Re: [RFC]: d-i, /dev, busybox

[Erik Andersen <andersen@codepoet.org>]

On Mon Feb 12, 2001 at 08:25:15PM -0800, David Whedon wrote:
> My goal is to make debian-installer create the files in /dev on boot, and I
> would also like to use busybox's linuxrc-init-inittab feature because it is
> clean and fairly standard.  There are a couple ways we can do this, all have
> drawbacks, I know this is a solved problem so I'm looking for advice, someone to
> poitn out something I missed.
> 
> I've gotten Methods A and B to work so there aren't any hidden problems with
> them as far as I know.

Is the goal to end up with a ramdisk that contains the installer?
How about the following variant on A:

    * boot with load_ramdisk=1 initrd=debian.gz root=/dev/ram0

    * kernel loads debian.gz initrd into mem and mounts it
	initrd contains the installer initrd, with a mimimal 
	set of devices in /dev, just in case...
	    null  ram@  ram0  ram1  tty  tty1  zero

    * /linuxrc runs and looks something like the following:

	#!/bin/sh
	# Yet another mess by Erik Andersen <andersee@debian.org>

	# Build ramdisks to overlay the underlying filesystem
	# This allows the underlying filesystem to not need
	# a zillion inodes so less space gets wasted.
	echo -n "Building ramdisk: "

	# fit /dev/* inodes into 96k (leaves 6k free w/1041 devices)
	dd if=/dev/zero of=/dev/ram1 bs=1k count=96
	/sbin/mkfs.minix -n30 -i 1200 /dev/ram1 96
	mount /dev/ram1 /mnt -t minix -o rw

	# copy what few /dev entries we have into the ramdisk
	cp -a /dev/* /mnt
	umount /dev/ram1

	# Now overlay our ramdisk onto /dev
	mount /dev/ram1 /dev -t minix -o rw

	# create all the device special file nodes we need in /dev
	/etc/init.d/makedevs

    * /linuxrc exits

    * Kernel mounts up /, but since we told the kernel
    at boot time that / is /dev/ram0, well and lo and 
    behold, sitting on /dev/ram0 is the initrd that just ran.  
    The kernel doesn't care, it mounts it up as usual.
    /dev/ram1 is is still mounted on /dev 

    * /sbin/init runs and finds /dev fully populated.

Feel free to adjust the basic recipe to taste...

 -Erik

--
Erik B. Andersen   email:  andersee@debian.org, andersen@lineo.com
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