linux-kernel - Re: [PATCH v3] mmc: add config and runtime option for number of mmcblk minors

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Date:	Wed, 8 Sep 2010 09:48:46 -0700
From:	Colin Cross <ccross@...gle.com>
To:	Olof Johansson <olof@...om.net>
Cc:	Kay Sievers <kay.sievers@...y.org>,
	Lei Wen <adrian.wenl@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mandeep Baines <msb@...omium.org>
Subject: Re: [PATCH v3] mmc: add config and runtime option for number of
 mmcblk minors

On Wed, Sep 8, 2010 at 8:57 AM, Olof Johansson <olof@...om.net> wrote:
> On Wed, Sep 08, 2010 at 05:19:25PM +0200, Kay Sievers wrote:
>> On Wed, Sep 8, 2010 at 16:57, Olof Johansson <olof@...om.net> 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?

I have a tested patch for this.  It also cleans up the connection
between devidx and minor numbers.  I'll send it shortly.
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