lib/util/openpty.c

   1 /*
   2  * openpty() tries to open a pty; applications won't have to
   3  * duplicate this code all the time (or change it if the system
   4  * pty interface changes).
   5  *
   6  * First version by Ben Gras <beng@few.vu.nl>,
   7  * Initially heavily based on telnetd/pty.c
   8  * by Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>.
   9  *
  10  */
  11 #include <libutil.h>
  12 #include <termios.h>
  13 #include <fcntl.h>
  14 #include <grp.h>
  15 #include <string.h>
  16 #include <stdlib.h>
  17 #include <errno.h>
  18 #include <stdio.h>
  19 #include <unistd.h>
  20 #include <sys/types.h>
  21 #include <sys/stat.h>
  22 #include <sys/ioc_tty.h>
  23
  24 #define DEV_DIR         "/dev"
  25
  26 /*
  27  * Allocate a PTY, by trying to open one repeatedly.
  28  */
  29 int openpty(int *amaster, int *aslave, char *name,
  30         struct termios *termp, struct winsize *winp)
  31 {
  32   char buff[128], temp[128];
  33   register int i, j;
  34   int pty_fd = -1, gr;
  35   static char tty_name[128];
  36   struct group *ttygroup;
  37   gid_t tty_gid = 0;
  38
  39   if(!amaster || !aslave) {
  40         errno = EINVAL;
  41         return -1;
  42   }
  43
  44   for(i = 'p'; i < 'w'; i++) {
  45         j = 0;
  46         do {
  47                 sprintf(buff, "%s/pty%c%c",
  48                         DEV_DIR, i, (j < 10) ? j + '0' : j + 'a' - 10);
  49
  50                 if((*amaster = open(buff, O_RDWR)) >= 0) {
  51                   sprintf(tty_name, "%s/tty%c%c", DEV_DIR,
  52                         i, (j < 10) ? j + '0' : j + 'a' - 10);
  53                   if((*aslave = open(tty_name, O_RDWR)) >= 0)
  54                         break;
  55                 }
  56                 close(*amaster);
  57
  58                 j++;
  59                 if (j == 16) break;
  60         } while(1);
  61
  62         /* Did we find one? */
  63         if (j < 16) break;
  64   }
  65   if (*amaster < 0) { errno = ENOENT; return(-1); }
  66
  67   setgrent();
  68   ttygroup = getgrnam("tty");
  69   endgrent();
  70   if(ttygroup) tty_gid = ttygroup->gr_gid;
  71
  72   if(name) strcpy(name, tty_name);
  73
  74   /* Ignore errors on these. */
  75   chown(tty_name, getuid(), tty_gid);
  76   chmod(tty_name, 0620);        /* -rw--w---- */
  77   if(termp) tcsetattr(*aslave, TCSAFLUSH, termp);
  78   if(winp) ioctl(*aslave, TIOCSWINSZ, winp);
  79
  80   return(0);
  81 }
  82