UBIFS: remove fast unmounting

This UBIFS feature has never worked properly, and it was a mistake
to add it because we simply have no use-cases. So, lets still accept
the fast_unmount mount option, but ignore it. This does not change
much, because UBIFS commit in sync_fs anyway, and sync_fs is called
while unmounting.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

Documentation/filesystems/ubifs.txt

@@ -79,13 +79,6 @@ Mount options
 
 (*) == default.
 
-norm_unmount (*)	commit on unmount; the journal is committed
-			when the file-system is unmounted so that the
-			next mount does not have to replay the journal
-			and it becomes very fast;
-fast_unmount		do not commit on unmount; this option makes
-			unmount faster, but the next mount slower
-			because of the need to replay the journal.
 bulk_read		read more in one go to take advantage of flash
 			media that read faster sequentially
 no_bulk_read (*)	do not bulk-read

fs/ubifs/super.c

@@ -957,13 +957,16 @@ static int ubifs_parse_options(struct ubifs_info *c, char *options,
 
 		token = match_token(p, tokens, args);
 		switch (token) {
+		/*
+		 * %Opt_fast_unmount and %Opt_norm_unmount options are ignored.
+		 * We accepte them in order to be backware-compatible. But this
+		 * should be removed at some point.
+		 */
 		case Opt_fast_unmount:
 			c->mount_opts.unmount_mode = 2;
-			c->fast_unmount = 1;
 			break;
 		case Opt_norm_unmount:
 			c->mount_opts.unmount_mode = 1;
-			c->fast_unmount = 0;
 			break;
 		case Opt_bulk_read:
 			c->mount_opts.bulk_read = 2;
@@ -1359,7 +1362,6 @@ static int mount_ubifs(struct ubifs_info *c)
 	       c->uuid[4], c->uuid[5], c->uuid[6], c->uuid[7],
 	       c->uuid[8], c->uuid[9], c->uuid[10], c->uuid[11],
 	       c->uuid[12], c->uuid[13], c->uuid[14], c->uuid[15]);
-	dbg_msg("fast unmount:        %d", c->fast_unmount);
 	dbg_msg("big_lpt              %d", c->big_lpt);
 	dbg_msg("log LEBs:            %d (%d - %d)",
 		c->log_lebs, UBIFS_LOG_LNUM, c->log_last);
@@ -1615,38 +1617,6 @@ out:
 	return err;
 }
 
-/**
- * commit_on_unmount - commit the journal when un-mounting.
- * @c: UBIFS file-system description object
- *
- * This function is called during un-mounting and re-mounting, and it commits
- * the journal unless the "fast unmount" mode is enabled.
- */
-static void commit_on_unmount(struct ubifs_info *c)
-{
-	long long bud_bytes;
-
-	if (!c->fast_unmount) {
-		dbg_gen("skip committing - fast unmount enabled");
-		return;
-	}
-
-	/*
-	 * This function is called before the background thread is stopped, so
-	 * we may race with ongoing commit, which means we have to take
-	 * @c->bud_lock to access @c->bud_bytes.
-	 */
-	spin_lock(&c->buds_lock);
-	bud_bytes = c->bud_bytes;
-	spin_unlock(&c->buds_lock);
-
-	if (bud_bytes) {
-		dbg_gen("run commit");
-		ubifs_run_commit(c);
-	} else
-		dbg_gen("journal is empty, do not run commit");
-}
-
 /**
  * ubifs_remount_ro - re-mount in read-only mode.
  * @c: UBIFS file-system description object
@@ -1661,7 +1631,6 @@ static void ubifs_remount_ro(struct ubifs_info *c)
 	ubifs_assert(!c->need_recovery);
 	ubifs_assert(!(c->vfs_sb->s_flags & MS_RDONLY));
 
-	commit_on_unmount(c);
 	mutex_lock(&c->umount_mutex);
 	if (c->bgt) {
 		kthread_stop(c->bgt);
@@ -2077,15 +2046,6 @@ out_close:
 
 static void ubifs_kill_sb(struct super_block *sb)
 {
-	struct ubifs_info *c = sb->s_fs_info;
-
-	/*
-	 * We do 'commit_on_unmount()' here instead of 'ubifs_put_super()'
-	 * in order to be outside BKL.
-	 */
-	if (sb->s_root && !(sb->s_flags & MS_RDONLY))
-		commit_on_unmount(c);
-	/* The un-mount routine is actually done in put_super() */
 	generic_shutdown_super(sb);
 }
 

fs/ubifs/ubifs.h

@@ -961,7 +961,6 @@ struct ubifs_debug_info;
  * @cs_lock: commit state lock
  * @cmt_wq: wait queue to sleep on if the log is full and a commit is running
  *
- * @fast_unmount: do not run journal commit before un-mounting
  * @big_lpt: flag that LPT is too big to write whole during commit
  * @no_chk_data_crc: do not check CRCs when reading data nodes (except during
  *                   recovery)
@@ -1202,7 +1201,6 @@ struct ubifs_info {
 	spinlock_t cs_lock;
 	wait_queue_head_t cmt_wq;
 
-	unsigned int fast_unmount:1;
 	unsigned int big_lpt:1;
 	unsigned int no_chk_data_crc:1;
 	unsigned int bulk_read:1;