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Date: Sat, 28 May 2016 15:57:15 -0400
From: George Spelvin <linux@...encehorizons.net>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
lkml <linux-kernel@...r.kernel.org>
Cc: "J . Bruce Fields" <bfields@...hat.com>,
George Spelvin <linux@...encehorizons.net>
Subject: [PATCH v3 02/10] fs/namei.c: Add hashlen_string() function
We'd like to make more use of the highly-optimized dcache hash functions
throughout the kernel, rather than have every subsystem create its own,
and a function that hashes basic null-terminated strings is required
for that.
(The name is to emphasize that it returns both hash and length.)
It's actually useful in the dcache itself, specifically d_alloc_name().
Other uses in the next patch.
full_name_hash() is also tweaked to make it more generally useful:
1) Take a "char *" rather than "unsigned char *" argument, to
be consistent with hash_name().
2) Handle zero-length inputs. If we want more callers, we don't want
to make them worry about corner cases.
Signed-off-by: George Spelvin <linux@...encehorizons.net>
---
fs/dcache.c | 3 +--
fs/namei.c | 51 +++++++++++++++++++++++++++++++++++++++++-----
include/linux/stringhash.h | 8 ++++++--
3 files changed, 53 insertions(+), 9 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index d5ecc6e4..19b75180 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1653,8 +1653,7 @@ struct dentry *d_alloc_name(struct dentry *parent, const char *name)
struct qstr q;
q.name = name;
- q.len = strlen(name);
- q.hash = full_name_hash(q.name, q.len);
+ q.hash_len = hashlen_string(name);
return d_alloc(parent, &q);
}
EXPORT_SYMBOL(d_alloc_name);
diff --git a/fs/namei.c b/fs/namei.c
index 42f8ca03..dd98d43a 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1822,19 +1822,20 @@ static inline unsigned long mix_hash(unsigned long hash)
#endif
-unsigned int full_name_hash(const unsigned char *name, unsigned int len)
+/* Return the hash of a string of known length */
+unsigned int full_name_hash(const char *name, unsigned int len)
{
unsigned long a, hash = 0;
for (;;) {
+ if (!len)
+ goto done;
a = load_unaligned_zeropad(name);
if (len < sizeof(unsigned long))
break;
hash = mix_hash(hash + a);
name += sizeof(unsigned long);
len -= sizeof(unsigned long);
- if (!len)
- goto done;
}
hash += a & bytemask_from_count(len);
done:
@@ -1842,6 +1843,29 @@ done:
}
EXPORT_SYMBOL(full_name_hash);
+/* Return the "hash_len" (hash and length) of a null-terminated string */
+u64 hashlen_string(const char *name)
+{
+ unsigned long a, adata, mask, hash, len;
+ const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
+
+ hash = a = 0;
+ len = -sizeof(unsigned long);
+ do {
+ hash = mix_hash(hash + a);
+ len += sizeof(unsigned long);
+ a = load_unaligned_zeropad(name+len);
+ } while (!has_zero(a, &adata, &constants));
+
+ adata = prep_zero_mask(a, adata, &constants);
+ mask = create_zero_mask(adata);
+ hash += a & zero_bytemask(mask);
+ len += find_zero(mask);
+
+ return hashlen_create(fold_hash(hash), len);
+}
+EXPORT_SYMBOL(hashlen_string);
+
/*
* Calculate the length and hash of the path component, and
* return the "hash_len" as the result.
@@ -1872,15 +1896,32 @@ static inline u64 hash_name(const char *name)
#else
-unsigned int full_name_hash(const unsigned char *name, unsigned int len)
+/* Return the hash of a string of known length */
+unsigned int full_name_hash(const char *name, unsigned int len)
{
unsigned long hash = init_name_hash();
while (len--)
- hash = partial_name_hash(*name++, hash);
+ hash = partial_name_hash((unsigned char)*name++, hash);
return end_name_hash(hash);
}
EXPORT_SYMBOL(full_name_hash);
+/* Return the "hash_len" (hash and length) of a null-terminated string */
+u64 hash_string(const char *name)
+{
+ unsigned long hash = init_name_hash();
+ unsigned long len = 0, c;
+
+ c = (unsigned char)*name;
+ do {
+ len++;
+ hash = partial_name_hash(c, hash);
+ c = (unsigned char)name[len];
+ } while (c);
+ return hashlen_create(end_name_hash(hash), len);
+}
+EXPORT_SYMBOL(hash_string);
+
/*
* We know there's a real path component here of at least
* one character.
diff --git a/include/linux/stringhash.h b/include/linux/stringhash.h
index 2eaaaf6d..451771d9 100644
--- a/include/linux/stringhash.h
+++ b/include/linux/stringhash.h
@@ -1,7 +1,8 @@
#ifndef __LINUX_STRINGHASH_H
#define __LINUX_STRINGHASH_H
-#include <linux/types.h>
+#include <linux/compiler.h> /* For __pure */
+#include <linux/types.h> /* For u32, u64 */
/*
* Routines for hashing strings of bytes to a 32-bit hash value.
@@ -59,7 +60,7 @@ static inline unsigned long end_name_hash(unsigned long hash)
*
* If not set, this falls back to a wrapper around the preceding.
*/
-extern unsigned int full_name_hash(const unsigned char *, unsigned int);
+extern unsigned int __pure full_name_hash(const char *, unsigned int);
/*
* A hash_len is a u64 with the hash of a string in the low
@@ -69,4 +70,7 @@ extern unsigned int full_name_hash(const unsigned char *, unsigned int);
#define hashlen_len(hashlen) ((u32)((hashlen) >> 32))
#define hashlen_create(hash, len) ((u64)(len)<<32 | (u32)(hash))
+/* Return the "hash_len" (hash and length) of a null-terminated string */
+extern u64 __pure hashlen_string(const char *name);
+
#endif /* __LINUX_STRINGHASH_H */
--
2.8.1
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