support/support_openpty.c

   1 /* Open a pseudoterminal.
   2    Copyright (C) 2018-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <support/tty.h>
  20 #include <support/check.h>
  21 #include <support/support.h>
  22
  23 #include <errno.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26
  27 #include <fcntl.h>
  28 #include <termios.h>
  29 #include <sys/ioctl.h>
  30 #include <unistd.h>
  31
  32 /* As ptsname, but allocates space for an appropriately-sized string
  33    using malloc.  */
  34 static char *
  35 xptsname (int fd)
  36 {
  37   int rv;
  38   size_t buf_len = 128;
  39   char *buf = xmalloc (buf_len);
  40   for (;;)
  41     {
  42       rv = ptsname_r (fd, buf, buf_len);
  43       if (rv)
  44         FAIL_EXIT1 ("ptsname_r: %s", strerror (errno));
  45
  46       if (memchr (buf, '\0', buf_len))
  47         return buf; /* ptsname succeeded and the buffer was not truncated */
  48
  49       buf_len *= 2;
  50       buf = xrealloc (buf, buf_len);
  51     }
  52 }
  53
  54 void
  55 support_openpty (int *a_outer, int *a_inner, char **a_name,
  56                  const struct termios *termp,
  57                  const struct winsize *winp)
  58 {
  59   int outer = -1, inner = -1;
  60   char *namebuf = 0;
  61
  62   outer = posix_openpt (O_RDWR | O_NOCTTY);
  63   if (outer == -1)
  64     FAIL_EXIT1 ("posix_openpt: %s", strerror (errno));
  65
  66   if (grantpt (outer))
  67     FAIL_EXIT1 ("grantpt: %s", strerror (errno));
  68
  69   if (unlockpt (outer))
  70     FAIL_EXIT1 ("unlockpt: %s", strerror (errno));
  71
  72
  73 #ifdef TIOCGPTPEER
  74   inner = ioctl (outer, TIOCGPTPEER, O_RDWR | O_NOCTTY);
  75 #endif
  76   if (inner == -1)
  77     {
  78       /* The kernel might not support TIOCGPTPEER, fall back to open
  79          by name.  */
  80       namebuf = xptsname (outer);
  81       inner = open (namebuf, O_RDWR | O_NOCTTY);
  82       if (inner == -1)
  83         FAIL_EXIT1 ("%s: %s", namebuf, strerror (errno));
  84     }
  85
  86   if (termp)
  87     {
  88       if (tcsetattr (inner, TCSAFLUSH, termp))
  89         FAIL_EXIT1 ("tcsetattr: %s", strerror (errno));
  90     }
  91 #ifdef TIOCSWINSZ
  92   if (winp)
  93     {
  94       if (ioctl (inner, TIOCSWINSZ, winp))
  95         FAIL_EXIT1 ("TIOCSWINSZ: %s", strerror (errno));
  96     }
  97 #endif
  98
  99   if (a_name)
 100     {
 101       if (!namebuf)
 102         namebuf = xptsname (outer);
 103       *a_name = namebuf;
 104     }
 105   else
 106     free (namebuf);
 107   *a_outer = outer;
 108   *a_inner = inner;
 109 }