[PATCH] reiserfs: Add comment to explain endianness issue in xattr_hash

[PATCH] reiserfs: Add comment to explain endianness issue in xattr_hash

[Bharath Vedartham]

csum_partial() gives different results for little-endian and big-endian
hosts. This causes images created on little-endian hosts and mounted on
big endian hosts to see csum mismatches. This causes an endianness bug.
Sparse gives a warning as csum_partial returns a restricted integer type
__wsum_t and xattr_hash expects __u32. This warning acts as a reminder
for this bug and should not be suppressed.

This comment aims to convey these endianness issues.

Signed-off-by: Bharath Vedartham <linux.bhar@gmail.com>
---
 fs/reiserfs/xattr.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/reiserfs/xattr.c b/fs/reiserfs/xattr.c
index 32d8986..0ea6654 100644
--- a/fs/reiserfs/xattr.c
+++ b/fs/reiserfs/xattr.c
@@ -450,6 +450,16 @@ static struct page *reiserfs_get_page(struct inode *dir, size_t n)
 
 static inline __u32 xattr_hash(const char *msg, int len)
 {
+	/*
+	 * csum_partial() gives different results for little-endian and
+	 * big endian hosts. Images created on little-endian hosts and
+	 * mounted on big-endian hosts(and vice versa) will see csum mismatches
+	 * when trying to fetch xattrs. Treating the hash as __wsum_t would
+	 * lower the frequency of mismatch. This is an endianness bug in reiserfs.
+	 * The return statement would result in a sparse warning. Do not fix the sparse
+	 * warning so as to not hide the reminder of the bug.
+	 */
+
 	return csum_partial(msg, len, 0);
 }
 
-- 
2.7.4

Re: [PATCH] reiserfs: Add comment to explain endianness issue in xattr_hash

[Bharath Vedartham]

On Tue, Apr 23, 2019 at 09:48:31PM +0530, Bharath Vedartham wrote:
> csum_partial() gives different results for little-endian and big-endian
> hosts. This causes images created on little-endian hosts and mounted on
> big endian hosts to see csum mismatches. This causes an endianness bug.
> Sparse gives a warning as csum_partial returns a restricted integer type
> __wsum_t and xattr_hash expects __u32. This warning acts as a reminder
> for this bug and should not be suppressed.
> 
> This comment aims to convey these endianness issues.
> 
> Signed-off-by: Bharath Vedartham <linux.bhar@gmail.com>
> ---
>  fs/reiserfs/xattr.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/fs/reiserfs/xattr.c b/fs/reiserfs/xattr.c
> index 32d8986..0ea6654 100644
> --- a/fs/reiserfs/xattr.c
> +++ b/fs/reiserfs/xattr.c
> @@ -450,6 +450,16 @@ static struct page *reiserfs_get_page(struct inode *dir, size_t n)
>  
>  static inline __u32 xattr_hash(const char *msg, int len)
>  {
> +	/*
> +	 * csum_partial() gives different results for little-endian and
> +	 * big endian hosts. Images created on little-endian hosts and
> +	 * mounted on big-endian hosts(and vice versa) will see csum mismatches
> +	 * when trying to fetch xattrs. Treating the hash as __wsum_t would
> +	 * lower the frequency of mismatch. This is an endianness bug in reiserfs.
> +	 * The return statement would result in a sparse warning. Do not fix the sparse
> +	 * warning so as to not hide the reminder of the bug.
> +	 */
> +
>  	return csum_partial(msg, len, 0);
>  }
>  
> -- 
> 2.7.4
>

Is this good or is it lacking any explanation?