linux-kernel - Re: [PATCH] fs: add FD_CLOFORK and O

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Message-ID: <1304745945.2821.601.camel@edumazet-laptop>
Date:	Sat, 07 May 2011 07:25:45 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Matthew Wilcox <matthew@....cx>, Arnd Bergmann <arnd@...db.de>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] fs: add FD_CLOFORK and O_CLOFORK

Le samedi 07 mai 2011 à 12:49 +0800, Changli Gao a écrit :
> If FD_CLOFORK is 1, when a fork occurs, the corresponding file descriptor
> will be closed for the child process. IOW, the file descriptor isn't
> inheritable.
> 
> FD_CLOFORK is used as IBM does.

Is it part of a standard, and what could be the use for such thing ?
Why had we wait 2011 to add it in linux ?

> 
> O_CLOFORK is also added to avoid the additional fcntl(2) after open(2).
> 
> Signed-off-by: Changli Gao <xiaosuo@...il.com>


Your implementation has some peformance implication.

close_on_exec and close_on_fork bit for a given fd would be on separate
cache lines. So you add a cost on threaded programs for open()/close()

[ Yes, we apparently clear close_on_exec bit in close()... we could let
it untouched and make flush_old_files() aware of that ]



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