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