Date: Wed, 13 Nov 1996 08:03:45 -0700 (MST) From: Thomas Roell <roell@crab.xinside.com> To: Bruce Evans <bde@zeta.org.au> Cc: hackers@freebsd.org, jkh@time.cdrom.com Subject: Re: Is our ASYNC I/O support for ttys broken? Message-ID: <199611131503.IAA09278@xeno.xinside.com> In-Reply-To: <199611130816.TAA28631@godzilla.zeta.org.au> References: <199611130816.TAA28631@godzilla.zeta.org.au>
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In your message of 13 November 1996 you write:
> >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.
Would it be possible to change that behaviour in the future ?
> > 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
Tried that already. Doesn't work.
Problem is that I really don't want to spawn subprocesses for
io-stuff. On the other hand asynchronous input is really mandatory if
you have a heavily loaded box and run CDE and/or OpenGL/PEX apps.
- Thomas
--
Denver Office THOMAS ROELL /\ Das Reh springt hoch,
+1(303)298-7478 X INSIDE INC / \/\ das Reh springt weit,
1801 Broadway, Suite 1710 / \ \/\ was soll es tun,
Denver, CO 80202 roell@xinside.com / Oelch! \ \ es hat ja Zeit.
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