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

@@ -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 @@ static int ext4_readdir(struct file *filp,
 		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
 				 */

fs/ext4/ext4.h

@@ -1639,7 +1639,8 @@ extern int __ext4_check_dir_entry(const char *, unsigned int, struct inode *,
 				  struct ext4_dir_entry_2 *,
 				  struct buffer_head *, unsigned int);
 #define ext4_check_dir_entry(dir, de, bh, offset) \
-	__ext4_check_dir_entry(__func__, __LINE__, (dir), (de), (bh), (offset))
+	unlikely(__ext4_check_dir_entry(__func__, __LINE__, (dir), (de), \
+					(bh), (offset)))
 extern int ext4_htree_store_dirent(struct file *dir_file, __u32 hash,
 				    __u32 minor_hash,
 				    struct ext4_dir_entry_2 *dirent);

fs/ext4/namei.c

@@ -581,9 +581,9 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 					   dir->i_sb->s_blocksize -
 					   EXT4_DIR_REC_LEN(0));
 	for (; de < top; de = ext4_next_entry(de, dir->i_sb->s_blocksize)) {
-		if (!ext4_check_dir_entry(dir, de, bh,
-					(block<<EXT4_BLOCK_SIZE_BITS(dir->i_sb))
-						+((char *)de - bh->b_data))) {
+		if (ext4_check_dir_entry(dir, de, bh,
+				(block<<EXT4_BLOCK_SIZE_BITS(dir->i_sb))
+					 + ((char *)de - bh->b_data))) {
 			/* On error, skip the f_pos to the next block. */
 			dir_file->f_pos = (dir_file->f_pos |
 					(dir->i_sb->s_blocksize - 1)) + 1;
@@ -820,7 +820,7 @@ static inline int search_dirblock(struct buffer_head *bh,
 		if ((char *) de + namelen <= dlimit &&
 		    ext4_match (namelen, name, de)) {
 			/* found a match - just to be sure, do a full check */
-			if (!ext4_check_dir_entry(dir, de, bh, offset))
+			if (ext4_check_dir_entry(dir, de, bh, offset))
 				return -1;
 			*res_dir = de;
 			return 1;
@@ -1269,7 +1269,7 @@ static int add_dirent_to_buf(handle_t *handle, struct dentry *dentry,
 		de = (struct ext4_dir_entry_2 *)bh->b_data;
 		top = bh->b_data + blocksize - reclen;
 		while ((char *) de <= top) {
-			if (!ext4_check_dir_entry(dir, de, bh, offset))
+			if (ext4_check_dir_entry(dir, de, bh, offset))
 				return -EIO;
 			if (ext4_match(namelen, name, de))
 				return -EEXIST;
@@ -1636,7 +1636,7 @@ static int ext4_delete_entry(handle_t *handle,
 	pde = NULL;
 	de = (struct ext4_dir_entry_2 *) bh->b_data;
 	while (i < bh->b_size) {
-		if (!ext4_check_dir_entry(dir, de, bh, i))
+		if (ext4_check_dir_entry(dir, de, bh, i))
 			return -EIO;
 		if (de == de_del)  {
 			BUFFER_TRACE(bh, "get_write_access");
@@ -1919,7 +1919,7 @@ static int empty_dir(struct inode *inode)
 			}
 			de = (struct ext4_dir_entry_2 *) bh->b_data;
 		}
-		if (!ext4_check_dir_entry(inode, de, bh, offset)) {
+		if (ext4_check_dir_entry(inode, de, bh, offset)) {
 			de = (struct ext4_dir_entry_2 *)(bh->b_data +
 							 sb->s_blocksize);
 			offset = (offset | (sb->s_blocksize - 1)) + 1;