From: NeilBrown <neilb@suse.de>

Allow a whole 'side' of a RAID10 to be failed at once.
This is useful if separate code detects that the path to one
set of devices have disappeared.
The naming of sides match the "set-A", "set-B" etc reported by
"mdadm --detail".
So
  mdadm /dev/md0 --fail set-A

will remove half of the devices on a typical RAID10

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

---
 Manage.c |   53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

--- mdadm-3.2.6.orig/Manage.c
+++ mdadm-3.2.6/Manage.c
@@ -550,6 +550,59 @@ int Manage_subdevs(char *devname, int fd
 				next = dv;
 			if (stat(add_dev, &stb) < 0)
 				continue;
+		} else if (strncmp(dv->devname, "set-", 4) == 0) {
+			int copies, set;
+			char setname[10];
+			int remaining_disks = array.nr_disks;
+
+			if (dv->disposition != 'r' &&
+			    dv->disposition != 'f') {
+				fprintf(stderr, Name ": %s only meaningful "
+					"with -r or -f\n", dv->devname);
+				goto abort;
+			}
+			if (array.level != 10) {
+				fprintf(stderr, Name ": %s only meaningful "
+					"with RAID10 arrays\n", dv->devname);
+				goto abort;
+			}
+			copies = ((array.layout & 0xff) *
+				  ((array.layout >> 8) & 0xff));
+			if (array.raid_disks % copies != 0 ||
+			    copies > 26) {
+				fprintf(stderr, Name ": %s not meaningful "
+					"with this array\n", dv->devname);
+				goto abort;
+			}
+			for (;j < MAX_DISKS && remaining_disks > 0; j++) {
+				unsigned dev;
+				disc.number = j;
+				if (ioctl(fd, GET_DISK_INFO, &disc))
+					continue;
+				if (disc.major == 0 && disc.minor == 0)
+					continue;
+				remaining_disks --;
+				if ((disc.state & 1) == 1) /* faulty */
+					continue;
+				set = disc.raid_disk % copies;
+				sprintf(setname, "set-%c", set + 'A');
+				if (strcmp(setname, dv->devname) != 0)
+					continue;
+				dev = makedev(disc.major, disc.minor);
+				if (stb.st_rdev == dev)
+					/* already did that one */
+					continue;
+				stb.st_rdev = dev;
+				next = dv;
+				/* same slot again next time - things might
+				 * have reshuffled */
+				jnext = j;
+				sprintf(dvname,"%d:%d", disc.major, disc.minor);
+				dnprintable = dvname;
+				break;
+			}
+			if (next != dv)
+				continue;
 		} else if (strchr(dv->devname, '/') == NULL &&
 			   strchr(dv->devname, ':') == NULL &&
 			   strlen(dv->devname) < 50) {