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author | George Spelvin <linux@sciencehorizons.net> | 2016-05-20 07:26:00 -0400 |
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committer | George Spelvin <linux@sciencehorizons.net> | 2016-05-28 15:42:40 -0400 |
commit | f4bcbe792b8f434e32487cff9d9e30ab45a3ce02 (patch) | |
tree | 923b7a959d8de2f8beed465a7d987dd21ec64f6b | |
parent | 0fed3ac866eabf01924457921ee3684c8e4c9005 (diff) | |
download | linux-f4bcbe792b8f434e32487cff9d9e30ab45a3ce02.tar.gz linux-f4bcbe792b8f434e32487cff9d9e30ab45a3ce02.tar.bz2 linux-f4bcbe792b8f434e32487cff9d9e30ab45a3ce02.zip |
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.
Signed-off-by: George Spelvin <linux@sciencehorizons.net>
-rw-r--r-- | include/linux/dcache.h | 27 | ||||
-rw-r--r-- | include/linux/stringhash.h | 72 |
2 files changed, 73 insertions, 26 deletions
diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 7e9422cb5989..0f9a977c334f 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -10,6 +10,7 @@ #include <linux/cache.h> #include <linux/rcupdate.h> #include <linux/lockref.h> +#include <linux/stringhash.h> struct path; struct vfsmount; @@ -52,9 +53,6 @@ struct qstr { }; #define QSTR_INIT(n,l) { { { .len = l } }, .name = n } -#define hashlen_hash(hashlen) ((u32) (hashlen)) -#define hashlen_len(hashlen) ((u32)((hashlen) >> 32)) -#define hashlen_create(hash,len) (((u64)(len)<<32)|(u32)(hash)) struct dentry_stat_t { long nr_dentry; @@ -65,29 +63,6 @@ struct dentry_stat_t { }; extern struct dentry_stat_t dentry_stat; -/* Name hashing routines. Initial hash value */ -/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */ -#define init_name_hash() 0 - -/* partial hash update function. Assume roughly 4 bits per character */ -static inline unsigned long -partial_name_hash(unsigned long c, unsigned long prevhash) -{ - return (prevhash + (c << 4) + (c >> 4)) * 11; -} - -/* - * Finally: cut down the number of bits to a int value (and try to avoid - * losing bits) - */ -static inline unsigned long end_name_hash(unsigned long hash) -{ - return (unsigned int) hash; -} - -/* Compute the hash for a name string. */ -extern unsigned int full_name_hash(const unsigned char *, unsigned int); - /* * Try to keep struct dentry aligned on 64 byte cachelines (this will * give reasonable cacheline footprint with larger lines without the diff --git a/include/linux/stringhash.h b/include/linux/stringhash.h new file mode 100644 index 000000000000..2eaaaf6d2776 --- /dev/null +++ b/include/linux/stringhash.h @@ -0,0 +1,72 @@ +#ifndef __LINUX_STRINGHASH_H +#define __LINUX_STRINGHASH_H + +#include <linux/types.h> + +/* + * Routines for hashing strings of bytes to a 32-bit hash value. + * + * These hash functions are NOT GUARANTEED STABLE between kernel + * versions, architectures, or even repeated boots of the same kernel. + * (E.g. they may depend on boot-time hardware detection or be + * deliberately randomized.) + * + * They are also not intended to be secure against collisions caused by + * malicious inputs; much slower hash functions are required for that. + * + * They are optimized for pathname components, meaning short strings. + * Even if a majority of files have longer names, the dynamic profile of + * pathname components skews short due to short directory names. + * (E.g. /usr/lib/libsesquipedalianism.so.3.141.) + */ + +/* + * Version 1: one byte at a time. Example of use: + * + * unsigned long hash = init_name_hash; + * while (*p) + * hash = partial_name_hash(tolower(*p++), hash); + * hash = end_name_hash(hash); + * + * Although this is designed for bytes, fs/hfsplus/unicode.c + * abuses it to hash 16-bit values. + */ + +/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */ +#define init_name_hash() 0 + +/* partial hash update function. Assume roughly 4 bits per character */ +static inline unsigned long +partial_name_hash(unsigned long c, unsigned long prevhash) +{ + return (prevhash + (c << 4) + (c >> 4)) * 11; +} + +/* + * Finally: cut down the number of bits to a int value (and try to avoid + * losing bits) + */ +static inline unsigned long end_name_hash(unsigned long hash) +{ + return (unsigned int)hash; +} + +/* + * Version 2: One word (32 or 64 bits) at a time. + * If CONFIG_DCACHE_WORD_ACCESS is defined (meaning <asm/word-at-a-time.h> + * exists, which describes major Linux platforms like x86 and ARM), then + * this computes a different hash function much faster. + * + * If not set, this falls back to a wrapper around the preceding. + */ +extern unsigned int full_name_hash(const unsigned char *, unsigned int); + +/* + * A hash_len is a u64 with the hash of a string in the low + * half and the length in the high half. + */ +#define hashlen_hash(hashlen) ((u32)(hashlen)) +#define hashlen_len(hashlen) ((u32)((hashlen) >> 32)) +#define hashlen_create(hash, len) ((u64)(len)<<32 | (u32)(hash)) + +#endif /* __LINUX_STRINGHASH_H */ |