From: "Miquel van Smoorenburg" <miquels@cistron.nl>
Subject: Re: /dev/root: which approach ? [PATCH]
Date: Wed, 10 Mar 2004 20:18:52 +0000 (UTC)
Organization: Cistron Group
Message-ID: <c2nt7c$r32$1@news.cistron.nl>
References: <20040310162003.GA25688@cistron.nl> <20040310120145.248ae62d.akpm@osdl.org>
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Originator: miquels@cistron-office.nl (Miquel van Smoorenburg)
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In article <20040310120145.248ae62d.akpm@osdl.org>,
Andrew Morton  <akpm@osdl.org> wrote:
>Miquel van Smoorenburg <miquels@cistron.nl> wrote:
>>
>> Currently if you boot from a blockdevice with a dynamically
>> allocated major number (such as LVM or partitionable raid),
>> there is no way to check the root filesystem. The root
>> fs is still read-only, so you cannot create a device node
>> anywhere to point fsck at.
>> 
>> This was discussed on the linux-raid mailinglist, and I proposed
>> (as proof of concept) a simple check in bdget() to see if the
>> device is being opened is the /dev/root node and if so redirect
>> it to the current root device. This is a 8-line patch, the only
>> disadvantage I can think of is that for an open file, inode->i_rdev
>> is then different from blockdevice->bd_dev.
>
>The /dev/root alias resolution looks nice to me, which probably means that
>it has a fatal flaw.
>
>Is it not possible to create a device node on ramfs or ramdisk and point
>fsck at that?

Yes, I thought of that too. But that wouldn't be trivial for
existing installations, unless you're the maintainer of the
distributions init package. Oh wait .. ;)

Anyway, it seemed to me to be very useful, and since /proc/mounts
already refers to /dev/root it seemed to fit in naturally hence
the proposed patches. If the definitive answer is "do it in
userspace" then that's OK too.

Mike.

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