From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755689AbYH1Rlf (ORCPT ); Thu, 28 Aug 2008 13:41:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753624AbYH1RlN (ORCPT ); Thu, 28 Aug 2008 13:41:13 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:57857 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753427AbYH1RlM (ORCPT ); Thu, 28 Aug 2008 13:41:12 -0400 Date: Thu, 28 Aug 2008 10:38:13 -0700 From: Greg KH To: Tejun Heo Cc: Andrew Morton , Linux Kernel Mailing List Subject: Re: [PATCH RESEND] char_dev: add cdev->release() and convert cdev_alloc() to use it Message-ID: <20080828173813.GC18097@kroah.com> References: <48B6D428.2020308@kernel.org> <20080828164741.GA17475@kroah.com> <48B6D8D0.6080506@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <48B6D8D0.6080506@kernel.org> User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 28, 2008 at 06:56:48PM +0200, Tejun Heo wrote: > Greg KH wrote: > > Ick, I really don't want struct cdev to be used for lifecycle > > management, as it is only for major:minor stuff. Why do you want to > > make this change? > > Well, as cdev can be referenced from userspace, ->release is required > for most purposes. The reason why devices have been getting by without > it is because most chardevs are created on module load and destroyed on > module unload and in the meantime cdev refcount virtually equals module > refcnt, but I'm fairly sure we have cases where cdev can be destroyed > for other reasons then module unloading and it's very likely those cases > are buggy in the current code (backing structure gone bug cdev still > hanging around). Hm, I thought Al covered that when he created the cdev interface, I would be a bit supprised if this was the case. > As CUSE can create and destroy devices regardless of module reference > count, it falls in the second category and needs cdev->release() to make > sure the backing structure doesn't go away till cdev is released. But CUSE should be it's own module, right? And it would "own" the cdev, so the module and cdev count should be fine and matching. The userspace code could go away but the CUSE code should handle that with a different reference count. This is the way that hardware drivers handle the issue. thanks, greg k-h