Add --data-offset flag for Create and Grow

This can be used to over-ride the automatic assignment of
data offset.
For --create, it is useful to re-create old arrays where different
   defaults applied.
For --grow it may be able to force a reshape in the reverse direction.

Signed-off-by: NeilBrown <neilb@suse.de>

Create.c

@@ -65,7 +65,7 @@ int Create(struct supertype *st, char *mddev,
 	   char *name, int *uuid,
 	   int subdevs, struct mddev_dev *devlist,
 	   struct shape *s,
-	   struct context *c)
+	   struct context *c, unsigned long long data_offset)
 {
 	/*
 	 * Create a new raid array.
@@ -252,7 +252,7 @@ int Create(struct supertype *st, char *mddev,
 	newsize = s->size * 2;
 	if (st && ! st->ss->validate_geometry(st, s->level, s->layout, s->raiddisks,
 					      &s->chunk, s->size*2,
-					      INVALID_SECTORS, NULL,
+					      data_offset, NULL,
 					      &newsize, c->verbose>=0))
 		return 1;
 
@@ -335,7 +335,7 @@ int Create(struct supertype *st, char *mddev,
 				switch (st->ss->validate_geometry(
 						st, s->level, s->layout, s->raiddisks,
 						&s->chunk, s->size*2,
-						INVALID_SECTORS, dname,
+						data_offset, dname,
 						&freesize, c->verbose > 0)) {
 				case -1: /* Not valid, message printed, and not
 					  * worth checking any further */
@@ -372,7 +372,7 @@ int Create(struct supertype *st, char *mddev,
 			if (!st->ss->validate_geometry(st, s->level, s->layout,
 						       s->raiddisks,
 						       &s->chunk, s->size*2,
-						       INVALID_SECTORS,
+						       data_offset,
 						       dname, &freesize,
 						       c->verbose >= 0)) {
 
@@ -474,7 +474,7 @@ int Create(struct supertype *st, char *mddev,
 			if (!st->ss->validate_geometry(st, s->level, s->layout,
 						       s->raiddisks,
 						       &s->chunk, minsize*2,
-						       INVALID_SECTORS,
+						       data_offset,
 						       NULL, NULL, 0)) {
 				pr_err("devices too large for RAID level %d\n", s->level);
 				return 1;
@@ -682,7 +682,7 @@ int Create(struct supertype *st, char *mddev,
 		}
 	}
 	if (!st->ss->init_super(st, &info.array, s->size, name, c->homehost, uuid,
-				INVALID_SECTORS))
+				data_offset))
 		goto abort_locked;
 
 	total_slots = info.array.nr_disks;

Grow.c

@@ -1440,6 +1440,7 @@ static int reshape_container(char *container, char *devname,
 
 int Grow_reshape(char *devname, int fd,
 		 struct mddev_dev *devlist,
+		 unsigned long long data_offset,
 		 struct context *c, struct shape *s)
 {
 	/* Make some changes in the shape of an array.
@@ -1476,6 +1477,11 @@ int Grow_reshape(char *devname, int fd,
 	struct mdinfo info;
 	struct mdinfo *sra;
 
+	if (data_offset != INVALID_SECTORS) {
+		fprintf(stderr, Name ": --grow --data-offset not yet supported\n");
+		return 1;
+	}
+
 	if (ioctl(fd, GET_ARRAY_INFO, &array) < 0) {
 		pr_err("%s is not an active md array - aborting\n",
 			devname);

ReadMe.c

@@ -129,6 +129,7 @@ struct option long_options[] = {
     {"re-add",    0, 0,  ReAdd},
     {"homehost",  1, 0,  HomeHost},
     {"symlinks",  1, 0,  Symlinks},
+    {"data-offset",1, 0, DataOffset},
 
     /* For assemble */
     {"uuid",      1, 0, 'u'},
@@ -349,6 +350,8 @@ char Help_create[] =
 "  --raid-devices= -n : number of active devices in array\n"
 "  --spare-devices= -x: number of spare (eXtra) devices in initial array\n"
 "  --size=       -z   : Size (in K) of each drive in RAID1/4/5/6/10 - optional\n"
+"  --data-offset=     : Space to leave between start of device and start\n"
+"                     : of array data.\n"
 "  --force       -f   : Honour devices as listed on command line.  Don't\n"
 "                     : insert a missing drive for RAID5.\n"
 "  --run         -R   : insist of running the array even if not all\n"
@@ -545,6 +548,7 @@ char Help_grow[] =
 "                      : when changing parameters other than raid-devices\n"
 "  --array-size=  -Z   : Change visible size of array.  This does not change\n"
 "                      : any data on the device, and is not stable across restarts.\n"
+"  --data-offset=      : Location on device to move start of data to.\n"
 ;
 
 char Help_incr[] =

mdadm.8.in

@@ -767,6 +767,34 @@ or layout.  See the GROW MODE section below on RAID\-DEVICES CHANGES.
 The file must be stored on a separate device, not on the RAID array
 being reshaped.
 
