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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>
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@ -192,7 +192,7 @@ static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char
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if (!tcount)
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return 0;
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}
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mask = ~(~0ul << tcount*8);
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mask = bytemask_from_count(tcount);
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return unlikely(!!((a ^ b) & mask));
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}
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@ -1598,11 +1598,6 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd)
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* do a "get_unaligned()" if this helps and is sufficiently
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* fast.
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*
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* - Little-endian machines (so that we can generate the mask
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* of low bytes efficiently). Again, we *could* do a byte
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* swapping load on big-endian architectures if that is not
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* expensive enough to make the optimization worthless.
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*
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* - non-CONFIG_DEBUG_PAGEALLOC configurations (so that we
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* do not trap on the (extremely unlikely) case of a page
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* crossing operation.
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@ -1646,7 +1641,7 @@ unsigned int full_name_hash(const unsigned char *name, unsigned int len)
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if (!len)
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goto done;
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}
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mask = ~(~0ul << len*8);
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mask = bytemask_from_count(len);
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hash += mask & a;
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done:
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return fold_hash(hash);
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@ -29,8 +29,10 @@ struct vfsmount;
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/* The hash is always the low bits of hash_len */
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#ifdef __LITTLE_ENDIAN
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#define HASH_LEN_DECLARE u32 hash; u32 len;
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#define bytemask_from_count(cnt) (~(~0ul << (cnt)*8))
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#else
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#define HASH_LEN_DECLARE u32 len; u32 hash;
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#define bytemask_from_count(cnt) (~(~0ul >> (cnt)*8))
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#endif
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/*
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