reiserfs: locking, handle nested locks properly

The reiserfs write lock replaced the BKL and uses similar semantics.

Frederic's locking code makes a distinction between when the lock is nested
and when it's being acquired/released, but I don't think that's the right
distinction to make.

The right distinction is between the lock being released at end-of-use and
the lock being released for a schedule. The unlock should return the depth
and the lock should restore it, rather than the other way around as it is now.

This patch implements that and adds a number of places where the lock
should be dropped.
Signed-off-by: Jeff Mahoney <jeffm@suse.com>

fs/reiserfs/bitmap.c

@@ -1340,10 +1340,11 @@ struct buffer_head *reiserfs_read_bitmap_block(struct super_block *sb,
 		                 "reading failed", __func__, block);
 	else {
 		if (buffer_locked(bh)) {
+			int depth;
 			PROC_INFO_INC(sb, scan_bitmap.wait);
-			reiserfs_write_unlock(sb);
+			depth = reiserfs_write_unlock_nested(sb);
 			__wait_on_buffer(bh);
-			reiserfs_write_lock(sb);
+			reiserfs_write_lock_nested(sb, depth);
 		}
 		BUG_ON(!buffer_uptodate(bh));
 		BUG_ON(atomic_read(&bh->b_count) == 0);

fs/reiserfs/dir.c

@@ -71,6 +71,7 @@ int reiserfs_readdir_inode(struct inode *inode, struct dir_context *ctx)
 	char small_buf[32];	/* avoid kmalloc if we can */
 	struct reiserfs_dir_entry de;
 	int ret = 0;
+	int depth;
 
 	reiserfs_write_lock(inode->i_sb);
 
@@ -181,17 +182,17 @@ int reiserfs_readdir_inode(struct inode *inode, struct dir_context *ctx)
 				 * Since filldir might sleep, we can release
 				 * the write lock here for other waiters
 				 */
-				reiserfs_write_unlock(inode->i_sb);
+				depth = reiserfs_write_unlock_nested(inode->i_sb);
 				if (!dir_emit
 				    (ctx, local_buf, d_reclen, d_ino,
 				     DT_UNKNOWN)) {
-					reiserfs_write_lock(inode->i_sb);
+					reiserfs_write_lock_nested(inode->i_sb, depth);
 					if (local_buf != small_buf) {
 						kfree(local_buf);
 					}
 					goto end;
 				}
-				reiserfs_write_lock(inode->i_sb);
+				reiserfs_write_lock_nested(inode->i_sb, depth);
 				if (local_buf != small_buf) {
 					kfree(local_buf);
 				}

fs/reiserfs/fix_node.c

@@ -1022,9 +1022,9 @@ static int get_far_parent(struct tree_balance *tb,
 	if (buffer_locked(*pcom_father)) {
 
 		/* Release the write lock while the buffer is busy */
-		reiserfs_write_unlock(tb->tb_sb);
+		int depth = reiserfs_write_unlock_nested(tb->tb_sb);
 		__wait_on_buffer(*pcom_father);
-		reiserfs_write_lock(tb->tb_sb);
+		reiserfs_write_lock_nested(tb->tb_sb, depth);
 		if (FILESYSTEM_CHANGED_TB(tb)) {
 			brelse(*pcom_father);
 			return REPEAT_SEARCH;
@@ -1929,9 +1929,9 @@ static int get_direct_parent(struct tree_balance *tb, int h)
 		return REPEAT_SEARCH;
 
 	if (buffer_locked(bh)) {
-		reiserfs_write_unlock(tb->tb_sb);
+		int depth = reiserfs_write_unlock_nested(tb->tb_sb);
 		__wait_on_buffer(bh);
-		reiserfs_write_lock(tb->tb_sb);
+		reiserfs_write_lock_nested(tb->tb_sb, depth);
 		if (FILESYSTEM_CHANGED_TB(tb))
 			return REPEAT_SEARCH;
 	}
@@ -1952,6 +1952,7 @@ static int get_neighbors(struct tree_balance *tb, int h)
 	unsigned long son_number;
 	struct super_block *sb = tb->tb_sb;
 	struct buffer_head *bh;
+	int depth;
 
 	PROC_INFO_INC(sb, get_neighbors[h]);
 
