mount/mount_guess_rootdev.c

   1 /*
   2  * Having the wrong rootdevice listed in mtab is slightly inconvenient.
   3  * Try to guess what it could be...
   4  * In case /proc/cmdline exists, and has the format
   5  *      stuff root=R more stuff...
   6  * and we think we understand the number R, decode it as a root device.
   7  *
   8  * Another possibility:
   9  * Erik Andersen writes:
  10  *  I did a similar find_real_root_device_name() in busybox some time back.
  11  *  Basically, do a stat("/", &rootstat) then walk /dev stat'ing each file
  12  *  and if (statbuf.st_rdev == rootstat.st_rdev) then you have a match.
  13  *  Works fine.
  14  */
  15 #include <stdio.h>
  16 #include <string.h>
  17 #include "mount_guess_rootdev.h"
  18
  19 #define PROC_CMDLINE    "/proc/cmdline"
  20
  21 static char *
  22 rootdev(char *p) {
  23         unsigned long devno;
  24         char *ep;
  25         char *type = "hd";
  26         char let;
  27         int ma, mi;
  28         char devname[8];
  29
  30         devno = strtoul(p, &ep, 16);
  31         if ((ep == p+3 || ep == p+4) && (*ep == ' ' || *ep == 0)) {
  32                 ma = (devno >> 8);
  33                 mi = (devno & 0xff);
  34                 switch(ma) {
  35                 case 8:
  36                         type = "sd";
  37                         let = 'a'+(mi/16);
  38                         mi = mi%16;
  39                         break;
  40                 case 3:
  41                         let = 'a'; break;
  42                 case 0x16:
  43                         let = 'c'; break;
  44                 case 0x21:
  45                         let = 'e'; break;
  46                 case 0x22:
  47                         let = 'g'; break;
  48                 case 0x38:
  49                         let = 'i'; break;
  50                 case 0x39:
  51                         let = 'k'; break;
  52                 default:
  53                         return NULL;
  54                 }
  55                 if (mi & 0x40) {
  56                         mi -= 0x40;
  57                         let++;
  58                 }
  59                 if (mi == 0)
  60                         sprintf(devname, "/dev/%s%c", type, let);
  61                 else
  62                         sprintf(devname, "/dev/%s%c%d", type, let, mi);
  63                 return strdup(devname);
  64         }
  65         return NULL;
  66 }
  67
  68 char *
  69 mount_guess_rootdev() {
  70         FILE *cf;
  71         char line[1024];
  72         char *p;
  73
  74         cf = fopen(PROC_CMDLINE, "r");
  75         if (cf && fgets(line, sizeof(line), cf)) {
  76                 for (p = line; *p; p++)
  77                         if (!strncmp(p, " root=", 6))
  78                                 return rootdev(p+6);
  79         }
  80         return NULL;
  81 }
  82
  83 #if 0
  84 main(){
  85         char *p = mount_guess_rootdev();
  86         if (!p)
  87                 p = "/dev/root";
  88         printf("%s\n", p);
  89 }
  90 #endif