From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olof Johansson Subject: Re: [PATCH v3] mmc: add config and runtime option for number of mmcblk minors Date: Wed, 8 Sep 2010 10:57:21 -0500 Message-ID: <20100908155721.GD23745@lixom.net> References: <20100818041333.GA14149@lixom.net> <20100818171636.0625b668.akpm@linux-foundation.org> <20100819032230.GA21980@lixom.net> <20100820010242.GA29588@lixom.net> <20100820221323.GC8535@lixom.net> <20100908145705.GC23745@lixom.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail.lixom.net ([70.86.134.90]:45561 "EHLO mail.lixom.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755950Ab0IHP5W (ORCPT ); Wed, 8 Sep 2010 11:57:22 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Kay Sievers Cc: Lei Wen , Andrew Morton , linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org, Mandeep Baines On Wed, Sep 08, 2010 at 05:19:25PM +0200, Kay Sievers wrote: > On Wed, Sep 8, 2010 at 16:57, Olof Johansson wrote: > > On Wed, Sep 08, 2010 at 10:25:58PM +0800, Lei Wen wrote: > > > >> The patch's purpose is good. As modern sd&mmc is used to host the file > >> system, the 8 partition limitation is becoming a kind of bottleneck... > >> But why not just add GENHD_FL_EXT_DEVT flag to allow mmc use extended > >> partition numbers? > > > > No need to quote the whole patch next time. :) > > > > Given that MMC is sometimes used in deeply embedded environments where > > udev might not be running to take care of dynamic device numbering, > > I chose to stay with a static layout. > > > > I could be convinced otherwise though. It would cause some additional > > hassles for me since we start udev lateish during boot and have a > > prepopulated /dev before that, but that can be dealt with. > > I think the extended number are only used for stuff larger than the static 8? Ah, yes, of course. > Apart from that, you can not reliably or securely use a static /dev > these days, you never know which device you talk to, because the > kernel has far too many dynamically assigned numbers. For that reason, > most embedded setups use the busybox hack to populate /dev. Recent > kernels have a devfs again, and there is no reason today to continue > any static /dev experiments -- unless someone is going over the entire > tree and fixes all the dynamic assignments, which is unlikely to > happen ever. Yeah, it's a weak argument but I wanted to go for the least surprising one for anyone who still relies on static numbering of mmc, since it's used as root device, etc. But with the first 8 minors being the same as before, there's little reason to care about that -- the EXT_DEVT approach will actually be the smaller change, since it won't renumber anything, just extend in a different part of the address space. Lei, want to submit a proper patch for it to replace mine? -Olof