcreate_params_validate(struct cmd_context *cmd,
 	return 1;
 }
 
-static int _vg_update_vg_ondisk(struct volume_group *vg)
+/*
+ * Update content of precommitted VG
+ *
+ * TODO: Optimize in the future, since lvmetad needs similar
+ *       config tree processing in lvmetad_vg_update().
+ */
+static int _vg_update_vg_precommitted(struct volume_group *vg)
 {
 	struct dm_config_tree *cft;
-	int pool_locked;
+
+	release_vg(vg->vg_precommitted);
+	vg->vg_precommitted = NULL;
+
+	if (!(cft = export_vg_to_config_tree(vg)))
+		return_0;
+
+	if (!(vg->vg_precommitted = import_vg_from_config_tree(cft, vg->fid)))
+		stack;
+
+	dm_config_destroy(cft);
+
+	return vg->vg_precommitted ? 1 : 0;
+}
+
+static int _vg_update_vg_ondisk(struct volume_group *vg)
+{
+	if (dm_pool_locked(vg->vgmem))
+		return 1;
 
 	if (vg->vg_ondisk || is_orphan_vg(vg->name)) /* we already have it */
 		return 1;
 
-	pool_locked = dm_pool_locked(vg->vgmem);
+	if (!_vg_update_vg_precommitted(vg))
-	if (pool_locked && !dm_pool_unlock(vg->vgmem, 0))
 		return_0;
 
-	cft = export_vg_to_config_tree(vg);
+	vg->vg_ondisk = vg->vg_precommitted;
-	if (!cft)
+	vg->vg_precommitted = NULL;
-		return 0;
 
-	vg->vg_ondisk = import_vg_from_config_tree(cft, vg->fid);
+	return 1;
-	dm_config_destroy(cft);
-
-	/* recompute the pool crc */
-	if (pool_locked && !dm_pool_lock(vg->vgmem, 1))
-		return_0;
-
-	return vg->vg_ondisk ? 1 : 0;
 }
 
 /*
@@ -2687,6 +2702,9 @@ int vg_write(struct volume_group *vg)
 	if (!(vg->fid->fmt->features & FMT_PRECOMMIT) && !lvmetad_vg_update(vg))
 		return_0;
 
+	if (!_vg_update_vg_precommitted(vg)) /* prepare precommited */
+		return_0;
+
 	return 1;
 }
 
@@ -2753,9 +2771,8 @@ int vg_commit(struct volume_group *vg)
 
 		/* This *is* the original now that it's commited. */
 		release_vg(vg->vg_ondisk);
-		vg->vg_ondisk = NULL;
+		vg->vg_ondisk = vg->vg_precommitted;
-		if (!_vg_update_vg_ondisk(vg)) /* make a new one for future edits */
+		vg->vg_precommitted = NULL;
-			return_0;
 	}
 
 	/* If update failed, remove any cached precommitted metadata. */
@@ -2772,6 +2789,9 @@ void vg_revert(struct volume_group *vg)
 {
 	struct metadata_area *mda;
 
+	release_vg(vg->vg_precommitted);  /* VG is no longer needed */
+	vg->vg_precommitted = NULL;
+
 	dm_list_iterate_items(mda, &vg->fid->metadata_areas_in_use) {
 		if (mda->ops->vg_revert &&
 		    !mda->ops->vg_revert(vg->fid, vg, mda)) {

lib/metadata/vg.c

@@ -89,6 +89,7 @@ void release_vg(struct volume_group *vg)
 		return;
 
 	release_vg(vg->vg_ondisk);
+	release_vg(vg->vg_precommitted);
 	_free_vg(vg);
 }
 

lib/metadata/vg.h

@@ -57,6 +57,7 @@ struct volume_group {
 	 * _vg_update_vg_ondisk.
 	 */
 	struct volume_group *vg_ondisk;
+	struct volume_group *vg_precommitted; /* Parsed from precommitted */
 
 	alloc_policy_t alloc;
 	struct profile *profile;