Re: Kernel Firmware Loading

["Alexander E. Patrakov" <patrakov@ums.usu.ru>]

Andrew Benton wrote:

> If I wanted to build an initramfs with the SpeedTouch firmware into 
> the kernel, how much else will I need to include to get this to work? 
> Surely to load the firmware I'll also need to include /sbin/udevsend, 
> /etc/udev/rules.d/10-udev.rules, /sbin/firmware_helper...and what 
> else? Won't these things need a whole load of other things? This is 
> looking very complicated. 

The general case is indeed very complicated, SUSE's script for creating 
initramfs is more than 64K long. But since you are interested only in 
firmware loading, the following stupid hack may work for you. The hack 
is to put a firmware hotplug handler into initramfs, but still rely upon 
the (obsolete) builtin kernel mechanism for creating and mounting the 
root device.

I do use an initramfs because my root filesystem is on LVM2, and also 
because of suspend2 with swap on LVM2. But it doesn't load any firmware 
because my devices don't need that.

Details for firmware-loading initramfs (untested, since none of my 
devices generate firmware hotplug events):

1) Compile klibc, for small-sized "cat", "mount", "sleep", "sh" and 
"umount" programs, as follows:

Download and unpack 
http://www.kernel.org/pub/linux/libs/klibc/Stable/klibc-1.1.1.tar.bz2

Replace "flag = 0" with "flag = MNT_DETACH" in utils/umount.c, line 15, 
so that umount is lazy.

ln -s /lib/modules/`uname -r`/build linux
make

and optionally "make install"

Find those small statically linked programs in ash/sh, 
utils/static/{cat,mount,sleep,umount}.

Alternatively, use glibc-based utils from your existing system, but then 
you should copy the required libraries into /lib at step (3) below.

2) Install cpio

3) Make a directory and populate it with the following files:

dev/{console,null} (you should know how to mknod them)
bin/{sh,cat,mount,sleep,umount} (from klibc)
sys (empty directory)
sbin/hotplug (see the contents below)
lib/firmware (copy your firmware files there)

The /sbin/hotplug script should contain the following:

#!/bin/sh
[ "$1" != "firmware" ] || [ "$ACTION" != "add" ] || [ ! -f 
"/lib/firmware/$FIRMWARE" ] || exit 0
mount -t sysfs sysfs /sys
# FIXME: still needed?
if [ ! -e /sys/$DEVPATH/loading ]; then
    sleep 1
fi
echo 1 > /sys/$DEVPATH/loading
cat "/lib/firmware/$FIRMWARE" >/sys/$DEVPATH/data
echo 0 > /sys/$DEVPATH/loading
umount /sys  # racy, see below

Then cd to this directory and create the initramfs:

find . | cpio -o -H newc | gzip -9 > /boot/initramfs_data.cpio.gz

4) modify your boot loader configuration in order to load 
initramfs_data.cpio.gz as an initrd.

5) Reboot. Please report if firmware loading from this initramfs 
actually worked for you.

------------------------------
Now about my initramfs.

As you have noticed, the simple initramfs above doesn't include the 
/init file and thus relies on the obsolete in-kernel mechanism for 
mounting the root fs. This is racy because mounting/unmounting of /sys 
in the hotplug handler and in the kernel (or in two instances of hotplug 
handler) can clash. Also this doesnn't work in my case because there's 
some non-trivial work required in order to activate LVM2 and resume from 
swsusp2 when swap is on LVM2.

Thus, I have to use the /init file. It is just a shell script. If this 
script is present in initramfs, it is executed instead of mounting the 
root fs. It's then the responsibility of the script to parse the kernel 
command line and mount the filesystem.

My initramfs is glibc-based, doesn't use udev, and contains all device 
nodes needed for the "vgchange -ay" command to run. The contents of the 
/init script:

#!/bin/sh

mount -n -t proc proc /proc
mount -n -t sysfs sysfs /sys

# Needed in order to activate LVM2
# Relies upon /dev/mapper/control and /dev/hda being present
vgchange -ay

init=/sbin/init
ro="ro"
read CMDLINE </proc/cmdline

for ARG in $CMDLINE
do
        case "$ARG" in
                init=*)
                        init=${ARG#init=}
                        ;;
                root=*)
                        root=${ARG#root=}
                        ;;
                ro)
                        ro="ro"
                        ;;
                rw)
                        ro="rw"
                        ;;
        esac
done

echo >/proc/suspend2/do_resume

# We get here when we are not resuming.
mount -n -o "$ro" "$root" /root

umount -n /sys
umount -n /proc

# run-init is a program from klibc, but it compiles fine against glibc too.
exec run-init /root "$init" "$@" </root/dev/console >/root/dev/console

Isn't that simple enough? :)

Also this /init file helps avoiding the /sys mounting race: just don't 
unmount it in the hotplug handler. This /init file will do that for you 
at the very end.

-- 
Alexander E. Patrakov



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