[PATCH] xfs: fix unaligned access in readdir

[PATCH] xfs: fix unaligned access in readdir

[Christoph Hellwig]

This patch should fix the issue seen on Alpha with unaligned accesses
in the new readdir code.   By aligning each dirent to sizeof(u64) we'll
avoid unaligned accesses.  To make doubly sure we're not hitting
problems also rearrange struct hack_dirent to avoid holes.


Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: linux-2.6-xfs/fs/xfs/linux-2.6/xfs_file.c
===================================================================
--- linux-2.6-xfs.orig/fs/xfs/linux-2.6/xfs_file.c	2007-12-26 15:35:33.000000000 +0100
+++ linux-2.6-xfs/fs/xfs/linux-2.6/xfs_file.c	2007-12-26 15:40:14.000000000 +0100
@@ -262,9 +262,9 @@ xfs_file_readdir(
 #else
 
 struct hack_dirent {
-	int		namlen;
-	loff_t		offset;
 	u64		ino;
+	loff_t		offset;
+	int		namlen;
 	unsigned int	d_type;
 	char		name[];
 };
@@ -286,8 +286,10 @@ xfs_hack_filldir(
 {
 	struct hack_callback *buf = __buf;
 	struct hack_dirent *de = (struct hack_dirent *)(buf->dirent + buf->used);
+	unsigned int reclen;
 
-	if (buf->used + sizeof(struct hack_dirent) + namlen > buf->len)
+	reclen = ALIGN(sizeof(struct hack_dirent) + namlen, sizeof(u64));
+	if (buf->used + reclen > buf->len)
 		return -EINVAL;
 
 	de->namlen = namlen;
@@ -295,7 +297,7 @@ xfs_hack_filldir(
 	de->ino = ino;
 	de->d_type = d_type;
 	memcpy(de->name, name, namlen);
-	buf->used += sizeof(struct hack_dirent) + namlen;
+	buf->used += reclen;
 	return 0;
 }
 
@@ -335,7 +337,8 @@ xfs_file_readdir(
 		offset = filp->f_pos;
 
 	while (!eof) {
-		int reclen;
+		unsigned int reclen;
+
 		start_offset = offset;
 
 		buf.used = 0;
@@ -356,7 +359,8 @@ xfs_file_readdir(
 				goto done;
 			}
 
-			reclen = sizeof(struct hack_dirent) + de->namlen;
+			reclen = ALIGN(sizeof(struct hack_dirent) + de->namlen,
+				       sizeof(u64));
 			size -= reclen;
 			de = (struct hack_dirent *)((char *)de + reclen);
 			curr_offset = de->offset /* & 0x7fffffff */;

Re: [PATCH] xfs: fix unaligned access in readdir

[Dustin Marquess]

This patch does indeed fix the problem.

Thanks!

-Dustin

Christoph Hellwig wrote:
> This patch should fix the issue seen on Alpha with unaligned accesses
> in the new readdir code.   By aligning each dirent to sizeof(u64) we'll
> avoid unaligned accesses.  To make doubly sure we're not hitting
> problems also rearrange struct hack_dirent to avoid holes.
> 
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> Index: linux-2.6-xfs/fs/xfs/linux-2.6/xfs_file.c
> ===================================================================
> --- linux-2.6-xfs.orig/fs/xfs/linux-2.6/xfs_file.c	2007-12-26 15:35:33.000000000 +0100
> +++ linux-2.6-xfs/fs/xfs/linux-2.6/xfs_file.c	2007-12-26 15:40:14.000000000 +0100
> @@ -262,9 +262,9 @@ xfs_file_readdir(
>  #else
>  
>  struct hack_dirent {
> -	int		namlen;
> -	loff_t		offset;
>  	u64		ino;
> +	loff_t		offset;
> +	int		namlen;
>  	unsigned int	d_type;
>  	char		name[];
>  };
> @@ -286,8 +286,10 @@ xfs_hack_filldir(
>  {
>  	struct hack_callback *buf = __buf;
>  	struct hack_dirent *de = (struct hack_dirent *)(buf->dirent + buf->used);
> +	unsigned int reclen;
>  
> -	if (buf->used + sizeof(struct hack_dirent) + namlen > buf->len)
> +	reclen = ALIGN(sizeof(struct hack_dirent) + namlen, sizeof(u64));
> +	if (buf->used + reclen > buf->len)
>  		return -EINVAL;
>  
>  	de->namlen = namlen;
> @@ -295,7 +297,7 @@ xfs_hack_filldir(
>  	de->ino = ino;
>  	de->d_type = d_type;
>  	memcpy(de->name, name, namlen);
> -	buf->used += sizeof(struct hack_dirent) + namlen;
> +	buf->used += reclen;
>  	return 0;
>  }
>  
> @@ -335,7 +337,8 @@ xfs_file_readdir(
>  		offset = filp->f_pos;
>  
>  	while (!eof) {
> -		int reclen;
> +		unsigned int reclen;
> +
>  		start_offset = offset;
>  
>  		buf.used = 0;
> @@ -356,7 +359,8 @@ xfs_file_readdir(
>  				goto done;
>  			}
>  
> -			reclen = sizeof(struct hack_dirent) + de->namlen;
> +			reclen = ALIGN(sizeof(struct hack_dirent) + de->namlen,
> +				       sizeof(u64));
>  			size -= reclen;
>  			de = (struct hack_dirent *)((char *)de + reclen);
>  			curr_offset = de->offset /* & 0x7fffffff */;
> 

Re: [PATCH] xfs: fix unaligned access in readdir

[Christoph Hellwig]

On Wed, Dec 26, 2007 at 04:48:57PM +0100, Christoph Hellwig wrote:
> This patch should fix the issue seen on Alpha with unaligned accesses
> in the new readdir code.   By aligning each dirent to sizeof(u64) we'll
> avoid unaligned accesses.  To make doubly sure we're not hitting
> problems also rearrange struct hack_dirent to avoid holes.

If anyone in Melbourne is getting back from Holidays it would be nice
if we could get this patch into 2.6.24-final still..