lib/ext2fs/ext_attr.c

   1 /*
   2  * ext_attr.c --- extended attribute blocks
   3  *
   4  * Copyright (C) 2001 Andreas Gruenbacher, <a.gruenbacher@computer.org>
   5  *
   6  * Copyright (C) 2002 Theodore Ts'o.
   7  *
   8  * %Begin-Header%
   9  * This file may be redistributed under the terms of the GNU Public
  10  * License.
  11  * %End-Header%
  12  */
  13
  14 #include <stdio.h>
  15 #if HAVE_UNISTD_H
  16 #include <unistd.h>
  17 #endif
  18 #include <string.h>
  19 #include <time.h>
  20
  21 #include "ext2_fs.h"
  22 #include "ext2_ext_attr.h"
  23
  24 #include "ext2fs.h"
  25
  26 #define NAME_HASH_SHIFT 5
  27 #define VALUE_HASH_SHIFT 16
  28
  29 /*
  30  * ext2_xattr_hash_entry()
  31  *
  32  * Compute the hash of an extended attribute.
  33  */
  34 __u32 ext2fs_ext_attr_hash_entry(struct ext2_ext_attr_entry *entry, void *data)
  35 {
  36         __u32 hash = 0;
  37         char *name = ((char *) entry) + sizeof(struct ext2_ext_attr_entry);
  38         int n;
  39
  40         for (n = 0; n < entry->e_name_len; n++) {
  41                 hash = (hash << NAME_HASH_SHIFT) ^
  42                        (hash >> (8*sizeof(hash) - NAME_HASH_SHIFT)) ^
  43                        *name++;
  44         }
  45
  46         /* The hash needs to be calculated on the data in little-endian. */
  47         if (entry->e_value_block == 0 && entry->e_value_size != 0) {
  48                 __u32 *value = (__u32 *)data;
  49                 for (n = (entry->e_value_size + EXT2_EXT_ATTR_ROUND) >>
  50                          EXT2_EXT_ATTR_PAD_BITS; n; n--) {
  51                         hash = (hash << VALUE_HASH_SHIFT) ^
  52                                (hash >> (8*sizeof(hash) - VALUE_HASH_SHIFT)) ^
  53                                ext2fs_le32_to_cpu(*value++);
  54                 }
  55         }
  56
  57         return hash;
  58 }
  59
  60 #undef NAME_HASH_SHIFT
  61 #undef VALUE_HASH_SHIFT
  62
  63 errcode_t ext2fs_read_ext_attr(ext2_filsys fs, blk_t block, void *buf)
  64 {
  65         errcode_t       retval;
  66
  67         retval = io_channel_read_blk(fs->io, block, 1, buf);
  68         if (retval)
  69                 return retval;
  70 #ifdef WORDS_BIGENDIAN
  71         ext2fs_swap_ext_attr(buf, buf, fs->blocksize, 1);
  72 #endif
  73         return 0;
  74 }
  75
  76 errcode_t ext2fs_write_ext_attr(ext2_filsys fs, blk_t block, void *inbuf)
  77 {
  78         errcode_t       retval;
  79         char            *write_buf;
  80         char            *buf = NULL;
  81
  82 #ifdef WORDS_BIGENDIAN
  83         retval = ext2fs_get_mem(fs->blocksize, &buf);
  84         if (retval)
  85                 return retval;
  86         write_buf = buf;
  87         ext2fs_swap_ext_attr(buf, inbuf, fs->blocksize, 1);
  88 #else
  89         write_buf = (char *) inbuf;
  90 #endif
  91         retval = io_channel_write_blk(fs->io, block, 1, write_buf);
  92         if (buf)
  93                 ext2fs_free_mem(&buf);
  94         if (!retval)
  95                 ext2fs_mark_changed(fs);
  96         return retval;
  97 }
  98
  99 /*
 100  * This function adjusts the reference count of the EA block.
 101  */
 102 errcode_t ext2fs_adjust_ea_refcount(ext2_filsys fs, blk_t blk,
 103                                     char *block_buf, int adjust,
 104                                     __u32 *newcount)
 105 {
 106         errcode_t       retval;
 107         struct ext2_ext_attr_header *header;
 108         char    *buf = 0;
 109
 110         if ((blk >= fs->super->s_blocks_count) ||
 111             (blk < fs->super->s_first_data_block))
 112                 return EXT2_ET_BAD_EA_BLOCK_NUM;
 113
 114         if (!block_buf) {
 115                 retval = ext2fs_get_mem(fs->blocksize, &buf);
 116                 if (retval)
 117                         return retval;
 118                 block_buf = buf;
 119         }
 120
 121         retval = ext2fs_read_ext_attr(fs, blk, block_buf);
 122         if (retval)
 123                 goto errout;
 124
 125         header = (struct ext2_ext_attr_header *) block_buf;
 126         header->h_refcount += adjust;
 127         if (newcount)
 128                 *newcount = header->h_refcount;
 129
 130         retval = ext2fs_write_ext_attr(fs, blk, block_buf);
 131         if (retval)
 132                 goto errout;
 133
 134 errout:
 135         if (buf)
 136                 ext2fs_free_mem(&buf);
 137         return retval;
 138 }