Bug#606806: initramfs-tools: Handling of numeric root= arguments is not udev-friendly

[maximilian attems <maks@stro.at>]

On Sat, Dec 11, 2010 at 01:14:42PM -0800, Evan Broder wrote:
> 
> If you pass a root= argument with a numeric device number
> (i.e. root=0806), that's currently resolved by running mknod to create
> a /dev/root device with an appropriate major/minor number and setting
> ROOT=/dev/root (the parse_numeric function in scripts/functions).
> 
> However, this /dev/root device is completely unknown to udev. On
> Ubuntu, this leads to problems because we use udev to wait for the
> root device to appear. Since /dev/root isn't in udev's database, the
> boot hangs forever (well, it hangs until rootdelay passes).
> 
> udev's standard configuration creates /dev/block/N:N symlinks for
> every block device in its database (see the first non-comment line of
> /lib/udev/rules.d/50-udev-default.rules). Setting ROOT to the
> /dev/block/N:N symlink instead of creating a new /dev/root device and
> setting ROOT to that solves Ubuntu's problem.
> 
> See https://bugs.launchpad.net/bugs/576429 for more discussion.
> 
> We've applied a patch (attached) to do this, and thought you might be
> interested in doing the same.
> 
> Thanks.

thank you for submitting, I had seen it and had a question to the patch.

> === modified file 'scripts/functions'
> --- scripts/functions	2010-10-04 22:34:10 +0000
> +++ scripts/functions	2010-11-27 02:56:12 +0000
> @@ -364,8 +364,8 @@
>  		return
>  		;;
>  	[0-9]*:[0-9]*)
> -		minor=${1#*:}
> -		major=${1%:*}
> +		minor=$(echo ${1#*:} | sed -e 's/^0*//')
> +		major=$(echo ${1%:*} | sed -e 's/^0*//')

I had wondered why you remove leading nulls, but now thanks
to your aboves desc I do not understand.

Now the trouble is the implementation, please use shell parameter
expansion. sed assumes busybox in the initramfs, which might not be
with the case with  BUSYBOX=no for small initramfs or mem constraint
boxes.  something like ${minor#0}, not sure if we need to account for more
then 2 prefixed zeroes, in this case shell guru's can give a hint.

>  		;;
>  	[A-Fa-f0-9]*)
>  		value=$(( 0x${1} ))
> @@ -377,8 +377,7 @@
>  		;;
>  	esac
>  
> -	mknod -m 600 /dev/root b ${major} ${minor}
> -	ROOT=/dev/root
> +	ROOT=/dev/block/${major}:${minor}
>  }
>  
>  # Parameter: device node to check

this assumes udev running in initramfs for the symlink.
together with devtmpfs and force loading one can built one without,
but I agree that this may now be very special case.
 

thank you for the feedback.

-- 
maks