commands/cdprobe/cdprobe.c

   1 /* This file contains some code to guess where we have to load the
   2  * RAM image device from, if started from CD. (In this case it's hard
   3  * to tell where this is without diving into BIOS heuristics.)
   4  *
   5  * There is some nasty hard-codery in here ( MINIX cd label) that can be
   6  * improved on.
   7  *
   8  * Changes:
   9  *   Jul 14, 2005   Created (Ben Gras)
  10  *   Feb 10, 2006   Changed into a standalone program (Philip Homburg)
  11  */
  12
  13 #define CD_SECTOR       2048
  14 #define SUPER_OFF       1024
  15 #define AT_MINORS       8
  16 #define MAGIC_OFF       24
  17
  18 #include <errno.h>
  19 #include <fcntl.h>
  20 #include <stdio.h>
  21 #include <stdlib.h>
  22 #include <string.h>
  23 #include <unistd.h>
  24
  25 #include "mfs/const.h"
  26
  27 char pvd[CD_SECTOR];
  28
  29 /*===========================================================================*
  30  *                              cdprobe                                      *
  31  *===========================================================================*/
  32 int main(void)
  33 {
  34         int controller, disk, r, fd, minor, found;
  35         off_t pos;
  36         u16_t *magicp;
  37         char name1[]= "/dev/c0dX";
  38         char name2[]= "/dev/c0dXpY";
  39         int probelist[AT_MINORS] = { 2, 3, 1, 0, 6, 7, 5, 4 };
  40
  41         found= 0;
  42         for(controller = 0; controller <= 1; controller++) {
  43            name1[6] = '0' + controller;
  44            name2[6] = '0' + controller;
  45            for(disk = 0; disk < AT_MINORS; disk++) {
  46                 name1[8]= '0' + probelist[disk];
  47
  48                 fprintf(stderr, "Trying %s  \r", name1);
  49                 fflush(stderr);
  50
  51                 fd = open(name1, O_RDONLY);
  52                 if (fd < 0)
  53                 {
  54                         if (errno != ENXIO)
  55                         {
  56                                 fprintf(stderr, "open '%s' failed: %s\n",
  57                                         name1, strerror(errno));
  58                         }
  59                         continue;
  60                 }
  61
  62                 pos= lseek(fd, 16*CD_SECTOR, SEEK_SET);
  63                 if (pos != 16*CD_SECTOR)
  64                 {
  65                         /* Strange, do we need to issue a warning? */
  66                         close(fd);
  67                         continue;
  68                 }
  69                 r = read(fd, pvd, sizeof(pvd));
  70                 if (r != sizeof(pvd))
  71                 {
  72                         fprintf(stderr,
  73                                 "error reading CD label from '%s': %s\n",
  74                                 name1, strerror(errno));
  75                         close(fd);
  76                         continue;
  77                 }
  78                 close(fd);
  79
  80                 /* Check PVD ID. */
  81                 if (pvd[0] !=  1  || pvd[1] != 'C' || pvd[2] != 'D' ||
  82                    pvd[3] != '0' || pvd[4] != '0' || pvd[5] != '1' ||
  83                    pvd[6] != 1 ||
  84                    strncmp(pvd + 40, "MINIX", 5) != 0) {
  85                         continue;
  86                 }
  87
  88                 /* 3. Both cXdYp1 and p2 should have a superblock. */
  89                 found= 1;       /* Assume everything is okay */
  90                 for (minor = 1; minor <= 2; minor++) {
  91                         name2[8]= '0' + probelist[disk];
  92                         name2[10]= '0' + minor;
  93
  94                         fd = open(name2, O_RDONLY);
  95                         if (fd < 0)
  96                         {
  97                                 if (errno != ENXIO)
  98                                 {
  99                                         fprintf(stderr,
 100                                                 "open '%s' failed: %s\n",
 101                                                 name2, strerror(errno));
 102                                 }
 103                                 found= 0;
 104                                 break;
 105                         }
 106                         r = read(fd, pvd, sizeof(pvd));
 107                         if (r != sizeof(pvd))
 108                         {
 109                                 fprintf(stderr,
 110                                 "error reading super block from '%s': %s\n",
 111                                         name2, strerror(errno));
 112                                 close(fd);
 113                                 found= 0;
 114                                 break;
 115                         }
 116                         close(fd);
 117
 118                         magicp= (u16_t *)&pvd[SUPER_OFF+MAGIC_OFF];
 119                         if (*magicp != SUPER_V3)
 120                         {
 121                                 fprintf(stderr, "bad super block on %s\n",
 122                                         name2);
 123                                 found= 0;
 124                                 break;
 125                         }
 126                 }
 127
 128                 if (found)
 129                 {
 130                         fprintf(stderr, "\nFound.\n");
 131                         printf("%s\n", name1);
 132                         exit(0);
 133                 }
 134            }
 135         }
 136         fprintf(stderr, "\nNot found.\n");
 137
 138         return 1;
 139 }
 140