Make Assemble/Force work on raid6 with 2 missing devices.

Previously it onl worked when one missing device.
Also split the "force" update_super method into two and it
is really serving two functions.

Assemble.c

@@ -656,7 +656,9 @@ int Assemble(struct supertype *st, char *mddev, int mdfd,
 			continue;
 		}
 		info.events = devices[most_recent].events;
-		st->ss->update_super(&info, super, "force", devices[chosen_drive].devname, verbose, 0, NULL);
+		st->ss->update_super(&info, super, "force-one",
+				     devices[chosen_drive].devname, verbose,
+				     0, NULL);
 
 		if (st->ss->store_super(st, fd, super)) {
 			close(fd);
@@ -752,10 +754,10 @@ int Assemble(struct supertype *st, char *mddev, int mdfd,
 		}
 #endif
 	}
-	if (force && okcnt == info.array.raid_disks-1) {
-		/* FIXME check event count */
-		change += st->ss->update_super(&info, super, "force",
-					devices[chosen_drive].devname, verbose, 0, NULL);
+	if (force && okcnt < info.array.raid_disks) {
+		change += st->ss->update_super(&info, super, "force-array",
+					devices[chosen_drive].devname, verbose,
+					       0, NULL);
 	}
 
 	if (change) {

ChangeLog

@@ -2,6 +2,10 @@ Changes Prior to this release
     -   Fixed UUID printing in "--detail --brief" for version1 metadata.
     -   --update=resync did exactly the wrong thing for version1 metadata.
 	It caused a resync to not happen, rather than to happen.
+    -   Allow --assemble --force to mark a raid6 clean when it has two
+	missing devices (which is needed else if won't assemble.
+	Without this fix it would only assemble if one or zero
+	missing devices.
 
 Changes Prior to 2.5.6 release
     -   Fix bug which meant "bitmap=xxx" in mdadm.conf was not handled

super0.c

@@ -411,13 +411,21 @@ static int update_super0(struct mdinfo *info, void *sbv, char *update,
 			} else if (i >= sb->raid_disks && sb->disks[i].number == 0)
 				sb->disks[i].state = 0;
 	}
-	if (strcmp(update, "force")==0) {
+	if (strcmp(update, "force-one")==0) {
+		/* Not enough devices for a working array, so
+		 * bring this one up-to-date.
+		 */
 		__u32 ehi = sb->events_hi, elo = sb->events_lo;
 		sb->events_hi = (info->events>>32) & 0xFFFFFFFF;
 		sb->events_lo = (info->events) & 0xFFFFFFFF;
 		if (sb->events_hi != ehi ||
 		    sb->events_lo != elo)
 			rv = 1;
+	}
+	if (strcmp(update, "force-array")==0) {
+		/* degraded array and 'force' requested, so
+		 * maybe need to mark it 'clean'
+		 */
 		if ((sb->level == 5 || sb->level == 4 || sb->level == 6) &&
 		    (sb->state & (1 << MD_SB_CLEAN)) == 0) {
 			/* need to force clean */

super1.c

@@ -485,10 +485,18 @@ static int update_super1(struct mdinfo *info, void *sbv, char *update,
 	int rv = 0;
 	struct mdp_superblock_1 *sb = sbv;
 
-	if (strcmp(update, "force")==0) {
+	if (strcmp(update, "force-one")==0) {
+		/* Not enough devices for a working array,
+		 * so bring this one up-to-date
+		 */
 		if (sb->events != __cpu_to_le64(info->events))
 			rv = 1;
 		sb->events = __cpu_to_le64(info->events);
+	}
+	if (strcmp(update, "force-array")==0) {
+		/* Degraded array and 'force' requests to
+		 * maybe need to mark it 'clean'.
+		 */
 		switch(__le32_to_cpu(sb->level)) {
 		case 5: case 4: case 6:
 			/* need to force clean */