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>

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 @@
+
+#include "types.h"
+
+/*
+ * Robert Jenkin's hash function.
+ * http://burtleburtle.net/bob/hash/evahash.html
+ * This is in the public domain.
+ */
+#define mix(a, b, c)                                            \
+        do {                                                    \
+                a = a - b;  a = a - c;  a = a ^ (c >> 13);      \
+                b = b - c;  b = b - a;  b = b ^ (a << 8);       \
+                c = c - a;  c = c - b;  c = c ^ (b >> 13);      \
+                a = a - b;  a = a - c;  a = a ^ (c >> 12);      \
+                b = b - c;  b = b - a;  b = b ^ (a << 16);      \
+                c = c - a;  c = c - b;  c = c ^ (b >> 5);       \
+                a = a - b;  a = a - c;  a = a ^ (c >> 3);       \
+                b = b - c;  b = b - a;  b = b ^ (a << 10);      \
+                c = c - a;  c = c - b;  c = c ^ (b >> 15);      \
+        } while (0)
+
+unsigned ceph_str_hash_rjenkins(const char *str, unsigned length)
+{
+        const unsigned char *k = (const unsigned char *)str;
+        __u32 a, b, c;  /* the internal state */
+        __u32 len;      /* how many key bytes still need mixing */
+
+        /* Set up the internal state */
+        len = length;
+        a = 0x9e3779b9;      /* the golden ratio; an arbitrary value */
+        b = a;
+        c = 0;               /* variable initialization of internal state */
+
+        /* handle most of the key */
+        while (len >= 12) {
+                a = a + (k[0] + ((__u32)k[1] << 8) + ((__u32)k[2] << 16) +
+                         ((__u32)k[3] << 24));
+                b = b + (k[4] + ((__u32)k[5] << 8) + ((__u32)k[6] << 16) +
+                         ((__u32)k[7] << 24));
+                c = c + (k[8] + ((__u32)k[9] << 8) + ((__u32)k[10] << 16) +
+                         ((__u32)k[11] << 24));
+                mix(a, b, c);
+                k = k + 12;
+                len = len - 12;
+        }
+
+        /* handle the last 11 bytes */
+        c = c + length;
+        switch (len) {            /* all the case statements fall through */
+        case 11:
+                c = c + ((__u32)k[10] << 24);
+        case 10:
+                c = c + ((__u32)k[9] << 16);
+        case 9:
+                c = c + ((__u32)k[8] << 8);
+                /* the first byte of c is reserved for the length */
+        case 8:
+                b = b + ((__u32)k[7] << 24);
+        case 7:
+                b = b + ((__u32)k[6] << 16);
+        case 6:
+                b = b + ((__u32)k[5] << 8);
+        case 5:
+                b = b + k[4];
+        case 4:
+                a = a + ((__u32)k[3] << 24);
+        case 3:
+                a = a + ((__u32)k[2] << 16);
+        case 2:
+                a = a + ((__u32)k[1] << 8);
+        case 1:
+                a = a + k[0];
+                /* case 0: nothing left to add */
+        }
+        mix(a, b, c);
+
+        return c;
+}
+
+/*
+ * linux dcache hash
+ */
+unsigned ceph_str_hash_linux(const char *str, unsigned length)
+{
+        unsigned long hash = 0;
+        unsigned char c;
+
+        while (length-- > 0) {
+                c = *str++;
+                hash = (hash + (c << 4) + (c >> 4)) * 11;
+        }
+        return hash;
+}
+
+
+unsigned ceph_str_hash(int type, const char *s, unsigned len)
+{
+        switch (type) {
+        case CEPH_STR_HASH_LINUX:
+                return ceph_str_hash_linux(s, len);
+        case CEPH_STR_HASH_RJENKINS:
+                return ceph_str_hash_rjenkins(s, len);
+        default:
+                return -1;
+        }
+}
+
+const char *ceph_str_hash_name(int type) 
+{
+        switch (type) {
+        case CEPH_STR_HASH_LINUX:
+                return "linux";
+        case CEPH_STR_HASH_RJENKINS:
+                return "rjenkins";
+        default:
+                return "unknown";
+        }
+}