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authorSage Weil <sage@newdream.net>2009-11-07 00:55:25 -0500
committerSage Weil <sage@newdream.net>2009-11-07 00:55:25 -0500
commit1654dd0cf5ee1827322aca156af7d96d757201c7 (patch)
treeba71b1a1e214b929937f02a1794b3d32b8ff1342 /fs/ceph/ceph_hash.c
parentcfbbcd24a6bfd794295ee7ad76dfbff40ad6b934 (diff)
ceph: make object hash a pg_pool property
The object will be hashed to a placement seed (ps) based on the pg_pool's hash function. This allows new hashes to be introduced into an existing object store, or selection of a hash appropriate to the objects that will be stored in a particular pool. Signed-off-by: Sage Weil <sage@newdream.net>
Diffstat (limited to 'fs/ceph/ceph_hash.c')
-rw-r--r--fs/ceph/ceph_hash.c118
1 files changed, 118 insertions, 0 deletions
diff --git a/fs/ceph/ceph_hash.c b/fs/ceph/ceph_hash.c
new file mode 100644
index 000000000000..ac8be54631fe
--- /dev/null
+++ b/fs/ceph/ceph_hash.c
@@ -0,0 +1,118 @@
1
2#include "types.h"
3
4/*
5 * Robert Jenkin's hash function.
6 * http://burtleburtle.net/bob/hash/evahash.html
7 * This is in the public domain.
8 */
9#define mix(a, b, c) \
10 do { \
11 a = a - b; a = a - c; a = a ^ (c >> 13); \
12 b = b - c; b = b - a; b = b ^ (a << 8); \
13 c = c - a; c = c - b; c = c ^ (b >> 13); \
14 a = a - b; a = a - c; a = a ^ (c >> 12); \
15 b = b - c; b = b - a; b = b ^ (a << 16); \
16 c = c - a; c = c - b; c = c ^ (b >> 5); \
17 a = a - b; a = a - c; a = a ^ (c >> 3); \
18 b = b - c; b = b - a; b = b ^ (a << 10); \
19 c = c - a; c = c - b; c = c ^ (b >> 15); \
20 } while (0)
21
22unsigned ceph_str_hash_rjenkins(const char *str, unsigned length)
23{
24 const unsigned char *k = (const unsigned char *)str;
25 __u32 a, b, c; /* the internal state */
26 __u32 len; /* how many key bytes still need mixing */
27
28 /* Set up the internal state */
29 len = length;
30 a = 0x9e3779b9; /* the golden ratio; an arbitrary value */
31 b = a;
32 c = 0; /* variable initialization of internal state */
33
34 /* handle most of the key */
35 while (len >= 12) {
36 a = a + (k[0] + ((__u32)k[1] << 8) + ((__u32)k[2] << 16) +
37 ((__u32)k[3] << 24));
38 b = b + (k[4] + ((__u32)k[5] << 8) + ((__u32)k[6] << 16) +
39 ((__u32)k[7] << 24));
40 c = c + (k[8] + ((__u32)k[9] << 8) + ((__u32)k[10] << 16) +
41 ((__u32)k[11] << 24));
42 mix(a, b, c);
43 k = k + 12;
44 len = len - 12;
45 }
46
47 /* handle the last 11 bytes */
48 c = c + length;
49 switch (len) { /* all the case statements fall through */
50 case 11:
51 c = c + ((__u32)k[10] << 24);
52 case 10:
53 c = c + ((__u32)k[9] << 16);
54 case 9:
55 c = c + ((__u32)k[8] << 8);
56 /* the first byte of c is reserved for the length */
57 case 8:
58 b = b + ((__u32)k[7] << 24);
59 case 7:
60 b = b + ((__u32)k[6] << 16);
61 case 6:
62 b = b + ((__u32)k[5] << 8);
63 case 5:
64 b = b + k[4];
65 case 4:
66 a = a + ((__u32)k[3] << 24);
67 case 3:
68 a = a + ((__u32)k[2] << 16);
69 case 2:
70 a = a + ((__u32)k[1] << 8);
71 case 1:
72 a = a + k[0];
73 /* case 0: nothing left to add */
74 }
75 mix(a, b, c);
76
77 return c;
78}
79
80/*
81 * linux dcache hash
82 */
83unsigned ceph_str_hash_linux(const char *str, unsigned length)
84{
85 unsigned long hash = 0;
86 unsigned char c;
87
88 while (length-- > 0) {
89 c = *str++;
90 hash = (hash + (c << 4) + (c >> 4)) * 11;
91 }
92 return hash;
93}
94
95
96unsigned ceph_str_hash(int type, const char *s, unsigned len)
97{
98 switch (type) {
99 case CEPH_STR_HASH_LINUX:
100 return ceph_str_hash_linux(s, len);
101 case CEPH_STR_HASH_RJENKINS:
102 return ceph_str_hash_rjenkins(s, len);
103 default:
104 return -1;
105 }
106}
107
108const char *ceph_str_hash_name(int type)
109{
110 switch (type) {
111 case CEPH_STR_HASH_LINUX:
112 return "linux";
113 case CEPH_STR_HASH_RJENKINS:
114 return "rjenkins";
115 default:
116 return "unknown";
117 }
118}