Date: Wed, 13 Nov 1996 19:16:18 +1100 From: Bruce Evans <bde@zeta.org.au> To: hackers@freebsd.org, jkh@time.cdrom.com Subject: Re: Is our ASYNC I/O support for ttys broken? Message-ID: <199611130816.TAA28631@godzilla.zeta.org.au>
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>Thomas Roell over at X Inside just sent me this little snippet,
>complaining that ASYNC I/O was broken in FreeBSD where it worked with
>Linux and SVR4. Any comments?
The status hasn't changed since he complained a year or so ago.
SIGIO for ASYNC tty i/o is only sent to the process group of the tty,
and process group stuff is limited by it being POSIX conformant
with few extensions - the process group can not be changed using
F_SETOWN (although F_SETOWN takes you outside of POSIX) unless the
corresponding change using tcsetpgrp() would work. SIGIO for ASYNC
socket i/o works better because the process or process group of the
socket, and this is unrelated to the POSIX process group.
> fd = open("/dev/ttyd0", O_RDONLY | O_NONBLOCK);
>
> fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) | FASYNC);
> fcntl(fd, F_SETOWN, getpid());
The second fcntl is guaranteed to fail, since `fd' isn't a controlling
terminal. To make fd a controlling terminal, something like the following
must be done:
fork()
wait in parent, continue as follows in child:
setsid(); /* become a session leader with no ctty */
open as above
first fcntl as above
ioctl(fd, TIOCSCTTY, NULL); /* make fd the ctty */
second fcntl as above
Bruce
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