File: clear_console.c

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/*
Copyright (C) 2006-2019 Canonical Ltd.

clear_console and it's man page are free software; you can redistribute it
and/or modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2, or (at your
option) any later version.
*/

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <string.h>
#include <getopt.h>
#include <errno.h>
#include <unistd.h>
#include <sys/ioctl.h>
#if defined(__linux)
#include <linux/kd.h>
#include <linux/vt.h>
#elif defined(__FreeBSD_kernel__)
#include <sys/consio.h>
#include <sys/kbio.h>
#endif

#include <curses.h>
#include <term.h>

#define VERSION "0.1"

char* progname;
int quiet = 0;

void usage()
{
  fprintf(stderr, "Usage: %s [option]\n", progname);
  fprintf(stderr, "valid options are:\n");
  fprintf(stderr, "\t-q  --quiet    don't print error messages\n");
  fprintf(stderr, "\t-h --help      display this help text and exit\n");
  fprintf(stderr, "\t-V --version   display version information and exit\n");
}

const struct option opts[] =
{
  /* operations */
    {"help", no_argument, 0, 'h'},
    {"version", no_argument, 0, 'V'},
    {"quiet", no_argument, 0, 'q'},
    {0, 0, 0, 0}
};

static int putch(int c)
{
        return putchar(c);
}


/* taken from console-utils, lib/misc-console-utils.c */

int is_a_console(int fd)
{
#if defined(__linux__)
  char arg;
#elif defined(__FreeBSD_kernel__)
  int arg;
#endif

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

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

  /* try read-only */
  fd = open(fnam, O_RDWR);

  /* if failed, try read-only */
  if (fd < 0 && errno == EACCES)
      fd = open(fnam, O_RDONLY);

  /* if failed, try write-only */
  if (fd < 0 && errno == EACCES)
      fd = open(fnam, O_WRONLY);

  /* if failed, fail */
  if (fd < 0)
      return -1;

  /* if not a console, fail */
  if (! is_a_console(fd))
    {
      close(fd);
      return -1;
    }

  /* success */
  return fd;
}

/*
 * 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).
 *
 * if tty_name is non-NULL, try this one instead.
 */

int get_console_fd(char* tty_name)
{
  int fd;

  if (tty_name)
    {
      if (-1 == (fd = open_a_console(tty_name)))
        return -1;
      else
        return fd;
    }

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

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

#if 0
  fprintf(stderr,
          _("Couldnt get a file descriptor referring to the console\n"));
#endif
  return -1;            /* total failure */
}


int is_pseudo_tty(int fd)
{
  char *tty = ttyname(fd);

  if (!tty)
    {
      if (!quiet)
	perror("ttyname");
      return 0;
    }

  if (strlen(tty) >= 9 && !strncmp(tty, "/dev/pts/", 9))
    return 1;

  if (strlen(tty) >= 8 && !strncmp(tty, "/dev/tty", 8)
      && tty[8] >= 'a' && tty[8] <= 'z')
    return 1;

  return 0;
}

int clear_console(int fd)
{
  int num, tmp_num;
#if defined(__linux__)
  struct vt_stat vtstat;
#endif

  /* Linux console secure erase (since 2.6.39), this is sufficient there;
     other terminals silently ignore this code.  If they don't and write junk
     instead, well, we're clearing the screen anyway.
   */ 
  write(1, "\e[3J", 4);

  /* clear screen */
  setupterm((char *) 0, 1, (int *) 0);
  if (tputs(clear_screen, lines > 0 ? lines : 1, putch) == ERR)
    {
      exit(1);
    }

  if (is_pseudo_tty(STDIN_FILENO))
    return 0;

  if (!strcmp(getenv("TERM"), "screen"))
      return 0;

  /* get current vt */
#if defined(__linux__)
  if (ioctl(fd, VT_GETSTATE, &vtstat) < 0)
#elif defined(__FreeBSD_kernel__)
  if (ioctl(fd, VT_ACTIVATE, &num) < 0)
#endif
    {
      if (!quiet)
	fprintf(stderr, "%s: cannot get VTstate\n", progname);
      exit(1);
    }
#if defined(__linux__)
  num = vtstat.v_active;
#endif
  tmp_num = (num == 6 ? 5 : 6);

  /* switch vt to clear the scrollback buffer */
  if (ioctl(fd, VT_ACTIVATE, tmp_num))
    {
      if (!quiet)
	perror("chvt: VT_ACTIVATE");
      exit(1);
    }

  if (ioctl(fd, VT_WAITACTIVE, tmp_num))
    {
      if (!quiet)
	perror("VT_WAITACTIVE");
      exit(1);
    }

  /* switch back */
  if (ioctl(fd, VT_ACTIVATE, num))
    {
      if (!quiet)
	perror("chvt: VT_ACTIVATE");
      exit(1);
    }

  if (ioctl(fd, VT_WAITACTIVE, num))
    {
      if (!quiet)
	perror("VT_WAITACTIVE");
      exit(1);
    }
  return 0;
}

int main (int argc, char* argv[])
{
  int fd;
  int result;                          /* option handling */
  int an_option;

  if ((progname = strrchr(argv[0], '/')) == NULL)
    progname = argv[0];
  else
    progname++;

  while (1)
    {
      result = getopt_long(argc, argv, "Vhq", opts, &an_option);
      
      if (result == EOF)
	break;

      switch (result)
        {
        case 'V':
	  fprintf(stdout, "%s: Version %s\n", progname, VERSION);
          exit (0);
        case 'h':
          usage();
          exit (0);
	  
        case 'q':
          quiet = 1;
        }
    }

  if (optind < argc)
    {
      if (!quiet)
	fprintf(stderr, "%s: no non-option arguments are valid", progname);
      exit(1);
    }

  if ((fd = get_console_fd(NULL)) == -1)
    {
      if (!quiet)
	fprintf(stderr, "%s: terminal is not a console\n", progname);
      exit(1);
    }

  clear_console(fd);

  return 0;
}