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getfd.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <linux/kd.h>
#include "nls.h"
#include "getfd.h"

/*
 * getfd.c
 *
 * Get an fd for use with kbd/console ioctls.
 * We try several things because opening /dev/console will fail
 * if someone else used X (which does a chown on /dev/console).
 */

static int
is_a_console(int fd) {
      char arg;

      arg = 0;
      return (ioctl(fd, KDGKBTYPE, &arg) == 0
            && ((arg == KB_101) || (arg == KB_84)));
}

static int
open_a_console(const char *fnam) {
      int fd;

      /*
       * For ioctl purposes we only need some fd and permissions
       * do not matter. But setfont:activatemap() does a write.
       */
      fd = open(fnam, O_RDWR);
      if (fd < 0 && errno == EACCES)
            fd = open(fnam, O_WRONLY);
      if (fd < 0 && errno == EACCES)
            fd = open(fnam, O_RDONLY);
      if (fd < 0)
            return -1;
      if (!is_a_console(fd)) {
            close(fd);
            return -1;
      }
      return fd;
}

int getfd(const char *fnam) {
      int fd;

      if (fnam) {
            fd = open_a_console(fnam);
            if (fd >= 0)
                  return fd;
            fprintf(stderr,
                  _("Couldnt open %s\n"), fnam);
            exit(1);
      }

      fd = open_a_console("/dev/tty");
      if (fd >= 0)
            return fd;

      fd = open_a_console("/dev/tty0");
      if (fd >= 0)
            return fd;

      fd = open_a_console("/dev/vc/0");
      if (fd >= 0)
            return fd;

      fd = open_a_console("/dev/console");
      if (fd >= 0)
            return fd;

      for (fd = 0; fd < 3; fd++)
            if (is_a_console(fd))
                  return fd;

      fprintf(stderr,
            _("Couldnt get a file descriptor referring to the console\n"));
      exit(1);          /* total failure */
}

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