linux-kernel - Re: [path][rfc] add PR_DETACH prctl command [3/3]

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Message-ID: <4DADA581.9060700@aknet.ru>
Date:	Tue, 19 Apr 2011 19:08:49 +0400
From:	Stas Sergeev <stsp@...et.ru>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Oleg Nesterov <oleg@...hat.com>,
	Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [path][rfc] add PR_DETACH prctl command [3/3]

19.04.2011 18:58, Alan Cox wrote:
>> The attached patch implements the PR_DETACH prctl
>> command. It detaches the entire process group from
>> its parent, allowing the parent to still read the detach
>> code with normal wait(). If the process then exits, the
>> notification of the new parent is delayed till the old parent
>> does either wait() to read the detach code, or exits.
> What is the use case for this and why won't existing process group
> interfaces do the job ?
The use case is to daemonize the process with threads.
You first need to detach it from its parent, then use TIOCNOTTY
ioctl to detach from the tty (TIOCNOTTY_GRP doesn't seem
to exist too, though, but might be easy to implement).
There are a few workarounds to that that I am aware of,
but what exactly interfaces do you have in mind? I have
found nothing that allows to do the same without a workarounds
like this:
https://lkml.org/lkml/2011/4/8/278
The current way of detaching, which is a fork/exit combo,
loses all threads, so, when you call daemon() and you had
threads, you are a toast.
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