On 6/16/11 3:06 PM, Gleb Kurtsou wrote:
On (16/06/2011 13:32), Russell Cattelan wrote:
I have been contacted about possibly implementing a fast reboot
mechanism for FreeBSD similar to kexec on Linux.
I have just started looking into how this accomplished so I figured
a note to freebsd hackers would also be a good place to ask
for comments.
Has anybody looked at doing something like kexec?
I was working on similar project some time ago. First of all you have to
leave hardware in known good state for a new kernel. Reseting devices
can be generally accomplished by unloading corresponding kernel modules
(even if they are compiled in kernel). The biggest problem for me was
timers and programmable interrupt controller. I didn't make it work
properly, but my goals where much wider than replacing with another
FreeBSD kernel. Aim was to restore initial BIOS state as much as
possible.
What were your goals beyond booting a new kernel? I think getting back
to a known BIOS state is kinda required to get a kernel through the boot
process. From what I can tell the main goal of kexec is to avoid the process
of re-initializing the hardware via BIOS.
Is it the right thing to do for FreeBSD. I'm concerned that the way
FreeBSD handles early kernel modules (loaded via the boot loader)
vs linux which does everything via initrd is going to be a problem.
I find loader code easy work with. You could write dummy filesystem
implementation for libstand. So that customized loader will load both
kernel and modules yet while running FreeBSD. Your "reboot" procedure
wouldn't even use any BIOS io interrupts. Linux boot is a real mess
imho.
So it is possible to get back to the loader once the kernel is booted?
So the running kernel could load the new kernel / modules and then jump
back to the loader to start the boot process.
Thanks for any help on this.
-Russell Cattelan
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