Increase raid456 stripe cache size if needed to --grow the array.

The setting used unfortunately requires intimate knowledge of the
kernel, and it not reset when the reshape finishes.

ChangeLog

@@ -12,6 +12,9 @@ Changes Prior to this release
 	get created automatically, as this is almost always what is wanted.
     -   Give useful message if raid4/5/6 cannot be started because it is
 	not clean and is also degraded.
+    -   Increase raid456 stripe cache size if needed to --grow the array.
+	The setting used unfortunately requires intimate knowledge of the
+	kernel, and it not reset when the reshape finishes.
 
 Changes Prior to 2.5.6 release
     -   Fix bug which meant "bitmap=xxx" in mdadm.conf was not handled

Grow.c

@@ -523,7 +523,7 @@ int Grow_reshape(char *devname, int fd, int quiet, char *backup_file,
 	case 6:
 		st = super_by_version(array.major_version,
 				      array.minor_version);
-		/* size can be changed independantly.
+		/* size can be changed independently.
 		 * layout/chunksize/raid_disks/level can be changed
 		 * though the kernel may not support it all.
 		 * If 'suspend_lo' is not present in devfs, then
@@ -620,7 +620,8 @@ int Grow_reshape(char *devname, int fd, int quiet, char *backup_file,
 		printf("mdadm: Need to backup %lluK of critical section..\n", last_block/2);
 
 		sra = sysfs_read(fd, 0,
-				 GET_COMPONENT|GET_DEVS|GET_OFFSET|GET_STATE);
+				 GET_COMPONENT|GET_DEVS|GET_OFFSET|GET_STATE|
+				 GET_CACHE);
 		if (!sra) {
 			fprintf(stderr, Name ": %s: Cannot get array details from sysfs\n",
 				devname);
@@ -742,10 +743,25 @@ int Grow_reshape(char *devname, int fd, int quiet, char *backup_file,
 		array.chunk_size = nchunk;
 		array.layout = nlayout;
 		if (ioctl(fd, SET_ARRAY_INFO, &array) != 0) {
+			if (errno == ENOSPC) {
+				/* stripe cache is not big enough.
+				 * It needs to be 4 times chunksize_size,
+				 * and we assume pagesize is 4K
+				 */
+				if (sra->cache_size < 4 * (nchunk/4096)) {
+					sysfs_set_num(sra, NULL,
+						      "stripe_cache_size",
+						      4 * (nchunk/4096) +1);
+					if (ioctl(fd, SET_ARRAY_INFO,
+						  &array) == 0)
+						goto ok;
+				}
+			}
 			fprintf(stderr, Name ": Cannot set device size/shape for %s: %s\n",
 				devname, strerror(errno));
 			goto abort;
 		}
+		ok: ;
 
 		/* suspend the relevant region */
 		sysfs_set_num(sra, NULL, "suspend_hi", 0); /* just in case */

mdadm.h

@@ -257,12 +257,14 @@ struct sysarray {
 	int	layout;
 	int	level;
 	int	spares;
+	int	cache_size;
 };
 /* various details can be requested */
 #define	GET_LEVEL	1
 #define	GET_LAYOUT	2
 #define	GET_COMPONENT	4
 #define	GET_CHUNK	8
+#define GET_CACHE	16
 
 #define	GET_DEVS	1024 /* gets role, major, minor */
 #define	GET_OFFSET	2048

sysfs.c

@@ -107,6 +107,12 @@ struct sysarray *sysfs_read(int fd, int devnum, unsigned long options)
 			goto abort;
 		sra->chunk = strtoul(buf, NULL, 0);
 	}
+	if (options & GET_CACHE) {
+		strcpy(base, "stripe_cache_size");
+		if (load_sys(fname, buf))
+			goto abort;
+		sra->cache_size = strtoul(buf, NULL, 0);
+	}
 
 	if (! (options & GET_DEVS))
 		return sra;