+.TP
+.B \-\-data\-offset=
+Arrays with 1.x metadata can leave a gap between the start of the
+device and the start of array data.  This gap can be used for various
+metadata.  The start of data is known as the
+.IR data\-offset .
+Normally an appropriate data offset is computed automatically.
+However it can be useful to set it explicitly such as when re-creating
+an array which was originally created using a different version of
+.I mdadm
+which computed a different offset.
+
+Setting the offset explicitly over-rides the default.  The value given
+is in Kilobytes unless an 'M' or 'G' suffix is given.
+
+Since Linux 3.4,
+.B \-\-data\-offset
+can also be used with
+.B --grow
+for some RAID levels (initially on RAID10).  This allows the
+data-offset to be changed as part of the reshape process.  When the
+data offset is changed, no backup file is required as the difference
+in offsets is used to provide the same functionality.
+
+When the new offset is earlier than the old offset, the number of
+devices in the array cannot shrink.  When it is after the old offset,
+the number of devices in the array cannot increase.
+
 .TP
 .BR \-\-continue
 This option is complementary to the

mdadm.c

@@ -49,6 +49,7 @@ int main(int argc, char *argv[])
 	int i;
 
 	unsigned long long array_size = 0;
+	unsigned long long data_offset = INVALID_SECTORS;
 	struct mddev_ident ident;
 	char *configfile = NULL;
 	int devmode = 0;
@@ -457,6 +458,21 @@ int main(int argc, char *argv[])
 			}
 			continue;
 
+		case O(CREATE,DataOffset):
+		case O(GROW,DataOffset):
+			if (data_offset != INVALID_SECTORS) {
+				fprintf(stderr, Name ": data-offset may only be specified one. "
+					"Second value is %s.\n", optarg);
+				exit(2);
+			}
+			data_offset = parse_size(optarg);
+			if (data_offset == INVALID_SECTORS) {
+				fprintf(stderr, Name ": invalid data-offset: %s\n",
+					optarg);
+				exit(2);
+			}
+			continue;
+
 		case O(GROW,'l'):
 		case O(CREATE,'l'):
 		case O(BUILD,'l'): /* set raid level*/
@@ -1345,7 +1361,7 @@ int main(int argc, char *argv[])
 		rv = Create(ss, devlist->devname,
 			    ident.name, ident.uuid_set ? ident.uuid : NULL,
 			    devs_found-1, devlist->next,
-			    &s, &c);
+			    &s, &c, data_offset);
 		break;
 	case MISC:
 		if (devmode == 'E') {
@@ -1469,7 +1485,8 @@ int main(int argc, char *argv[])
 		else if (s.size > 0 || s.raiddisks || s.layout_str != NULL
 			 || s.chunk != 0 || s.level != UnSet) {
 			rv = Grow_reshape(devlist->devname, mdfd,
-					  devlist->next, &c, &s);
+					  devlist->next,
+					  data_offset, &c, &s);
 		} else if (array_size == 0)
 			pr_err("no changes to --grow\n");
 		break;

mdadm.h

@@ -326,6 +326,7 @@ enum special_options {
 	OffRootOpt,
 	Prefer,
 	KillOpt,
+	DataOffset,
 };
 
 enum prefix_standard {
@@ -1099,6 +1100,7 @@ extern int Grow_addbitmap(char *devname, int fd,
 			  struct context *c, struct shape *s);
 extern int Grow_reshape(char *devname, int fd,
 			struct mddev_dev *devlist,
+			unsigned long long data_offset,
 			struct context *c, struct shape *s);
 extern int Grow_restart(struct supertype *st, struct mdinfo *info,
 			int *fdlist, int cnt, char *backup_file, int verbose);
@@ -1127,7 +1129,8 @@ extern int Create(struct supertype *st, char *mddev,
 		  char *name, int *uuid,
 		  int subdevs, struct mddev_dev *devlist,
 		  struct shape *s,
-		  struct context *c);
+		  struct context *c,
+		  unsigned long long data_offset);
 
 extern int Detail(char *dev, struct context *c);
 extern int Detail_Platform(struct superswitch *ss, int scan, int verbose, int export, char *controller_path);