Date: Thu, 16 Jun 2011 22:35:53 -0500 From: Russell Cattelan <cattelan@thebarn.com> To: Gleb Kurtsou <gleb.kurtsou@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: kexec or similar for FreeBSD Message-ID: <4DFACB99.1030707@thebarn.com> In-Reply-To: <20110616200616.GA67011@tops> References: <4DFA4C47.8060503@digitalelves.com> <20110616200616.GA67011@tops>
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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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