@@ -1969,9 +1970,9 @@ static int get_neighbors(struct tree_balance *tb, int h)
 		     tb->FL[h]) ? tb->lkey[h] : B_NR_ITEMS(tb->
 								       FL[h]);
 		son_number = B_N_CHILD_NUM(tb->FL[h], child_position);
-		reiserfs_write_unlock(sb);
+		depth = reiserfs_write_unlock_nested(tb->tb_sb);
 		bh = sb_bread(sb, son_number);
-		reiserfs_write_lock(sb);
+		reiserfs_write_lock_nested(tb->tb_sb, depth);
 		if (!bh)
 			return IO_ERROR;
 		if (FILESYSTEM_CHANGED_TB(tb)) {
@@ -2009,9 +2010,9 @@ static int get_neighbors(struct tree_balance *tb, int h)
 		child_position =
 		    (bh == tb->FR[h]) ? tb->rkey[h] + 1 : 0;
 		son_number = B_N_CHILD_NUM(tb->FR[h], child_position);
-		reiserfs_write_unlock(sb);
+		depth = reiserfs_write_unlock_nested(tb->tb_sb);
 		bh = sb_bread(sb, son_number);
-		reiserfs_write_lock(sb);
+		reiserfs_write_lock_nested(tb->tb_sb, depth);
 		if (!bh)
 			return IO_ERROR;
 		if (FILESYSTEM_CHANGED_TB(tb)) {
@@ -2272,6 +2273,7 @@ static int wait_tb_buffers_until_unlocked(struct tree_balance *tb)
 		}
 
 		if (locked) {
+			int depth;
 #ifdef CONFIG_REISERFS_CHECK
 			repeat_counter++;
 			if ((repeat_counter % 10000) == 0) {
@@ -2286,9 +2288,9 @@ static int wait_tb_buffers_until_unlocked(struct tree_balance *tb)
 				    REPEAT_SEARCH : CARRY_ON;
 			}
 #endif
-			reiserfs_write_unlock(tb->tb_sb);
+			depth = reiserfs_write_unlock_nested(tb->tb_sb);
 			__wait_on_buffer(locked);
-			reiserfs_write_lock(tb->tb_sb);
+			reiserfs_write_lock_nested(tb->tb_sb, depth);
 			if (FILESYSTEM_CHANGED_TB(tb))
 				return REPEAT_SEARCH;
 		}
@@ -2359,9 +2361,9 @@ int fix_nodes(int op_mode, struct tree_balance *tb,
 
 	/* if it possible in indirect_to_direct conversion */
 	if (buffer_locked(tbS0)) {
-		reiserfs_write_unlock(tb->tb_sb);
+		int depth = reiserfs_write_unlock_nested(tb->tb_sb);
 		__wait_on_buffer(tbS0);
-		reiserfs_write_lock(tb->tb_sb);
+		reiserfs_write_lock_nested(tb->tb_sb, depth);
 		if (FILESYSTEM_CHANGED_TB(tb))
 			return REPEAT_SEARCH;
 	}

fs/reiserfs/ioctl.c

@@ -167,7 +167,6 @@ int reiserfs_commit_write(struct file *f, struct page *page,
 int reiserfs_unpack(struct inode *inode, struct file *filp)
 {
 	int retval = 0;
-	int depth;
 	int index;
 	struct page *page;
 	struct address_space *mapping;
@@ -183,11 +182,11 @@ int reiserfs_unpack(struct inode *inode, struct file *filp)
 		return 0;
 	}
 
-	depth = reiserfs_write_lock_once(inode->i_sb);
-
 	/* we need to make sure nobody is changing the file size beneath us */
 	reiserfs_mutex_lock_safe(&inode->i_mutex, inode->i_sb);
 
+	reiserfs_write_lock(inode->i_sb);
+
 	write_from = inode->i_size & (blocksize - 1);
 	/* if we are on a block boundary, we are already unpacked.  */
 	if (write_from == 0) {
@@ -221,6 +220,6 @@ int reiserfs_unpack(struct inode *inode, struct file *filp)
 
       out:
 	mutex_unlock(&inode->i_mutex);
-	reiserfs_write_unlock_once(inode->i_sb, depth);
+	reiserfs_write_unlock(inode->i_sb);
 	return retval;
 }

fs/reiserfs/lock.c

@@ -48,30 +48,35 @@ void reiserfs_write_unlock(struct super_block *s)
 	}
 }
 
-/*
- * If we already own the lock, just exit and don't increase the depth.
- * Useful when we don't want to lock more than once.
- *
- * We always return the lock_depth we had before calling
- * this function.
- */
-int reiserfs_write_lock_once(struct super_block *s)
+int __must_check reiserfs_write_unlock_nested(struct super_block *s)
 {
 	struct reiserfs_sb_info *sb_i = REISERFS_SB(s);
+	int depth;
 
