From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751657Ab0ESSF5 (ORCPT ); Wed, 19 May 2010 14:05:57 -0400 Received: from 0122700014.0.fullrate.dk ([95.166.99.235]:40114 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750709Ab0ESSF4 (ORCPT ); Wed, 19 May 2010 14:05:56 -0400 Date: Wed, 19 May 2010 20:05:54 +0200 From: Jens Axboe To: Linus Torvalds Cc: Miklos Szeredi , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org Subject: Re: [patch] pipe: add support for shrinking and growing pipes Message-ID: <20100519180554.GY25951@kernel.dk> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 19 2010, Linus Torvalds wrote: > > > On Wed, 19 May 2010, Miklos Szeredi wrote: > > > > One issue I see is that it's possible to grow pipes indefinitely. > > Should this be restricted to privileged users? > > Yes. But perhaps only if it grows past the default (or perhaps "default*2" > or similar). That way a normal user could shrink the pipe buffers, and > then grow them again if he wants to. That's still a bit arbitrary, I don't think allowing default*2 only for non-root is going to be hugely interesting. But limiting makes sense, but lets at least allow a larger max limit for the normal user. I'm suspecting that the media application that wants to use this will not be running as root, and we don't make the feature properly available to the ones that want to use it, then we may as well not do it. Or we could expose a sysctl for instance that holds the max non-root size. And make that default to default*16 or something. How does that sound? > Oh, and I think you need to also require that there be at least two > buffers. Otherwise we can't guarantee POSIX behavior, I think. Good point, and at least that part is easily doable :-) -- Jens Axboe