Re: initramfs: udev, hotplug, klibc and modprobe

[Kay Sievers <kay.sievers@vrfy.org>]

On Sun, 2005-01-09 at 23:25 +0100, Juerg Billeter wrote:
> As I couldn't find a documented way how to use initramfs together with
> udev, hotplug, klibc and modprobe, I've done some tests myself. I wanted
> to enable booting a fully modular kernel without initrd and custom
> hardware detection scripts on any linux-supported hardware (ide, scsi,
> usb whatever).
> 
> Meanwhile it's gotten to work very well but I had to write some patches,
> scripts, little programs myself and so I thought to write down how I
> build my initramfs and I'd like to get comments from people actively
> working on udev and related technology whether my implementation makes
> sense or I've completely misunderstood something.
> 
> Following my rough initramfs kernel build instructions, my files are
> marked with a footnote
> 
>       * Build a fully modular kernel without initramfs (2.6.10)
>       * Build klibc (0.196) and copy ash and the static utils to
>         initramfs
>               * [1] Patch to add a stripped down, klibc-compatible
>                 version of module-init-tools' modprobe to the build
>       * Build udev (050) with klibc and copy it to initramfs
>               * [2] Patch to shorten event timeout from 10s to 3s and
>                 set the expected hotplug seqnum start to 5 to avoid the
>                 event timeout as I've never seen a hotplug event with a
>                 seqnum < 5, am I missing some?

The next version of udevd will have a timeout of only 2 seconds during a
startup phase. This may not be needed then.

>               * [3] Patch to add udevinitd and udevinitsend. These are
>                 modified versions of udevd and udevsend acting as a
>                 "caching daemon". They save events received during early
>                 userspace and resend them to late userspace udevd when
>                 ready. This enables late userspace to process all events
>                 (for example to load modules not included in initramfs)
>                 without using coldplugging and thelike. (udevinitsend
>                 gets called via hotplug.d)

Nice idea. In a recent discussion, the question came up about a possible
combination of udevstart and coldplugging. It may be possible to
synthesize all the events from the information in sysfs? What do you
think about that in relation to your udevd "event queue".

Thanks,
Kay



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