Add and track an "ondisk" pointer to struct volume_group.

This allows us to get the current on-disk version of the metadata whenever we
have the current in-flight version, without a recourse to scanning or lvmcache.

lib/metadata/lv.h

@@ -90,4 +90,5 @@ int lv_active_change(struct cmd_context *cmd, struct logical_volume *lv,
 		     enum activation_change activate);
 char *lv_active_dup(struct dm_pool *mem, const struct logical_volume *lv);
 const struct logical_volume *lv_lock_holder(const struct logical_volume *lv);
+struct logical_volume *lv_ondisk(struct logical_volume *lv);
 #endif /* _LVM_LV_H */

lib/metadata/metadata.c

@@ -831,6 +831,21 @@ int vgcreate_params_validate(struct cmd_context *cmd,
 	return 1;
 }
 
+static int _vg_update_vg_ondisk(struct volume_group *vg)
+{
+	struct dm_config_tree *cft;
+	if (vg->vg_ondisk) /* we already have it */
+		return 1;
+
+	cft = export_vg_to_config_tree(vg);
+	if (!cft)
+		return 0;
+
+	vg->vg_ondisk = import_vg_from_config_tree(cft, vg->fid);
+	dm_config_destroy(cft);
+	return 1;
+}
+
 /*
  * Create a (struct volume_group) volume group handle from a struct volume_group pointer and a
  * possible failure code or zero for success.
@@ -839,6 +854,7 @@ static struct volume_group *_vg_make_handle(struct cmd_context *cmd,
 					    struct volume_group *vg,
 					    uint32_t failure)
 {
+
 	/* Never return a cached VG structure for a failure */
 	if (vg && vg->vginfo && failure != SUCCESS) {
 		release_vg(vg);
@@ -848,6 +864,9 @@ static struct volume_group *_vg_make_handle(struct cmd_context *cmd,
 	if (!vg && !(vg = alloc_vg("vg_make_handle", cmd, NULL)))
 		return_NULL;
 
+	if (vg->fid && !_vg_update_vg_ondisk(vg))
+		vg->read_status |= FAILED_ALLOCATION;
+
 	if (vg->read_status != failure)
 		vg->read_status = failure;
 
@@ -2690,6 +2709,12 @@ int vg_commit(struct volume_group *vg)
 		 * The volume_group structure could be reused later.
 		 */
 		vg->old_name = NULL;
+
+		/* This *is* the original now that it's commited. */
+		release_vg(vg->vg_ondisk);
+		vg->vg_ondisk = NULL;
+		if (!_vg_update_vg_ondisk(vg)) /* make a new one for future edits */
+			return_0;
 	}
 
 	/* If update failed, remove any cached precommitted metadata. */
@@ -4523,3 +4548,25 @@ char *tags_format_and_copy(struct dm_pool *mem, const struct dm_list *tags)
 	}
 	return dm_pool_end_object(mem);
 }
+
+struct logical_volume *lv_ondisk(struct logical_volume *lv)
+{
+	struct volume_group *vg;
+	struct lv_list *lvl;
+
+	if (!lv)
+		return NULL;
+
+	vg = lv->vg;
+
+	if (vg->vg_ondisk)
+		vg = vg->vg_ondisk;
+
+	dm_list_iterate_items(lvl, &vg->lvs)
+		if (!strncmp(lvl->lv->lvid.s, lv->lvid.s, sizeof(lv->lvid)))
+			return lvl->lv;
+
+	log_error(INTERNAL_ERROR "LV %s/%s (UUID %s) not found in ondisk metadata.",
+		  lv->vg->name, lv->name, lv->lvid.s);
+	return NULL;
+}

lib/metadata/vg.c

@@ -87,6 +87,7 @@ void release_vg(struct volume_group *vg)
 	    !lvmcache_vginfo_holders_dec_and_test_for_zero(vg->vginfo))
 		return;
 
+	release_vg(vg->vg_ondisk);
 	_free_vg(vg);
 }
 

lib/metadata/vg.h

@@ -48,6 +48,15 @@ struct volume_group {
 	uint32_t cmd_missing_vgs;/* Flag marks missing VG */
 	uint32_t seqno;		/* Metadata sequence number */
 
+	/*
+	 * The parsed on-disk copy of this VG; is NULL if this is the on-disk
+	 * version (i.e. vg_ondisk == NULL *implies* this is the on-disk copy,
+	 * there is no guarantee that if this VG is the same as the on-disk one
+	 * this will be NULL). The pointer is maintained by calls to
+	 * _vg_update_vg_ondisk.
+	 */
+	struct volume_group *vg_ondisk;
+
 	alloc_policy_t alloc;
 	uint64_t status;