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

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Message-ID: <20110419165429.71cb1508@lxorguk.ukuu.org.uk>
Date:	Tue, 19 Apr 2011 16:54:29 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Stas Sergeev <stsp@...et.ru>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [path][rfc] add PR_DETACH prctl command [3/3]

> 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.

Yes - you need to detach then create the threads.

The reason I ask is you appear to add overhead to various hot paths and
you add 48 bytes to each task struct if I read the code right. Thats half
a megabyte on a server running a pile of java gunge !

Alan
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