tests: add case for metadata checksum differences

Cover the case where two copies of metadata have the
same seqno but different checksums.  Also elaborate
on an existing fixme in the code for this case, since
we should be doing something better for this case.

This had been uncovering an issue with reopening
fds in readwrite mode.

lib/cache/lvmcache.c

@@ -1663,6 +1663,9 @@ int lvmcache_update_vgname_and_id(struct cmd_context *cmd, struct lvmcache_info
 		 * second updated to seqno 4, first comes back and second goes
 		 * missing, first updated to seqno 4, second comes back, now
 		 * both are present with same seqno but different checksums.
+		 * FIXME: we should check if the majority of mda copies have one
+		 * checksum and if so use that copy of metadata, but if there's
+		 * not a majority, don't allow the VG to be modified/activated.
 		 */
 
 		if ((vginfo->mda_size != vgsummary->mda_size) || (vginfo->mda_checksum != vgsummary->mda_checksum)) {

test/shell/metadata-old.sh

@@ -175,3 +175,48 @@ lvs $vg/$lv4
 
 vgchange -an $vg
 vgremove -ff $vg
+
+# Test when the metadata on two PVs have the same seqno
+# but different checksums.
+
+dd if=/dev/zero of="$dev1" || true
+dd if=/dev/zero of="$dev2" || true
+
+pvcreate "$dev1"
+pvcreate "$dev2"
+
+vgcreate $SHARED $vg "$dev1" "$dev2"
+
+lvcreate -n $lv1 -l1 -an $vg
+
+pvck --dump metadata -f meta "$dev2"
+
+# change an unimportant character so the metadata is effectively
+# the same in content but will have a different checksum
+sed 's/Linux/linux/' meta > meta2
+
+# write out the changed metadata
+pvck --repair -y -f meta2 "$dev2"
+
+# the vg can still be used but will produce warnings
+# the mda on one pv is updated, but not the other,
+# which changes the error from a checksum inconsistency
+# into a seqno inconsistency.
+lvs $vg 2>&1 | tee out
+grep WARNING out
+grep $lv1 out
+lvcreate -n $lv2 -l1 -an $vg 2>&1 |tee out
+grep WARNING out
+lvs $vg 2>&1 | tee out
+grep WARNING out
+grep $lv1 out
+grep $lv2 out
+
+# correct the senqo inconsistency
+vgck --updatemetadata $vg
+lvs $vg 2>&1 | tee out
+not grep WARNING out
+grep $lv1 out
+grep $lv2 out
+
+vgremove -ff $vg

test/shell/pvck-repair.sh

@@ -399,8 +399,6 @@ lvcreate -l1 -an $vg
 # One PV, one mda, pv_header zeroed, unmatching dev name requires specified uuid
 _clear_devs "$dev1" "$dev2"
 vgcreate $vg "$dev1"
-#!!! FIXME: with this hits INTERNAL_ERROR
-#!!! vgcreate $vg "$dev1" "$dev2"
 pvck --dump headers "$dev1" || true
 UUID1=`pvck --dump headers "$dev1" | grep pv_header.pv_uuid | awk '{print $2}'`
 echo $UUID1