From: Brad Boyer Subject: Re: [PATCH 3/3] Add timeout feature Date: Tue, 8 Jul 2008 21:21:47 -0700 Message-ID: <20080709042147.GB20695@cynthia.pants.nu> References: <20080630212450t-sato@mail.jp.nec.com> <20080701081026.GB16691@infradead.org> <20080707110730.GG5643@ucw.cz> <20080708231026.GP11558@disturbed> <20080708232031.GE18195@elf.ucw.cz> <20080709005254.GQ11558@disturbed> <20080709010922.GE9957@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: Theodore Tso , Pavel Machek , Christoph Hellwig , Takashi Sato , akpm@linux-foundation.org, viro@ZenIV.linux.org Return-path: Received: from [76.245.85.235] ([76.245.85.235]:59050 "EHLO cynthia.pants.nu" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1754985AbYGIFva (ORCPT ); Wed, 9 Jul 2008 01:51:30 -0400 Content-Disposition: inline In-Reply-To: <20080709010922.GE9957@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Jul 08, 2008 at 09:09:22PM -0400, Theodore Tso wrote: > I had argued for the timeout (and so it's mostly my fault that > Takashi-San included it as a feature) mainly because I was (and still > amm) deeply paranoid about the competence of the application > programers who might use this feature. I could see them screwing up > leaving it locked forever --- perhaps when their program core dumps or > when the user types ^C and they forgot to install a signal handler, > leaving the filesystem frozen forever. > > In the meantime, user applications that try to create files on that > filesystem, or write to files already opened when the filesystem are > frozen will accumulate dirty pages in the page cache, until the system > finally falls over. > > Think about some of the evil perpetrated by hal and the userspace > suspend-resume scripts (and how much complexity with random XML > fragments getting parsed by various dbus plugins), and tell me with a > straight face that you would trust these modern-day desktop > application writers with this interface. Because they *will* find > some interesting way to (ab)use it..... > > Also, I didn't think the extra code complexity to implements timeouts > was *that* bad --- it seemed fairly small for the functionality. Just as an extra point of reference, VxFS supports a freeze/thaw by ioctl very similar to this including a timeout in seconds. This means someone else thought it was a useful feature. http://sfdoccentral.symantec.com/sf/5.0/linux/manpages/vxfs/vxfsio_7.html Brad Boyer flar@allandria.com