Date: Mon, 11 May 1998 04:23:36 +0100 From: Brian Somers <brian@Awfulhak.org> To: freebsd-hackers@FreeBSD.ORG Subject: SCM_RIGHTS & session ids Message-ID: <199805110323.EAA28416@awfulhak.org>
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Hi,
I've bumped into a bit of a problem implementing multilink ppp.
Maybe someone can suggest a way out of my dilemma....
I have two processes, each of which has its own session id and is the
only process in the sessions only process group. I've closed STDOUT
and STDERR, and STDIN_FILENO is the only thing keeping the
controlling terminal attached. Both the process group and the session
id of each process is owned by its respective terminal.
.-------------. .-------------.
| Session 123 | | Session 456 |
`-------------' `-------------'
| |
.------------. .------------.
| /dev/cuaa0 | | /dev/cuaa1 |
`------------' `------------'
| |
.-------------. .-------------.
| Process 123 | | Process 456 |
`-------------' `-------------'
I wish to pass descriptor 0 from p123 to p456 using SCM_RIGHTS over a
unix domain socket, and then for p123 to exit.
When I do this, as soon as p456 selects on the passed descriptor (say
descriptor 10), and *after* p123 has exited, I get an exception from
select() (exception fdset) and the descriptor is useless.
If I have p123 close() STDIN_FILENO after the transfer, then
execl("/bin/sleep", "sleep", 100", NULL)
p456 can read descriptor 10 for 100 seconds - once (I assume) the
process group of /dev/cuaa0 is gone, all descriptors are invalidated.
What I've tried (nothing's helped):
o p123 does an fd = open(ttyname(STDIN_FILENO), O_RDWR), then
close(STDIN_FILENO) and pass fd to p456.
o p123 calls tcsetpgrp(STDIN_FILENO, 456) - doesn't work 'cos p456
isn't part of p123s session.
This all works when there are no controlling terminals involved (ppp
over tcp).
I guess that the problem is that a process group has only
one session and a session has only one controlling terminal...
Is the only way to simply exec() a keepalive process() (yeuch) ?
TIA.
--
Brian <brian@Awfulhak.org>, <brian@FreeBSD.org>, <brian@OpenBSD.org>
<http://www.Awfulhak.org>;
Don't _EVER_ lose your sense of humour....
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