Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 21 Mar 2003 03:57:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 21 Mar 2003 03:57:58 -0500 Received: from smtpzilla5.xs4all.nl ([194.109.127.141]:35602 "EHLO smtpzilla5.xs4all.nl") by vger.kernel.org with ESMTP id ; Fri, 21 Mar 2003 03:57:57 -0500 Date: Fri, 21 Mar 2003 10:08:43 +0100 (CET) From: Roman Zippel X-X-Sender: roman@serv To: Greg KH cc: Andries.Brouwer@cwi.nl, , Subject: Re: [PATCH] alternative dev patch In-Reply-To: <20030321012455.GB10298@kroah.com> Message-ID: References:

<20030321012455.GB10298@kroah.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2758 Lines: 61 Hi, On Thu, 20 Mar 2003, Greg KH wrote: > On Fri, Mar 21, 2003 at 12:03:57AM +0100, Roman Zippel wrote: > > I'm unsure how your code will scale. It depends on how that code will be > > used. If drivers register a lot of devices, your lookup function has to > > scan a possibly very long list of minor devices and that function is > > difficult to optimize. > > And then we grab the BKL :( This is currently required for either implementation and needs to be moved to the driver. > Hint, optimizing the open() path for char devices is not anything we > will probably be doing in 2.6, due to the BKL usage there. It's also > not anything anyone has seen on any known benchmarks as a point of > contention, so I would not really worry about this for now. The BKL also shouldn't be a reason to make it unnecessary expensive? I don't understand your argument. > > char devices don't have partitions, so you hardly need regions. The > > problem with the tty layer is that the console and the serial devices > > should have different majors. > > There are a number of char drivers that have "regions". The tty layer > support them, and the usb core supports them as two examples. I'm sure > there are others. Personally, I like the symmetry with the block device > function the way Andries did it. Every single call to usb_register_dev in 2.5.65 uses exactly 1 minor number. Block device drivers need regions because they have partitions and we need to find out which device a partition belongs to. Where have character devices such requirements? > > See the misc device example. It doesn't have a table, but the list is now > > only needed to generate /proc/misc. As soon as character devices are > > better integrated into the driver model, even this list is not needed > > anymore. This means for simple character devices, we can easily add a > > alloc_chardev/add_chardev interface similiar to block devices. > > No, I don't see /proc/misc going away due to the driver model, I imagine > there are too many users of it to disappear. Also, the driver model > doesn't care a thing about major/minor numbers so I don't understand how > you think it can help in this situation. I didn't mean that /proc/misc goes away, I meant the misc_list in misc.c. They could be other ways to generate /proc/misc. /proc/devices, /proc/misc, /proc/tty/drivers, ... is currently mostly needed to generate device nodes for dynamic device numbers. This badly needs a more generic mechanism. bye, Roman - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/