nilfs2: clean up sketch file

The sketch file is a file to mark checkpoints with user data.  It was
experimentally introduced in the original implementation, and now
obsolete.  The file was handled differently with regular files; the file
size got truncated when a checkpoint was created.

This stops the special treatment and will treat it as a regular file.
Most users are not affected because mkfs.nilfs2 no longer makes this file.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/nilfs2/segment.h

@@ -108,7 +108,6 @@ struct nilfs_segsum_pointer {
  * @sc_nblk_this_inc: Number of blocks included in the current logical segment
  * @sc_seg_ctime: Creation time
  * @sc_flags: Internal flags
- * @sc_sketch_inode: Inode of the sketch file
  * @sc_state_lock: spinlock for sc_state and so on
  * @sc_state: Segctord state flags
  * @sc_flush_request: inode bitmap of metadata files to be flushed
@@ -158,13 +157,6 @@ struct nilfs_sc_info {
 
 	unsigned long		sc_flags;
 
-	/*
-	 * Pointer to an inode of the sketch.
-	 * This pointer is kept only while it contains data.
-	 * We protect it with a semaphore of the segment constructor.
-	 */
-	struct inode	       *sc_sketch_inode;
-
 	spinlock_t		sc_state_lock;
 	unsigned long		sc_state;
 	unsigned long		sc_flush_request;