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From: Fred_Smith@computrition.com
To: egor duda <cygwin@cygwin.com>
Message-ID: <85256C66.00616DDA.00@cinote.computrition.com>
Date: Sun, 3 Nov 2002 12:44:28 -0500
Subject: Re: trouble using a PTY
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Egor:

Thanks for the info!

Fred


egor duda <deo@logos-m.ru> on 11/03/2002 09:47:53 AM

Please respond to egor duda <cygwin@cygwin.com>

To:   Fred Smith/Computrition
cc:   cygwin@cygwin.com
Subject:  Re: trouble using a PTY


Hi!
Sunday, 03 November, 2002 Fred_Smith@computrition.com
Fred_Smith@computrition.com wrote:
Fcc> I'm trying to run some very simple code that uses ptys. The
Fcc> code is from W. Richard Stevens APUE book. The only change is
This code is non-portable. The names of ptys are system-specific, and
not guaranteed to be named /dev/ptyXY.
On cygwin, master side of pseudo tty can be opened via
open("/dev/ptym",...). Then you can use grantpt(), unlockpt() and
ptsname() functions to access a slave side of pty.
Unfortunately, its not very portable, either. Proposed portable
interface to open master side of pseudo tty is posix_openpt(), but it
haven't been implemented on cygwin yet. "Patches are gratefully
accepted" (tm).
BTW, implementing this function looks like an easy prey for those who
wish to contribute something to cygwin, but afraid of complexities of
cygwin internals.
Fcc> the printf you see below. In this routine:
Fcc> int
Fcc> ptym_open(char *pts_name)
Fcc> {
Fcc>         int             fdm;
Fcc>         char    *ptr1, *ptr2;
Fcc>         strcpy(pts_name, "/dev/ptyXY");
Fcc>           /* array index: 0123456789 (for references in following
code) */
Fcc>         for (ptr1 = "pqrstuvwxyzPQRST"; *ptr1 != 0; ptr1++) {
Fcc>                 pts_name[8] = *ptr1;
Fcc>                 for (ptr2 = "0123456789abcdef"; *ptr2 != 0; ptr2++) {
Fcc>                         pts_name[9] = *ptr2;
Fcc>                         /* try to open master */
Fcc>                         if ( (fdm = open(pts_name, O_RDWR)) < 0) {
Fcc> printf ("ptym_open, open returned errno of: %d, pts_name=%s\n",
Fcc> errno,pts_name);
Fcc>                                 if (errno == ENOENT)    /* different
from
Fcc> EIO */
Fcc>                                         return(-1);   /*out of pty
devices
Fcc> */
Fcc>                                 else
Fcc>                                         continue;    /*try next pty
device
Fcc> */
Fcc>                        }
Fcc>                         pts_name[5] = 't';      /* change "pty" to
"tty" */
Fcc>                         return(fdm);            /* got it, return fd
of
Fcc> master */
Fcc>                 }
Fcc>         }
Fcc>         printf ("pty, at end, errno is: %d\n", errno);
Fcc>         return(-1);             /* out of pty devices */
Fcc> }
Fcc> the first call to open() fails, and the printf produces:
Fcc>      ptym_open, open returned errno of: 2, pts_name=/dev/ptyp0
Fcc> As far as I can deduce by reading cygwin docs and mailing list
archives,
Fcc> PTYs would be expected to work.
Fcc> I'd appreciate it if someone could point me in the right direction
here.
Fcc> attached is output of "cygcheck -s"
Egor.            mailto:deo@logos-m.ru ICQ 5165414 FidoNet 2:5020/496.19


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