fs/ext4/hash.c

   1 /*
   2  *  linux/fs/ext4/hash.c
   3  *
   4  * Copyright (C) 2002 by Theodore Ts'o
   5  *
   6  * This file is released under the GPL v2.
   7  *
   8  * This file may be redistributed under the terms of the GNU Public
   9  * License.
  10  */
  11
  12 #include <linux/fs.h>
  13 #include <linux/jbd2.h>
  14 #include <linux/ext4_fs.h>
  15 #include <linux/cryptohash.h>
  16
  17 #define DELTA 0x9E3779B9
  18
  19 static void TEA_transform(__u32 buf[4], __u32 const in[])
  20 {
  21         __u32   sum = 0;
  22         __u32   b0 = buf[0], b1 = buf[1];
  23         __u32   a = in[0], b = in[1], c = in[2], d = in[3];
  24         int     n = 16;
  25
  26         do {
  27                 sum += DELTA;
  28                 b0 += ((b1 << 4)+a) ^ (b1+sum) ^ ((b1 >> 5)+b);
  29                 b1 += ((b0 << 4)+c) ^ (b0+sum) ^ ((b0 >> 5)+d);
  30         } while(--n);
  31
  32         buf[0] += b0;
  33         buf[1] += b1;
  34 }
  35
  36
  37 /* The old legacy hash */
  38 static __u32 dx_hack_hash (const char *name, int len)
  39 {
  40         __u32 hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
  41         while (len--) {
  42                 __u32 hash = hash1 + (hash0 ^ (*name++ * 7152373));
  43
  44                 if (hash & 0x80000000) hash -= 0x7fffffff;
  45                 hash1 = hash0;
  46                 hash0 = hash;
  47         }
  48         return (hash0 << 1);
  49 }
  50
  51 static void str2hashbuf(const char *msg, int len, __u32 *buf, int num)
  52 {
  53         __u32   pad, val;
  54         int     i;
  55
  56         pad = (__u32)len | ((__u32)len << 8);
  57         pad |= pad << 16;
  58
  59         val = pad;
  60         if (len > num*4)
  61                 len = num * 4;
  62         for (i=0; i < len; i++) {
  63                 if ((i % 4) == 0)
  64                         val = pad;
  65                 val = msg[i] + (val << 8);
  66                 if ((i % 4) == 3) {
  67                         *buf++ = val;
  68                         val = pad;
  69                         num--;
  70                 }
  71         }
  72         if (--num >= 0)
  73                 *buf++ = val;
  74         while (--num >= 0)
  75                 *buf++ = pad;
  76 }
  77
  78 /*
  79  * Returns the hash of a filename.  If len is 0 and name is NULL, then
  80  * this function can be used to test whether or not a hash version is
  81  * supported.
  82  *
  83  * The seed is an 4 longword (32 bits) "secret" which can be used to
  84  * uniquify a hash.  If the seed is all zero's, then some default seed
  85  * may be used.
  86  *
  87  * A particular hash version specifies whether or not the seed is
  88  * represented, and whether or not the returned hash is 32 bits or 64
  89  * bits.  32 bit hashes will return 0 for the minor hash.
  90  */
  91 int ext4fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
  92 {
  93         __u32   hash;
  94         __u32   minor_hash = 0;
  95         const char      *p;
  96         int             i;
  97         __u32           in[8], buf[4];
  98
  99         /* Initialize the default seed for the hash checksum functions */
 100         buf[0] = 0x67452301;
 101         buf[1] = 0xefcdab89;
 102         buf[2] = 0x98badcfe;
 103         buf[3] = 0x10325476;
 104
 105         /* Check to see if the seed is all zero's */
 106         if (hinfo->seed) {
 107                 for (i=0; i < 4; i++) {
 108                         if (hinfo->seed[i])
 109                                 break;
 110                 }
 111                 if (i < 4)
 112                         memcpy(buf, hinfo->seed, sizeof(buf));
 113         }
 114
 115         switch (hinfo->hash_version) {
 116         case DX_HASH_LEGACY:
 117                 hash = dx_hack_hash(name, len);
 118                 break;
 119         case DX_HASH_HALF_MD4:
 120                 p = name;
 121                 while (len > 0) {
 122                         str2hashbuf(p, len, in, 8);
 123                         half_md4_transform(buf, in);
 124                         len -= 32;
 125                         p += 32;
 126                 }
 127                 minor_hash = buf[2];
 128                 hash = buf[1];
 129                 break;
 130         case DX_HASH_TEA:
 131                 p = name;
 132                 while (len > 0) {
 133                         str2hashbuf(p, len, in, 4);
 134                         TEA_transform(buf, in);
 135                         len -= 16;
 136                         p += 16;
 137                 }
 138                 hash = buf[0];
 139                 minor_hash = buf[1];
 140                 break;
 141         default:
 142                 hinfo->hash = 0;
 143                 return -1;
 144         }
 145         hash = hash & ~1;
 146         if (hash == (EXT4_HTREE_EOF << 1))
 147                 hash = (EXT4_HTREE_EOF-1) << 1;
 148         hinfo->hash = hash;
 149         hinfo->minor_hash = minor_hash;
 150         return 0;
 151 }