diff --git a/mdadm.h b/mdadm.h
index 79c47be..1f4f23b 100644
--- a/mdadm.h
+++ b/mdadm.h
@@ -206,6 +206,12 @@ struct mdinfo {
 						   * for native metadata it is
 						   * reshape_active field mirror
 						   */
+	/* During reshape we can sometimes change the data_offset to avoid
+	 * over-writing still-valid data.  We need to know if there is space.
+	 * So getinfo_super will fill in space_before and space_after in sectors.
+	 * data_offset can be increased or decreased by this amount.
+	 */
+	unsigned long long	space_before, space_after;
 	union {
 		unsigned long long resync_start; /* per-array resync position */
 		unsigned long long recovery_start; /* per-device rebuild position */
@@ -591,7 +597,7 @@ struct active_array;
 struct metadata_update;
 
 
-/* 'struct reshape' records the intermediate states
+/* 'struct reshape' records the intermediate states of
  * a general reshape.
  * The starting geometry is converted to the 'before' geometry
  * by at most an atomic level change. They could be the same.
diff --git a/super1.c b/super1.c
index 988ea17..444e6bb 100644
--- a/super1.c
+++ b/super1.c
@@ -665,10 +665,14 @@ static void uuid_from_super1(struct supertype *st, int uuid[4])
 static void getinfo_super1(struct supertype *st, struct mdinfo *info, char *map)
 {
 	struct mdp_superblock_1 *sb = st->sb;
+	struct bitmap_super_s *bsb = (void*)(((char*)sb)+MAX_SB_SIZE);
+	struct misc_dev_info *misc = (void*)(((char*)sb)+MAX_SB_SIZE+BM_SUPER_SIZE);
 	int working = 0;
 	unsigned int i;
 	unsigned int role;
 	unsigned int map_disks = info->array.raid_disks;
+	unsigned long long super_offset;
+	unsigned long long data_size;
 
 	memset(info, 0, sizeof(*info));
 	info->array.major_version = 1;
@@ -699,6 +703,39 @@ static void getinfo_super1(struct supertype *st, struct mdinfo *info, char *map)
 	else
 		role = __le16_to_cpu(sb->dev_roles[__le32_to_cpu(sb->dev_number)]);
 
+	super_offset = __le64_to_cpu(sb->super_offset);
+	data_size = __le64_to_cpu(sb->size);
+	if (info->data_offset < super_offset) {
+		unsigned long long end;
+		info->space_before = info->data_offset;
+		end = super_offset;
+		if (info->bitmap_offset < 0)
+			end += info->bitmap_offset;
+		if (info->data_offset + data_size < end)
+			info->space_after = end - data_size - info->data_offset;
+		else
+			info->space_after = 0;
+	} else {
+		info->space_before = (info->data_offset -
+				      super_offset);
+		if (info->bitmap_offset > 0) {
+			unsigned long long bmend = info->bitmap_offset;
+			unsigned long long size = __le64_to_cpu(bsb->sync_size);
+			size /= __le32_to_cpu(bsb->chunksize) >> 9;
+			size = (size + 7) >> 3;
+			size += sizeof(bitmap_super_t);
+			size = ROUND_UP(size, 4096);
+			size /= 512;
+			size += bmend;
+			if (size < info->space_before)
+				info->space_before -= size;
+			else
+				info->space_before = 0;
+		} else
+			info->space_before -= 8; /* superblock */
+		info->space_after = misc->device_size - data_size - info->data_offset;
+	}
+
 	info->disk.raid_disk = -1;
 	switch(role) {
 	case 0xFFFF: