Btrfs-progs: remove unused variable and update btrfs-image man page

Remove unused variable in btrfs-image.c (update_super) and update man page documentation about -r option. Running btrfsck on a restored image produces missing chunk information. This is because by default, btrfs-image fixes up chunk tree to use 1 stripe pointing to the primary device. This in turns results in btrfsck making some noise.

$  ./mkfs.btrfs /dev/sdb2 -f
$  ./btrfs-image /dev/sdb2 btrfs_image_output
$  ./btrfs-image -r btrfs_image_output disk-image
$  ./btrfsck disk-image

Device extent[1, 29360128, 8388608] didn't find the relative chunk. Device extent[1, 1111490560, 1073741824] didn't find the relative chunk.

Ideally btfsck should be updated to reflect this default behavior and not through these messages, but it isn't harmful and can be done later.

---
 btrfs-image.c        | 3 ---
 man/btrfs-image.8.in | 5 ++++-
 2 files changed, 4 insertions(+), 4 deletions(-)

index c3a7fe5..cc8627c 100644
@@ -1373,7 +1373,6 @@ static int update_super(u8 *buffer)
 	u32 new_array_size = 0;
 	u32 array_size;
 	u32 cur = 0;
-	u32 new_cur = 0;
 	u8 *ptr, *write_ptr;
 	int old_num_stripes;
 

@@ -1390,7 +1389,6 @@ static int update_super(u8 *buffer)
 		write_ptr += sizeof(*disk_key);
 		ptr += sizeof(*disk_key);
 		cur += sizeof(*disk_key);
-		new_cur += sizeof(*disk_key);
 
 		if (key.type == BTRFS_CHUNK_ITEM_KEY) {
 			chunk = (struct btrfs_chunk *)ptr;

@@ -1406,7 +1404,6 @@ static int update_super(u8 *buffer)
 			memcpy(chunk->stripe.dev_uuid, super->dev_item.uuid,
 			       BTRFS_UUID_SIZE);
 			new_array_size += sizeof(*chunk);
-			new_cur += sizeof(*chunk);
 		} else {
 			fprintf(stderr, "Bogus key in the sys chunk array "
 				"%d\n", key.type);

index d5ba594..3f51f3f 100644
@@ -17,7 +17,10 @@ is the image file that btrfs-image creates. When used with \fB-r\fP option,
 .SH OPTIONS
 .TP
 \fB\-r\fP
-restore metadump image.
+Restore metadump image. By default, this fixes super's chunk tree, by
+using 1 stripe pointing to primary device, so that file system can be
+restored by running tree log reply if possible. To restore without
+changing number of stripes in chunk tree check \fB-o\fP option.
 .TP
 \fB\-c\fR \fIvalue\fP
 compression level (0 ~ 9).

1.8.5.3