Support --update=devicesize for cases where the underlying device can change size.

ChangeLog

@@ -6,6 +6,8 @@ Changes Prior to this release
 	missing devices (which is needed else if won't assemble.
 	Without this fix it would only assemble if one or zero
 	missing devices.
+    -   Support --update=devicesize for cases where the underlying device
+	can change size.
 
 Changes Prior to 2.5.6 release
     -   Fix bug which meant "bitmap=xxx" in mdadm.conf was not handled

mdadm.8

@@ -712,6 +712,7 @@ argument given to this flag can be one of
 .BR homehost ,
 .BR resync ,
 .BR byteorder ,
+.BR devicesize ,
 or
 .BR super-minor .
 
@@ -789,6 +790,22 @@ The
 option will correct the summaries in the superblock. That is the
 counts of total, working, active, failed, and spare devices.
 
+The
+.B devicesize
+will rarely be of use.  It applies to version 1.1 and 1.2 metadata
+only (where the metadata is at the start of the device) and is only
+useful when the component device has changed size (typically become
+larger).  The version 1 metadata records the amount of the device that
+can be used to store data, so if a device in a version 1.1 or 1.2
+array becomes larger, the metadata will still be visible, but the
+extra space will not.  In this case it might be useful to assemble the
+array with
+.BR --update=devicesize .
+This will cause
+.I mdadm
+to determine the maximum usable amount of space on each device and
+update the relevant field in the metadata.
+
 .TP
 .B --auto-update-homehost
 This flag is only meaning with auto-assembly (see discussion below).

mdadm.c

@@ -582,6 +582,8 @@ int main(int argc, char *argv[])
 				continue;
 			if (strcmp(update, "homehost")==0)
 				continue;
+			if (strcmp(update, "devicesize")==0)
+				continue;
 			if (strcmp(update, "byteorder")==0) {
 				if (ss) {
 					fprintf(stderr, Name ": must not set metadata type with --update=byteorder.\n");
@@ -601,8 +603,8 @@ int main(int argc, char *argv[])
 			else
 				fprintf(stderr, Name ": '--update=%s' is invalid.  ", update);
 			fprintf(stderr, "Valid --update options are:\n"
-				"     'sparc2.2', 'super-minor', 'uuid', 'name', 'resync',\n"
-				"     'summaries', 'homehost', 'byteorder'.\n");
+		"     'sparc2.2', 'super-minor', 'uuid', 'name', 'resync',\n"
+		"     'summaries', 'homehost', 'byteorder', 'devicesize'.\n");
 			exit(2);
 
 		case O(ASSEMBLE,NoDegraded): /* --no-degraded */

super1.c

@@ -94,6 +94,10 @@ struct mdp_superblock_1 {
 	__u16	dev_roles[0];	/* role in array, or 0xffff for a spare, or 0xfffe for faulty */
 };
 
+struct misc_dev_info {
+	__u64 device_size;
+};
+
 /* feature_map bits */
 #define MD_FEATURE_BITMAP_OFFSET	1
 #define	MD_FEATURE_RECOVERY_OFFSET	2 /* recovery_offset is present and
@@ -558,6 +562,17 @@ static int update_super1(struct mdinfo *info, void *sbv, char *update,
 		} else
 			strcpy(sb->set_name, info->name);
 	}
+	if (strcmp(update, "devicesize") == 0 &&
+	    __le64_to_cpu(sb->super_offset) <
+	    __le64_to_cpu(sb->data_offset)) {
+		/* set data_size to device size less data_offset */
+		struct misc_dev_info *misc = (struct misc_dev_info*)
+			(sbv + 1024 + sizeof(struct bitmap_super_s));
+		printf("Size was %llu\n", __le64_to_cpu(sb->data_size));
+		sb->data_size = __cpu_to_le64(
+			misc->device_size - __le64_to_cpu(sb->data_offset));
+		printf("Size is %llu\n", __le64_to_cpu(sb->data_size));
+	}
 	if (strcmp(update, "_reshape_progress")==0)
 		sb->reshape_position = __cpu_to_le64(info->reshape_progress);
 
@@ -568,7 +583,8 @@ static int update_super1(struct mdinfo *info, void *sbv, char *update,
 static int init_super1(struct supertype *st, void **sbp, mdu_array_info_t *info,
 		       unsigned long long size, char *name, char *homehost)
 {
-	struct mdp_superblock_1 *sb = malloc(1024 + sizeof(bitmap_super_t));
+	struct mdp_superblock_1 *sb = malloc(1024 + sizeof(bitmap_super_t) +
+					     sizeof(struct misc_dev_info));
 	int spares;
 	int rfd;
 	char defname[10];
@@ -882,8 +898,10 @@ static int compare_super1(void **firstp, void *secondv)
 		return 1;
 
 	if (!first) {
-		first = malloc(1024+sizeof(bitmap_super_t));
-		memcpy(first, second, 1024+sizeof(bitmap_super_t));
+		first = malloc(1024+sizeof(bitmap_super_t) +
+			       sizeof(struct misc_dev_info));
+		memcpy(first, second, 1024+sizeof(bitmap_super_t) +
+		       sizeof(struct misc_dev_info));
 		*firstp = first;
 		return 0;
 	}
@@ -908,6 +926,7 @@ static int load_super1(struct supertype *st, int fd, void **sbp, char *devname)
 	struct mdp_superblock_1 *super;
 	int uuid[4];
 	struct bitmap_super_s *bsb;
+	struct misc_dev_info *misc;
 
 
 	if (st->ss == NULL) {
@@ -997,7 +1016,8 @@ static int load_super1(struct supertype *st, int fd, void **sbp, char *devname)
 		return 1;
 	}
 
-	super = malloc(1024 + sizeof(bitmap_super_t));
+	super = malloc(1024 + sizeof(bitmap_super_t) +
+		       sizeof(struct misc_dev_info));
 
 	if (read(fd, super, 1024) != 1024) {
 		if (devname)
@@ -1031,6 +1051,11 @@ static int load_super1(struct supertype *st, int fd, void **sbp, char *devname)
 	}
 	*sbp = super;
 
+	bsb = (struct bitmap_super_s *)(((char*)super)+1024);
+
+	misc = (struct misc_dev_info*) (bsb+1);
+	misc->device_size = dsize;
+
 	/* Now check on the bitmap superblock */
 	if ((__le32_to_cpu(super->feature_map)&MD_FEATURE_BITMAP_OFFSET) == 0)
 		return 0;
@@ -1044,7 +1069,6 @@ static int load_super1(struct supertype *st, int fd, void **sbp, char *devname)
 		goto no_bitmap;
 
 	uuid_from_super1(uuid, super);
-	bsb = (struct bitmap_super_s *)(((char*)super)+1024);
 	if (__le32_to_cpu(bsb->magic) != BITMAP_MAGIC ||
 	    memcmp(bsb->uuid, uuid, 16) != 0)
 		goto no_bitmap;