Support fixing of byte-swapped superblocks.

Good for moving between little-endian and big-endian.
Still needs documentation.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>

Assemble.c

@@ -334,6 +334,9 @@ int Assemble(struct supertype *st, char *mddev, int mdfd,
 		free(super);
 	super = NULL;
 
+	if (update && strcmp(update, "byteorder")==0)
+		st->minor_version = 90;
+
 	if (devcnt == 0) {
 		fprintf(stderr, Name ": no devices found for %s\n",
 			mddev);

ChangeLog

@@ -1,3 +1,7 @@
+Changes Prior to this release
+    -   Support assembling from byte-swapped superblocks
+	metadata type "0.swap" and --update=byteorder
+
 Changes Prior to 2.0-devel-3 release
     -   Assorted fixes for multiple bugs...
     -   Add test suite

mdadm.8

@@ -525,6 +525,7 @@ argument given to this flag can be one of
 .BR sparc2.2 ,
 .BR summaries ,
 .BR resync ,
+.BR byteorder ,
 or
 .BR super-minor .
 
@@ -555,6 +556,18 @@ copies for raid1) may be incorrect.  This will cause the raid system
 to perform a "resync" pass to make sure that all redundant information
 is correct.
 
+The
+.B byteorder
+option allows arrays to be moved between machines with different
+byte-order.
+When assembling such an array for the first time after a move, giving 
+.B "--update=byteorder"
+will cause
+.I mdadm
+to expect superblocks to have their byteorder reversed, and will
+correct that order before assembling the array.  This is only valid
+with original (Verion 0.90) superblocks.
+
 The
 .B summaries
 option will correct the summaries in the superblock. That is the

mdadm.c

@@ -547,6 +547,20 @@ int main(int argc, char *argv[])
 				continue;
 			if (strcmp(update, "resync")==0)
 				continue;
+			if (strcmp(update, "byteorder")==0) {
+				if (ss) {
+					fprintf(stderr, Name ": must not set metadata type with --update=byteorder.\n");
+					exit(2);
+				}
+				for(i=0; !ss && superlist[i]; i++) 
+					ss = superlist[i]->match_metadata_desc("0.swap");
+				if (!ss) {
+					fprintf(stderr, Name ": INTERNAL ERROR cannot find 0.swap\n");
+					exit(2);
+				}
+
+				continue;
+			}
 			fprintf(stderr, Name ": '--update %s' invalid.  Only 'sparc2.2', 'super-minor', 'resync' or 'summaries' supported\n",update);
 			exit(2);
 

super0.c

@@ -52,7 +52,39 @@ static unsigned long calc_sb0_csum(mdp_super_t *super)
 	return newcsum;
 }
 
+
+void super0_swap_endian(struct mdp_superblock_s *sb)
+{
+	/* as super0 superblocks are host-endian, it is sometimes
+	 * useful to be able to swap the endianness 
+	 * as (almost) everything is u32's we byte-swap every 4byte
+	 * number.
+	 * We then also have to swap the events_hi and events_lo
+	 */
+	char *sbc = (char *)sb;
+	__u32 t32;
+	int i;
+
+	for (i=0; i < MD_SB_BYTES ; i+=4) {
+		char t = sbc[i];
+		sbc[i] = sbc[i+3];
+		sbc[i+3] = t;
+		t=sbc[i+1];
+		sbc[i+1]=sbc[i+2];
+		sbc[i+2]=t;
+	}
+	t32 = sb->events_hi;
+	sb->events_hi = sb->events_lo;
+	sb->events_lo = t32;
+
+	t32 = sb->cp_events_hi;
+	sb->cp_events_hi = sb->cp_events_lo;
+	sb->cp_events_lo = t32;
+
+}	
+
 #ifndef MDASSEMBLE
+
 static void examine_super0(void *sbv)
 {
 	mdp_super_t *sb = sbv;
@@ -572,6 +604,9 @@ static int load_super0(struct supertype *st, int fd, void **sbp, char *devname)
 		return 1;
 	}
 
+	if (st->ss && st->minor_version == 9)
+		super0_swap_endian(super);
+
 	if (super->md_magic != MD_SB_MAGIC) {
 		if (devname)
 			fprintf(stderr, Name ": No super block found on %s (Expected magic %08x, got %08x)\n",
@@ -611,6 +646,10 @@ static struct supertype *match_metadata_desc0(char *arg)
 		)
 		return st;
 
+	st->minor_version = 9; /* flag for 'byte-swapped' */
+	if (strcmp(arg, "0.swap")==0)
+		return st;
+
 	free(st);
 	return NULL;
 }
@@ -742,7 +781,6 @@ int write_bitmap0(struct supertype *st, int fd, void *sbv)
 
 	return rv;
 }
-	
 
 struct superswitch super0 = {
 #ifndef MDASSEMBLE

test

@@ -28,7 +28,7 @@ export md0=/dev/md0 md1=/dev/md1 md2=/dev/md2
 # We test mdadm on loop-back block devices.
 # dir for storing files should be settable by command line maybe
 targetdir=/tmp
-export targetdir
+export targetdir dir
 size=20000
 mdsize0=19904
 mdsize1=19992

tests/06r5swap

@@ -0,0 +1,22 @@
+set -e
+
+# make a raid5 array, byte swap the superblocks, then assemble...
+
+$mdadm -CR $md0 -l5 -n4 $dev0 $dev1 $dev2 $dev3
+sleep 4
+$mdadm -S $md0
+
+$mdadm -E --metadata=0 $dev1 | grep -v Events > $targetdir/d1
+for d in $dev0 $dev1 $dev2 $dev3
+do $dir/swap_super $d
+done
+$mdadm -E --metadata=0.swap  $dev1 | grep -v Events > $targetdir/d1s
+diff -u $targetdir/d1 $targetdir/d1s
+
+$mdadm --assemble --update=byteorder $md0 $dev0 $dev1 $dev2 $dev3
+sleep 3
+cat /proc/mdstat
+exit 1
+
+
+