Pull out string hash to <linux/stringhash.h>

... so they can be used without the rest of <linux/dcache.h> The hashlen_* macros will make sense next patch.

George Spelvin committed 10 years ago

Commit f4bcbe71 parent 0fed3ac2 files · +73 −26Browse files

Unified · Split

2 files

include/linux/dcache.h +1 −26
include/linux/stringhash.h +72 −0

@@ -10,6 +10,7 @@ · 9 unmodified lines
10	10	#include <linux/cache.h>
11	11	#include <linux/rcupdate.h>
12	12	#include <linux/lockref.h>
	13	+#include <linux/stringhash.h>
13	14
14	15	struct path;
15	16	struct vfsmount;
@@ -52,9 +53,6 @@ struct qstr { · 36 unmodified lines
52	53	};
53	54
54	55	#define QSTR_INIT(n,l) { { { .len = l } }, .name = n }
55		−#define hashlen_hash(hashlen) ((u32) (hashlen))
56		−#define hashlen_len(hashlen) ((u32)((hashlen) >> 32))
57		−#define hashlen_create(hash,len) (((u64)(len)<<32)\|(u32)(hash))
58	56
59	57	struct dentry_stat_t {
60	58	long nr_dentry;
@@ -65,29 +63,6 @@ struct dentry_stat_t { · 4 unmodified lines
65	63	};
66	64	extern struct dentry_stat_t dentry_stat;
67	65
68		−/* Name hashing routines. Initial hash value */
69		−/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */
70		−#define init_name_hash() 0
71		−
72		−/* partial hash update function. Assume roughly 4 bits per character */
73		−static inline unsigned long
74		−partial_name_hash(unsigned long c, unsigned long prevhash)
75		−{
76		− return (prevhash + (c << 4) + (c >> 4)) * 11;
77		−}
78		−
79		−/*
80		− * Finally: cut down the number of bits to a int value (and try to avoid
81		− * losing bits)
82		− */
83		−static inline unsigned long end_name_hash(unsigned long hash)
84		−{
85		− return (unsigned int) hash;
86		−}
87		−
88		−/* Compute the hash for a name string. */
89		−extern unsigned int full_name_hash(const unsigned char *, unsigned int);
90		−
91	66	/*
92	67	* Try to keep struct dentry aligned on 64 byte cachelines (this will
93	68	* give reasonable cacheline footprint with larger lines without the

include/linux/stringhash.h+72−0

@@ -0,0 +1,72 @@
	1	+#ifndef __LINUX_STRINGHASH_H
	2	+#define __LINUX_STRINGHASH_H
	3	+
	4	+#include <linux/types.h>
	5	+
	6	+/*
	7	+ * Routines for hashing strings of bytes to a 32-bit hash value.
	8	+ *
	9	+ * These hash functions are NOT GUARANTEED STABLE between kernel
	10	+ * versions, architectures, or even repeated boots of the same kernel.
	11	+ * (E.g. they may depend on boot-time hardware detection or be
	12	+ * deliberately randomized.)
	13	+ *
	14	+ * They are also not intended to be secure against collisions caused by
	15	+ * malicious inputs; much slower hash functions are required for that.
	16	+ *
	17	+ * They are optimized for pathname components, meaning short strings.
	18	+ * Even if a majority of files have longer names, the dynamic profile of
	19	+ * pathname components skews short due to short directory names.
	20	+ * (E.g. /usr/lib/libsesquipedalianism.so.3.141.)
	21	+ */
	22	+
	23	+/*
	24	+ * Version 1: one byte at a time. Example of use:
	25	+ *
	26	+ * unsigned long hash = init_name_hash;
	27	+ * while (*p)
	28	+ * hash = partial_name_hash(tolower(*p++), hash);
	29	+ * hash = end_name_hash(hash);
	30	+ *
	31	+ * Although this is designed for bytes, fs/hfsplus/unicode.c
	32	+ * abuses it to hash 16-bit values.
	33	+ */
	34	+
	35	+/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */
	36	+#define init_name_hash() 0
	37	+
	38	+/* partial hash update function. Assume roughly 4 bits per character */
	39	+static inline unsigned long
	40	+partial_name_hash(unsigned long c, unsigned long prevhash)
	41	+{
	42	+ return (prevhash + (c << 4) + (c >> 4)) * 11;
	43	+}
	44	+
	45	+/*
	46	+ * Finally: cut down the number of bits to a int value (and try to avoid
	47	+ * losing bits)
	48	+ */
	49	+static inline unsigned long end_name_hash(unsigned long hash)
	50	+{
	51	+ return (unsigned int)hash;
	52	+}
	53	+
	54	+/*
	55	+ * Version 2: One word (32 or 64 bits) at a time.
	56	+ * If CONFIG_DCACHE_WORD_ACCESS is defined (meaning <asm/word-at-a-time.h>
	57	+ * exists, which describes major Linux platforms like x86 and ARM), then
	58	+ * this computes a different hash function much faster.
	59	+ *
	60	+ * If not set, this falls back to a wrapper around the preceding.
	61	+ */
	62	+extern unsigned int full_name_hash(const unsigned char *, unsigned int);
	63	+
	64	+/*
	65	+ * A hash_len is a u64 with the hash of a string in the low
	66	+ * half and the length in the high half.
	67	+ */
	68	+#define hashlen_hash(hashlen) ((u32)(hashlen))
	69	+#define hashlen_len(hashlen) ((u32)((hashlen) >> 32))
	70	+#define hashlen_create(hash, len) ((u64)(len)<<32 \| (u32)(hash))
	71	+
	72	+#endif /* __LINUX_STRINGHASH_H */