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

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