Adventures with kexec

You may know, my laptop is in a rather horrible state – it has no harddisk, and the BIOS only boots off harddisks and CD-ROMs.  It seems difficult/impossible to find a replacement harddisk due to the strange size and connector.  So, I use a PCMCIA (PCCARD) CFCard adapter for a root filesystem and knocked together a boot CD for the kernel and initrd.  In the initrd I wrote a custom linuxrc script to bootstrap PCMCIA, mount the root fs, and hand over to init.

The obvious problem with this solution is, every time I want to update the kernel or change a compiled in feature, I have to reburn the boot CD, which gets boring very quickly.  I heard about something called “kexec” a while back, and suddenly realized this morning (While hung over after a party and having been woken up at 9AM to help with heavy lifting…) that kexec could solve a number of these problems.

What I do is, the boot CD loads up PCMCIA stuff, mounts the PCMCIA drive, then finds a new kernel and initrd and uses kexec to then boot that newer kernel and initrd.  Therefore, all I need to do to update my kernel is copy the new kernel to /superduperbootcd on the root filesystem – dead easy.

There are a couple of drawbacks, mainly that going through two partial boot cycles takes a while, and any bugs in the kernel which appear during the first boot will need me to burn the boot CD again.  But it’s still quite a neat solution, very cool, and a reason I love linux.

Speaking of bugs which appear during booting, occasionally my kernel segfaults on boot, before it even executes INIT – the backtrace mentions sony_laptop_init, or something similar.  Has anybody heard of this bug, or know of a way to fix it?  It seems more common when my power cable is not connected, but that could just be me.

(Waiting for my pickups from rapid….)

Cheers