glibc/sysdeps/unix/sysv/linux/ptsname.c

/* Copyright (C) 1998-2020 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Zack Weinberg <zack@rabi.phys.columbia.edu>, 1998.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <errno.h>
#include <paths.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <termios.h>
#include <unistd.h>

#include <_itoa.h>

/* Check if DEV corresponds to a master pseudo terminal device.  */
#define MASTER_P(Dev)							\
  (__gnu_dev_major ((Dev)) == 2						\
   || (__gnu_dev_major ((Dev)) == 4					\
       && __gnu_dev_minor ((Dev)) >= 128 && __gnu_dev_minor ((Dev)) < 192) \
   || (__gnu_dev_major ((Dev)) >= 128 && __gnu_dev_major ((Dev)) < 136))

/* Check if DEV corresponds to a slave pseudo terminal device.  */
#define SLAVE_P(Dev)							\
  (__gnu_dev_major ((Dev)) == 3						\
   || (__gnu_dev_major ((Dev)) == 4					\
       && __gnu_dev_minor ((Dev)) >= 192 && __gnu_dev_minor ((Dev)) < 256) \
   || (__gnu_dev_major ((Dev)) >= 136 && __gnu_dev_major ((Dev)) < 144))

/* Note that major number 4 corresponds to the old BSD style pseudo
   terminal devices.  As of Linux 2.1.115 these are no longer
   supported.  They have been replaced by major numbers 2 (masters)
   and 3 (slaves).  */

/* Directory where we can find the slave pty nodes.  */
#define _PATH_DEVPTS "/dev/pts/"

/* The are declared in getpt.c.  */
extern const char __libc_ptyname1[] attribute_hidden;
extern const char __libc_ptyname2[] attribute_hidden;

/* Static buffer for `ptsname'.  */
static char buffer[sizeof (_PATH_DEVPTS) + 20];


/* Return the pathname of the pseudo terminal slave associated with
   the master FD is open on, or NULL on errors.
   The returned storage is good until the next call to this function.  */
char *
ptsname (int fd)
{
  return __ptsname_r (fd, buffer, sizeof (buffer)) != 0 ? NULL : buffer;
}


int
__ptsname_internal (int fd, char *buf, size_t buflen, struct stat64 *stp)
{
  int save_errno = errno;
  unsigned int ptyno;

  if (!__isatty (fd))
    {
      __set_errno (ENOTTY);
      return ENOTTY;
    }

#ifdef TIOCGPTN
  if (__ioctl (fd, TIOCGPTN, &ptyno) == 0)
    {
      /* Buffer we use to print the number in.  For a maximum size for
	 `int' of 8 bytes we never need more than 20 digits.  */
      char numbuf[21];
      const char *devpts = _PATH_DEVPTS;
      const size_t devptslen = strlen (_PATH_DEVPTS);
      char *p;

      numbuf[sizeof (numbuf) - 1] = '\0';
      p = _itoa_word (ptyno, &numbuf[sizeof (numbuf) - 1], 10, 0);

      if (buflen < devptslen + (&numbuf[sizeof (numbuf)] - p))
	{
	  __set_errno (ERANGE);
	  return ERANGE;
	}

      memcpy (__stpcpy (buf, devpts), p, &numbuf[sizeof (numbuf)] - p);
    }
  else if (errno != EINVAL)
    return errno;
  else
#endif
    {
      char *p;

      if (buflen < strlen (_PATH_TTY) + 3)
	{
	  __set_errno (ERANGE);
	  return ERANGE;
	}

      if (__fxstat64 (_STAT_VER, fd, stp) < 0)
	return errno;

      /* Check if FD really is a master pseudo terminal.  */
      if (! MASTER_P (stp->st_rdev))
	{
	  __set_errno (ENOTTY);
	  return ENOTTY;
	}

      ptyno = __gnu_dev_minor (stp->st_rdev);

      if (ptyno / 16 >= strlen (__libc_ptyname1))
	{
	  __set_errno (ENOTTY);
	  return ENOTTY;
	}

      p = __stpcpy (buf, _PATH_TTY);
      p[0] = __libc_ptyname1[ptyno / 16];
      p[1] = __libc_ptyname2[ptyno % 16];
      p[2] = '\0';
    }

  if (__xstat64 (_STAT_VER, buf, stp) < 0)
    return errno;

  /* Check if the name we're about to return really corresponds to a
     slave pseudo terminal.  */
  if (! S_ISCHR (stp->st_mode) || ! SLAVE_P (stp->st_rdev))
    {
      /* This really is a configuration problem.  */
      __set_errno (ENOTTY);
      return ENOTTY;
    }

  __set_errno (save_errno);
  return 0;
}


/* Store at most BUFLEN characters of the pathname of the slave pseudo
   terminal associated with the master FD is open on in BUF.
   Return 0 on success, otherwise an error number.  */
int
__ptsname_r (int fd, char *buf, size_t buflen)
{
  struct stat64 st;
  return __ptsname_internal (fd, buf, buflen, &st);
}
weak_alias (__ptsname_r, ptsname_r)