linux-kernel - Re: [patch 7/8] fdmap v2

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Date:	Fri, 8 Jun 2007 08:07:46 -0400
From:	Theodore Tso <tytso@....edu>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Ulrich Drepper <drepper@...hat.com>,
	Eric Dumazet <dada1@...mosbay.com>,
	Kyle Moffett <mrmacman_g4@....com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 7/8] fdmap v2 - implement sys_socket2

On Thu, Jun 07, 2007 at 03:40:14PM -0700, Davide Libenzi wrote:
> Yes. Files with the CLOFORK and CLOEXEC flag do not count for fork and 
> exec copies.
> I was also planning on doing it in __put_unused_fd(), every time 
> fmap->count goes to zero. But get_random_int() is not as cheap as I 
> thought. If we use a cheaper (although less secure) function to mix pid & 
> jiffies, we could do it even in there.

Um, how cheap do you need it?  get_random_int() is actually pretty
cheep, since it was designed to be usable by the networking stack for
sequence numbers for TCP packets; and it's not like sys_close() or
sys_open() is a majorly critical path, is it?  If the concern is
increasing the potential hold time, I suppose you could have the
exactly two callers of __put_unused_fd() (sys_close() and
put_unused_fd()) call get_random_int() before grabbing the
current->files->file_lock spinlock,

						- Ted
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