-	if (sb_i->lock_owner != current) {
-		mutex_lock(&sb_i->lock);
-		sb_i->lock_owner = current;
-		return sb_i->lock_depth++;
-	}
+	/* this can happen when the lock isn't always held */
+	if (sb_i->lock_owner != current)
+		return -1;
+
+	depth = sb_i->lock_depth;
+
+	sb_i->lock_depth = -1;
+	sb_i->lock_owner = NULL;
+	mutex_unlock(&sb_i->lock);
 
-	return sb_i->lock_depth;
+	return depth;
 }
 
-void reiserfs_write_unlock_once(struct super_block *s, int lock_depth)
+void reiserfs_write_lock_nested(struct super_block *s, int depth)
 {
-	if (lock_depth == -1)
-		reiserfs_write_unlock(s);
+	struct reiserfs_sb_info *sb_i = REISERFS_SB(s);
+
+	/* this can happen when the lock isn't always held */
+	if (depth == -1)
+		return;
+
+	mutex_lock(&sb_i->lock);
+	sb_i->lock_owner = current;
+	sb_i->lock_depth = depth;
 }
 
 /*
@@ -82,9 +87,7 @@ void reiserfs_check_lock_depth(struct super_block *sb, char *caller)
 {
 	struct reiserfs_sb_info *sb_i = REISERFS_SB(sb);
 
-	if (sb_i->lock_depth < 0)
-		reiserfs_panic(sb, "%s called without kernel lock held %d",
-			       caller);
+	WARN_ON(sb_i->lock_depth < 0);
 }
 
 #ifdef CONFIG_REISERFS_CHECK

fs/reiserfs/namei.c

@@ -325,7 +325,6 @@ static struct dentry *reiserfs_lookup(struct inode *dir, struct dentry *dentry,
 				      unsigned int flags)
 {
 	int retval;
-	int lock_depth;
 	struct inode *inode = NULL;
 	struct reiserfs_dir_entry de;
 	INITIALIZE_PATH(path_to_entry);
@@ -333,12 +332,7 @@ static struct dentry *reiserfs_lookup(struct inode *dir, struct dentry *dentry,
 	if (REISERFS_MAX_NAME(dir->i_sb->s_blocksize) < dentry->d_name.len)
 		return ERR_PTR(-ENAMETOOLONG);
 
-	/*
-	 * Might be called with or without the write lock, must be careful
-	 * to not recursively hold it in case we want to release the lock
-	 * before rescheduling.
-	 */
-	lock_depth = reiserfs_write_lock_once(dir->i_sb);
+	reiserfs_write_lock(dir->i_sb);
 
 	de.de_gen_number_bit_string = NULL;
 	retval =
@@ -349,7 +343,7 @@ static struct dentry *reiserfs_lookup(struct inode *dir, struct dentry *dentry,
 		inode = reiserfs_iget(dir->i_sb,
 				      (struct cpu_key *)&(de.de_dir_id));
 		if (!inode || IS_ERR(inode)) {
-			reiserfs_write_unlock_once(dir->i_sb, lock_depth);
+			reiserfs_write_unlock(dir->i_sb);
 			return ERR_PTR(-EACCES);
 		}
 
