From cad3f00763dcf9dfc62cbddf4bd714ab5a71a0eb Mon Sep 17 00:00:00 2001
From: Theodore Ts'o
Date: Sun, 19 Dec 2010 22:07:02 -0500
Subject: ext4: optimize ext4_check_dir_entry() with unlikely() annotations

This function gets called a lot for large directories, and the answer
is almost always "no, no, there's no problem".  This means using
unlikely() is a good thing.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---
 fs/ext4/dir.c | 40 +++++++++++++++++++++++-----------------
 1 file changed, 23 insertions(+), 17 deletions(-)

(limited to 'fs/ext4/dir.c')

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index ece76fb6a40c..bd5d74d06399 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -60,7 +60,11 @@ static unsigned char get_dtype(struct super_block *sb, int filetype)
 	return (ext4_filetype_table[filetype]);
 }
 
-
+/*
+ * Return 0 if the directory entry is OK, and 1 if there is a problem
+ *
+ * Note: this is the opposite of what ext2 and ext3 historically returned...
+ */
 int __ext4_check_dir_entry(const char *function, unsigned int line,
 			   struct inode *dir,
 			   struct ext4_dir_entry_2 *de,
@@ -71,26 +75,28 @@ int __ext4_check_dir_entry(const char *function, unsigned int line,
 	const int rlen = ext4_rec_len_from_disk(de->rec_len,
 						dir->i_sb->s_blocksize);
 
-	if (rlen < EXT4_DIR_REC_LEN(1))
+	if (unlikely(rlen < EXT4_DIR_REC_LEN(1)))
 		error_msg = "rec_len is smaller than minimal";
-	else if (rlen % 4 != 0)
+	else if (unlikely(rlen % 4 != 0))
 		error_msg = "rec_len % 4 != 0";
-	else if (rlen < EXT4_DIR_REC_LEN(de->name_len))
+	else if (unlikely(rlen < EXT4_DIR_REC_LEN(de->name_len)))
 		error_msg = "rec_len is too small for name_len";
-	else if (((char *) de - bh->b_data) + rlen > dir->i_sb->s_blocksize)
+	else if (unlikely(((char *) de - bh->b_data) + rlen >
+			  dir->i_sb->s_blocksize))
 		error_msg = "directory entry across blocks";
-	else if (le32_to_cpu(de->inode) >
-			le32_to_cpu(EXT4_SB(dir->i_sb)->s_es->s_inodes_count))
+	else if (unlikely(le32_to_cpu(de->inode) >
+			le32_to_cpu(EXT4_SB(dir->i_sb)->s_es->s_inodes_count)))
 		error_msg = "inode out of bounds";
+	else
+		return 0;
 
-	if (error_msg != NULL)
-		ext4_error_inode(dir, function, line, bh->b_blocknr,
-			"bad entry in directory: %s - "
-			"offset=%u(%u), inode=%u, rec_len=%d, name_len=%d",
-			error_msg, (unsigned) (offset%bh->b_size), offset,
-			le32_to_cpu(de->inode),
-			rlen, de->name_len);
-	return error_msg == NULL ? 1 : 0;
+	ext4_error_inode(dir, function, line, bh->b_blocknr,
+			 "bad entry in directory: %s - "
+			 "offset=%u(%u), inode=%u, rec_len=%d, name_len=%d",
+			 error_msg, (unsigned) (offset%bh->b_size), offset,
+			 le32_to_cpu(de->inode),
+			 rlen, de->name_len);
+	return 1;
 }
 
 static int ext4_readdir(struct file *filp,
@@ -194,8 +200,8 @@ revalidate:
 		while (!error && filp->f_pos < inode->i_size
 		       && offset < sb->s_blocksize) {
 			de = (struct ext4_dir_entry_2 *) (bh->b_data + offset);
-			if (!ext4_check_dir_entry(inode, de,
-						  bh, offset)) {
+			if (ext4_check_dir_entry(inode, de,
+						 bh, offset)) {
 				/*
 				 * On error, skip the f_pos to the next block
 				 */
-- 
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