com32/lib/syslinux/setadv.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2007-2008 H. Peter Anvin - All Rights Reserved
   4  *   Copyright 2009 Intel Corporation; author: H. Peter Anvin
   5  *
   6  *   Permission is hereby granted, free of charge, to any person
   7  *   obtaining a copy of this software and associated documentation
   8  *   files (the "Software"), to deal in the Software without
   9  *   restriction, including without limitation the rights to use,
  10  *   copy, modify, merge, publish, distribute, sublicense, and/or
  11  *   sell copies of the Software, and to permit persons to whom
  12  *   the Software is furnished to do so, subject to the following
  13  *   conditions:
  14  *
  15  *   The above copyright notice and this permission notice shall
  16  *   be included in all copies or substantial portions of the Software.
  17  *
  18  *   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  19  *   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
  20  *   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  21  *   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  22  *   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  23  *   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  24  *   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  25  *   OTHER DEALINGS IN THE SOFTWARE.
  26  *
  27  * ----------------------------------------------------------------------- */
  28
  29 /*
  30  * syslinux/setadv.c
  31  *
  32  * (Over)write a data item in the auxilliary data vector.  To
  33  * delete an item, set its length to zero.
  34  *
  35  * Return 0 on success, -1 on error, and set errno.
  36  *
  37  * NOTE: Data is not written to disk unless
  38  * syslinux_adv_write() is called.
  39  */
  40
  41 #include <syslinux/adv.h>
  42 #include <klibc/compiler.h>
  43 #include <inttypes.h>
  44 #include <string.h>
  45 #include <errno.h>
  46 #include <alloca.h>
  47
  48 int syslinux_setadv(int tag, size_t size, const void *data)
  49 {
  50     uint8_t *p, *advtmp;
  51     size_t rleft, left;
  52
  53     if ((unsigned)tag - 1 > 254) {
  54         errno = EINVAL;
  55         return -1;              /* Impossible tag value */
  56     }
  57
  58     if (size > 255) {
  59         errno = ENOSPC;         /* Max 255 bytes for a data item */
  60         return -1;
  61     }
  62
  63     rleft = left = syslinux_adv_size();
  64     p = advtmp = alloca(left);
  65     memcpy(p, syslinux_adv_ptr(), left);        /* Make working copy */
  66
  67     while (rleft >= 2) {
  68         uint8_t ptag = p[0];
  69         size_t plen = p[1] + 2;
  70
  71         if (ptag == ADV_END)
  72             break;
  73
  74         if (ptag == tag) {
  75             /* Found our tag.  Delete it. */
  76
  77             if (plen >= rleft) {
  78                 /* Entire remainder is our tag */
  79                 break;
  80             }
  81             memmove(p, p + plen, rleft - plen);
  82             rleft -= plen;      /* Fewer bytes to read, but not to write */
  83         } else {
  84             /* Not our tag */
  85             if (plen > rleft)
  86                 break;          /* Corrupt tag (overrun) - overwrite it */
  87
  88             left -= plen;
  89             rleft -= plen;
  90             p += plen;
  91         }
  92     }
  93
  94     /* Now (p, left) reflects the position to write in and how much space
  95        we have for our data. */
  96
  97     if (size) {
  98         if (left < size + 2) {
  99             errno = ENOSPC;     /* Not enough space for data */
 100             return -1;
 101         }
 102
 103         *p++ = tag;
 104         *p++ = size;
 105         memcpy(p, data, size);
 106         p += size;
 107         left -= size + 2;
 108     }
 109
 110     memset(p, 0, left);
 111
 112     /* If we got here, everything went OK, commit the write to low memory */
 113     memcpy(syslinux_adv_ptr(), advtmp, syslinux_adv_size());
 114
 115     return 0;
 116 }