linux-kernel - Re: No /dev/root with devtmpfs?

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Date:	Mon, 13 Feb 2012 10:48:30 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Kirill Smelkov <kirr@....spb.ru>
CC:	Paul Parsons <lost.distance@...oo.com>,
	Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org
Subject: Re: No /dev/root with devtmpfs?

On 02/13/2012 12:25 AM, Kirill Smelkov wrote:
>>
>> The bootloader might pass the root partition to the kernel via the
>> "root=" kernel parameter; these can be read at /proc/cmdline.
>> For example, on an HP iPAQ hx4700: root=/dev/mtdblock2
> 
> This does not work universally either, for example for
> 
>     root=PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF
> 
> 
> the kernel scans partitions and finds one for root by partition uuid
> (see name_to_dev_t() in init/do_mounts.c).
> 
> That's exactly my situation - I have universal flash image which can
> bee booted via CF slot (on several boards, thus will have different
> /dev/hd? or /dev/sd?) and via usb/cardreader (again different /dev/
> entry), and root is mounted by partition id.
> 
> The kernel has no problem finding root partition and mounting it. I just
> needed a sane and robust way to know its choice.
> 

In this case it's not the kernel, but the initramfs which does this
lookup.  In that case the initramfs could/should create /dev/root.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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