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

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Date:	Tue, 19 Apr 2011 18:13:01 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Stas Sergeev <stsp@...et.ru>,
	Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [path][rfc] add PR_DETACH prctl command [3/3]

On 04/19, Alan Cox wrote:
>
> > 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 complicates this code.

> 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 !

... to add the non-portable (and _imho_ unneeded) feauture.

IOW, personally I do not like this change in any case. But I am not
going to argue if someone acks this new feauture.




I'll try to check these patches from the correctness pov tomorrow,
but to be honest I hope someone will nack them before I start ;)

Oleg.

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