dcache: allow word-at-a-time name hashing with big-endian CPUs
When explicitly hashing the end of a string with the word-at-a-time
interface, we have to be careful which end of the word we pick up.
On big-endian CPUs, the upper-bits will contain the data we're after, so
ensure we generate our masks accordingly (and avoid hashing whatever
random junk may have been sitting after the string).
This patch adds a new dcache helper, bytemask_from_count, which creates
a mask appropriate for the CPU endianness.
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/namei.c b/fs/namei.c
index c53d3a9..3531dee 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1598,11 +1598,6 @@
* do a "get_unaligned()" if this helps and is sufficiently
* fast.
*
- * - Little-endian machines (so that we can generate the mask
- * of low bytes efficiently). Again, we *could* do a byte
- * swapping load on big-endian architectures if that is not
- * expensive enough to make the optimization worthless.
- *
* - non-CONFIG_DEBUG_PAGEALLOC configurations (so that we
* do not trap on the (extremely unlikely) case of a page
* crossing operation.
@@ -1646,7 +1641,7 @@
if (!len)
goto done;
}
- mask = ~(~0ul << len*8);
+ mask = bytemask_from_count(len);
hash += mask & a;
done:
return fold_hash(hash);
