misc/kbd/getfd.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <unistd.h>
   4 #include <fcntl.h>
   5 #include <errno.h>
   6 #include <sys/ioctl.h>
   7 #include <linux/kd.h>
   8 #include "getfd.h"
   9
  10 /*
  11  * getfd.c
  12  *
  13  * Get an fd for use with kbd/console ioctls.
  14  * We try several things because opening /dev/console will fail
  15  * if someone else used X (which does a chown on /dev/console).
  16  */
  17
  18 static int
  19 is_a_console(int fd) {
  20         char arg;
  21
  22         arg = 0;
  23         return (ioctl(fd, KDGKBTYPE, &arg) == 0
  24                 && ((arg == KB_101) || (arg == KB_84)));
  25 }
  26
  27 static int
  28 open_a_console(const char *fnam) {
  29         int fd;
  30
  31         /*
  32          * For ioctl purposes we only need some fd and permissions
  33          * do not matter. But setfont:activatemap() does a write.
  34          */
  35         fd = open(fnam, O_RDWR);
  36         if (fd < 0 && errno == EACCES)
  37                 fd = open(fnam, O_WRONLY);
  38         if (fd < 0 && errno == EACCES)
  39                 fd = open(fnam, O_RDONLY);
  40         if (fd < 0)
  41                 return -1;
  42         if (!is_a_console(fd)) {
  43                 close(fd);
  44                 return -1;
  45         }
  46         return fd;
  47 }
  48
  49 int getfd(const char *fnam) {
  50         int fd;
  51
  52         if (fnam) {
  53                 fd = open_a_console(fnam);
  54                 if (fd >= 0)
  55                         return fd;
  56                 fprintf(stderr, "Couldnt open %s\n", fnam);
  57                 exit(1);
  58         }
  59
  60         fd = open_a_console("/dev/tty");
  61         if (fd >= 0)
  62                 return fd;
  63
  64         fd = open_a_console("/dev/tty0");
  65         if (fd >= 0)
  66                 return fd;
  67
  68         fd = open_a_console("/dev/vc/0");
  69         if (fd >= 0)
  70                 return fd;
  71
  72         fd = open_a_console("/dev/console");
  73         if (fd >= 0)
  74                 return fd;
  75
  76         for (fd = 0; fd < 3; fd++)
  77                 if (is_a_console(fd))
  78                         return fd;
  79
  80         fprintf(stderr, "Couldnt get a file descriptor referring to the console\n");
  81         exit(1);                /* total failure */
  82 }