@@ -358,7 +352,7 @@ static struct dentry *reiserfs_lookup(struct inode *dir, struct dentry *dentry,
 		if (IS_PRIVATE(dir))
 			inode->i_flags |= S_PRIVATE;
 	}
-	reiserfs_write_unlock_once(dir->i_sb, lock_depth);
+	reiserfs_write_unlock(dir->i_sb);
 	if (retval == IO_ERROR) {
 		return ERR_PTR(-EIO);
 	}
@@ -727,7 +721,6 @@ static int reiserfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode
 	struct inode *inode;
 	struct reiserfs_transaction_handle th;
 	struct reiserfs_security_handle security;
-	int lock_depth;
 	/* We need blocks for transaction + (user+group)*(quotas for new inode + update of quota for directory owner) */
 	int jbegin_count =
 	    JOURNAL_PER_BALANCE_CNT * 3 +
@@ -753,7 +746,7 @@ static int reiserfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode
 		return retval;
 	}
 	jbegin_count += retval;
-	lock_depth = reiserfs_write_lock_once(dir->i_sb);
+	reiserfs_write_lock(dir->i_sb);
 
 	retval = journal_begin(&th, dir->i_sb, jbegin_count);
 	if (retval) {
@@ -804,7 +797,7 @@ static int reiserfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode
 	d_instantiate(dentry, inode);
 	retval = journal_end(&th, dir->i_sb, jbegin_count);
 out_failed:
-	reiserfs_write_unlock_once(dir->i_sb, lock_depth);
+	reiserfs_write_unlock(dir->i_sb);
 	return retval;
 }
 
@@ -920,7 +913,6 @@ static int reiserfs_unlink(struct inode *dir, struct dentry *dentry)
 	struct reiserfs_transaction_handle th;
 	int jbegin_count;
 	unsigned long savelink;
-	int depth;
 
 	dquot_initialize(dir);
 
@@ -934,7 +926,7 @@ static int reiserfs_unlink(struct inode *dir, struct dentry *dentry)
 	    JOURNAL_PER_BALANCE_CNT * 2 + 2 +
 	    4 * REISERFS_QUOTA_TRANS_BLOCKS(dir->i_sb);
 
-	depth = reiserfs_write_lock_once(dir->i_sb);
+	reiserfs_write_lock(dir->i_sb);
 	retval = journal_begin(&th, dir->i_sb, jbegin_count);
 	if (retval)
 		goto out_unlink;
@@ -995,7 +987,7 @@ static int reiserfs_unlink(struct inode *dir, struct dentry *dentry)
 
 	retval = journal_end(&th, dir->i_sb, jbegin_count);
 	reiserfs_check_path(&path);
-	reiserfs_write_unlock_once(dir->i_sb, depth);
+	reiserfs_write_unlock(dir->i_sb);
 	return retval;
 
       end_unlink:
@@ -1005,7 +997,7 @@ static int reiserfs_unlink(struct inode *dir, struct dentry *dentry)
 	if (err)
 		retval = err;
       out_unlink:
-	reiserfs_write_unlock_once(dir->i_sb, depth);
+	reiserfs_write_unlock(dir->i_sb);
 	return retval;
 }
 

fs/reiserfs/prints.c

@@ -358,12 +358,13 @@ void __reiserfs_panic(struct super_block *sb, const char *id,
 	dump_stack();
 #endif
 	if (sb)
-		panic(KERN_WARNING "REISERFS panic (device %s): %s%s%s: %s\n",
+		printk(KERN_WARNING "REISERFS panic (device %s): %s%s%s: %s\n",
 		      sb->s_id, id ? id : "", id ? " " : "",
 		      function, error_buf);
 	else
-		panic(KERN_WARNING "REISERFS panic: %s%s%s: %s\n",
+		printk(KERN_WARNING "REISERFS panic: %s%s%s: %s\n",
 		      id ? id : "", id ? " " : "", function, error_buf);
+	BUG();
 }
 
 void __reiserfs_error(struct super_block *sb, const char *id,

fs/reiserfs/reiserfs.h

@@ -630,8 +630,8 @@ static inline int __reiserfs_is_journal_aborted(struct reiserfs_journal
  */
 void reiserfs_write_lock(struct super_block *s);
 void reiserfs_write_unlock(struct super_block *s);
-int reiserfs_write_lock_once(struct super_block *s);
-void reiserfs_write_unlock_once(struct super_block *s, int lock_depth);
+int __must_check reiserfs_write_unlock_nested(struct super_block *s);
+void reiserfs_write_lock_nested(struct super_block *s, int depth);
 
