Fix lv_count when manipulating with snapshots and max_lv is set.

Patch fixes these problems:
 - during the snapshot creation process, it needs create 2 LVs,
   one is cow, second becomes snapshot.
   If the code fails in vg_add_snapshot, code lvcreate will not remove
   LV cow volume.

 - if max_lv is set and VG contains snapshot, it can happen that
   during the activation lv_count is temporarily increased over the limit
   and VG metadata are not properly processed
   see https://bugzilla.redhat.com/show_bug.cgi?id=490298

 - vgcfgrestore alows restore with max_lv set to lower valuer that actual
   LV count. This later leads to situation that max_lv is completely ignored.

 - vgck doesn't call vg_validate(). It should at least try:-)

Signed-off-by: Milan Broz <mbroz@redhat.com>

WHATS_NEW

@@ -1,5 +1,7 @@
 Version 2.02.46 - 
 ================================
+  Fix maximal volume count check for snapshots if max_lv set for volume group.
+  Fix lvcreate to remove cow volume if the snapshot creation fails.
   Fix error messages when PV uuid or pe_start reading fails.
   Rename liblvm.a to liblvm-internal.a and build new application library.
   Flush memory pool and fix locking in clvmd refresh and backup command.

lib/metadata/metadata.c

@@ -1461,6 +1461,13 @@ int vg_validate(struct volume_group *vg)
 		r = 0;
 	}
 
+	if (vg->max_lv && (vg->max_lv < vg->lv_count)) {
+		log_error("Internal error: Volume group %s contains %u volumes"
+			  " but the limit is set to %u.",
+			  vg->name, vg->lv_count, vg->max_lv);
+		r = 0;
+	}
+
 	return r;
 }
 

lib/metadata/snapshot_manip.c

@@ -76,10 +76,18 @@ int vg_add_snapshot(const char *name, struct logical_volume *origin,
 		return 0;
 	}
 
+	/*
+	 * Set origin lv count in advance to prevent fail because
+	 * of temporary violation of LV limits.
+	 */
+	origin->vg->lv_count--;
+
 	if (!(snap = lv_create_empty(name ? name : "snapshot%d",
 				     lvid, LVM_READ | LVM_WRITE | VISIBLE_LV,
-				     ALLOC_INHERIT, 1, origin->vg)))
+				     ALLOC_INHERIT, 1, origin->vg))) {
+		origin->vg->lv_count++;
 		return_0;
+	}
 
 	snap->le_count = extent_count;
 
@@ -93,7 +101,6 @@ int vg_add_snapshot(const char *name, struct logical_volume *origin,
 
 	origin->origin_count++;
 	origin->vg->snapshot_count++;
-	origin->vg->lv_count--;
 	cow->snapshot = seg;
 
 	cow->status &= ~VISIBLE_LV;

test/t-lvcreate-usage.sh

@@ -58,3 +58,12 @@ not lvcreate -L 64M -n $lv -i2 --stripesize 3 $vg 2>err
 grep "^  Invalid stripe size 3\.00 KB\$" err
 case $(lvdisplay $vg) in "") true ;; *) false ;; esac
 
+# Setting max_lv works. (bz490298)
+vgchange -l 4 $vg
+lvcreate -l1 -n $lv1 $vg
+lvcreate -l1 -s -n $lv2 $vg/$lv1
+lvcreate -l1 -n $lv3 $vg
+not lvcreate -l1 -n $lv4 $vg
+vgs $vg
+lvremove -ff $vg
+vgchange -l 0 $vg

tools/lvcreate.c

@@ -836,7 +836,7 @@ static int _lvcreate(struct cmd_context *cmd, struct volume_group *vg,
 		if (!vg_add_snapshot(NULL, org, lv, NULL,
 				     org->le_count, lp->chunk_size)) {
 			log_error("Couldn't create snapshot.");
-			return 0;
+			goto deactivate_and_revert_new_lv;
 		}
 
 		/* store vg on disk(s) */

tools/vgck.c

@@ -33,6 +33,9 @@ static int vgck_single(struct cmd_context *cmd __attribute((unused)),
 	if (!vg_check_status(vg, EXPORTED_VG))
 		return ECMD_FAILED;
 
+	if (!vg_validate(vg))
+		return ECMD_FAILED;
+
 	return ECMD_PROCESSED;
 }