 #ifdef CONFIG_REISERFS_CHECK
 void reiserfs_lock_check_recursive(struct super_block *s);
@@ -667,31 +667,33 @@ static inline void reiserfs_lock_check_recursive(struct super_block *s) { }
  * - The inode mutex
  */
 static inline void reiserfs_mutex_lock_safe(struct mutex *m,
-			       struct super_block *s)
+					    struct super_block *s)
 {
-	reiserfs_lock_check_recursive(s);
-	reiserfs_write_unlock(s);
+	int depth;
+
+	depth = reiserfs_write_unlock_nested(s);
 	mutex_lock(m);
-	reiserfs_write_lock(s);
+	reiserfs_write_lock_nested(s, depth);
 }
 
 static inline void
 reiserfs_mutex_lock_nested_safe(struct mutex *m, unsigned int subclass,
-			       struct super_block *s)
+				struct super_block *s)
 {
-	reiserfs_lock_check_recursive(s);
-	reiserfs_write_unlock(s);
+	int depth;
+
+	depth = reiserfs_write_unlock_nested(s);
 	mutex_lock_nested(m, subclass);
-	reiserfs_write_lock(s);
+	reiserfs_write_lock_nested(s, depth);
 }
 
 static inline void
 reiserfs_down_read_safe(struct rw_semaphore *sem, struct super_block *s)
 {
-	reiserfs_lock_check_recursive(s);
-	reiserfs_write_unlock(s);
-	down_read(sem);
-	reiserfs_write_lock(s);
+       int depth;
+       depth = reiserfs_write_unlock_nested(s);
+       down_read(sem);
+       reiserfs_write_lock_nested(s, depth);
 }
 
 /*
@@ -701,9 +703,11 @@ reiserfs_down_read_safe(struct rw_semaphore *sem, struct super_block *s)
 static inline void reiserfs_cond_resched(struct super_block *s)
 {
 	if (need_resched()) {
-		reiserfs_write_unlock(s);
+		int depth;
+
+		depth = reiserfs_write_unlock_nested(s);
 		schedule();
-		reiserfs_write_lock(s);
+		reiserfs_write_lock_nested(s, depth);
 	}
 }
 

fs/reiserfs/resize.c

@@ -34,6 +34,7 @@ int reiserfs_resize(struct super_block *s, unsigned long block_count_new)
 	unsigned long int block_count, free_blocks;
 	int i;
 	int copy_size;
+	int depth;
 
 	sb = SB_DISK_SUPER_BLOCK(s);
 
@@ -43,7 +44,9 @@ int reiserfs_resize(struct super_block *s, unsigned long block_count_new)
 	}
 
 	/* check the device size */
+	depth = reiserfs_write_unlock_nested(s);
 	bh = sb_bread(s, block_count_new - 1);
+	reiserfs_write_lock_nested(s, depth);
 	if (!bh) {
 		printk("reiserfs_resize: can\'t read last block\n");
 		return -EINVAL;
@@ -125,9 +128,12 @@ int reiserfs_resize(struct super_block *s, unsigned long block_count_new)
 		 * transaction begins, and the new bitmaps don't matter if the
 		 * transaction fails. */
 		for (i = bmap_nr; i < bmap_nr_new; i++) {
+			int depth;
 			/* don't use read_bitmap_block since it will cache
 			 * the uninitialized bitmap */
+			depth = reiserfs_write_unlock_nested(s);
 			bh = sb_bread(s, i * s->s_blocksize * 8);
+			reiserfs_write_lock_nested(s, depth);
 			if (!bh) {
 				vfree(bitmap);
 				return -EIO;
@@ -138,9 +144,9 @@ int reiserfs_resize(struct super_block *s, unsigned long block_count_new)
 
 			set_buffer_uptodate(bh);
 			mark_buffer_dirty(bh);
-			reiserfs_write_unlock(s);
+			depth = reiserfs_write_unlock_nested(s);
 			sync_dirty_buffer(bh);
-			reiserfs_write_lock(s);
+			reiserfs_write_lock_nested(s, depth);
 			// update bitmap_info stuff
 			bitmap[i].free_count = sb_blocksize(sb) * 8 - 1;
 			brelse(bh);

fs/reiserfs/stree.c

@@ -524,14 +524,14 @@ static int is_tree_node(struct buffer_head *bh, int level)
  * the caller (search_by_key) will perform other schedule-unsafe
  * operations just after calling this function.
  *
- * @return true if we have unlocked
+ * @return depth of lock to be restored after read completes
  */
-static bool search_by_key_reada(struct super_block *s,
+static int search_by_key_reada(struct super_block *s,
 				struct buffer_head **bh,
 				b_blocknr_t *b, int num)
 {
 	int i, j;
-	bool unlocked = false;
+	int depth = -1;
 
 	for (i = 0; i < num; i++) {
 		bh[i] = sb_getblk(s, b[i]);
@@ -549,15 +549,13 @@ static bool search_by_key_reada(struct super_block *s,
 		 * you have to make sure the prepared bit isn't set on this buffer
 		 */
 		if (!buffer_uptodate(bh[j])) {
-			if (!unlocked) {
-				reiserfs_write_unlock(s);
-				unlocked = true;
-			}
+			if (depth == -1)
+				depth = reiserfs_write_unlock_nested(s);
 			ll_rw_block(READA, 1, bh + j);
 		}
 		brelse(bh[j]);
 	}
-	return unlocked;
+	return depth;
 }
 
 /**************************************************************************
@@ -645,26 +643,26 @@ int search_by_key(struct super_block *sb, const struct cpu_key *key,	/* Key to s
 		   have a pointer to it. */
 		if ((bh = last_element->pe_buffer =
 		     sb_getblk(sb, block_number))) {
-			bool unlocked = false;
 
-			if (!buffer_uptodate(bh) && reada_count > 1)
-				/* may unlock the write lock */
-				unlocked = search_by_key_reada(sb, reada_bh,
-						    reada_blocks, reada_count);
 			/*
-			 * If we haven't already unlocked the write lock,
-			 * then we need to do that here before reading
-			 * the current block
+			 * We'll need to drop the lock if we encounter any
+			 * buffers that need to be read. If all of them are
+			 * already up to date, we don't need to drop the lock.
 			 */
-			if (!buffer_uptodate(bh) && !unlocked) {
-				reiserfs_write_unlock(sb);
-				unlocked = true;
-			}
+			int depth = -1;
+
+			if (!buffer_uptodate(bh) && reada_count > 1)
+				depth = search_by_key_reada(sb, reada_bh,
+						    reada_blocks, reada_count);
+
+			if (!buffer_uptodate(bh) && depth == -1)
+				depth = reiserfs_write_unlock_nested(sb);
+
 			ll_rw_block(READ, 1, &bh);
 			wait_on_buffer(bh);
 
-			if (unlocked)
-				reiserfs_write_lock(sb);
+			if (depth != -1)
+				reiserfs_write_lock_nested(sb, depth);
 			if (!buffer_uptodate(bh))
 				goto io_error;
 		} else {
@@ -1059,9 +1057,7 @@ static char prepare_for_delete_or_cut(struct reiserfs_transaction_handle *th, st
 			reiserfs_free_block(th, inode, block, 1);
 		    }
 
-		    reiserfs_write_unlock(sb);
-		    cond_resched();
-		    reiserfs_write_lock(sb);
+		    reiserfs_cond_resched(sb);
 
 		    if (item_moved (&s_ih, path))  {
 			need_re_search = 1;

fs/reiserfs/super.c

@@ -624,7 +624,6 @@ static void reiserfs_dirty_inode(struct inode *inode, int flags)
 	struct reiserfs_transaction_handle th;
 
 	int err = 0;
-	int lock_depth;
 
 	if (inode->i_sb->s_flags & MS_RDONLY) {
 		reiserfs_warning(inode->i_sb, "clm-6006",
@@ -632,7 +631,7 @@ static void reiserfs_dirty_inode(struct inode *inode, int flags)
 				 inode->i_ino);
 		return;
 	}
-	lock_depth = reiserfs_write_lock_once(inode->i_sb);
+	reiserfs_write_lock(inode->i_sb);
 
 	/* this is really only used for atime updates, so they don't have
 	 ** to be included in O_SYNC or fsync
@@ -645,7 +644,7 @@ static void reiserfs_dirty_inode(struct inode *inode, int flags)
 	journal_end(&th, inode->i_sb, 1);
 
 out:
-	reiserfs_write_unlock_once(inode->i_sb, lock_depth);
+	reiserfs_write_unlock(inode->i_sb);
 }
 
 static int reiserfs_show_options(struct seq_file *seq, struct dentry *root)