Messages in this thread | | | Subject | Re: Announce: dumpfs v0.01 - common RAS output API | From | (Eric W. Biederman) | Date | 27 Jul 2004 19:53:01 -0600 |
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Andrew Morton <akpm@osdl.org> writes:
> Keith Owens <kaos@sgi.com> wrote: > > > > * How do we get a clean API to do polling mode I/O to disk? > > We hope to not have to. The current plan is to use kexec: at boot time, do > a kexec preload of a small (16MB) kernel image. When the main kernel > crashes or panics, jump to the kexec kernel. The kexec kernel will hold a > new device driver for /dev/hmem through which applications running under > the kexec'ed kernel can access the crashed kernel's memory.
Hmm. I think this will require one of the kernels to run at a non-default address in physical memory.
> Write the contents of /dev/hmem to stable storage using whatever device > drivers are in the kexeced kernel, then reboot into a real kernel > again.
And at this point I don't quite see why you would need /dev/hmem, as opposed to just using /dev/mem.
Or will the crashing kernel save and compress the core dump to somewhere in ram and the dump kernel read it out from there?
> That's all pretty simple to do, and the quality of the platform's crash > dump feature will depend only upon the quality of the platform's kexec > support.
Which will largely depend on the quality of it's device drivers...
> People have bits and pieces of this already - I'd hope to see candidate > patches within a few weeks. The main participants are rddunlap, suparna > and mbligh.
I'm sorry I missed you then. Unfortunately this is my busiest season at work so I wasn't able to make it to OLS this year :(
Does anyone have a proof of concept implementation? I have been able to find a little bit of time for this kind of thing lately and have just done the x86-64 port. (You can all give me a hard time about taking a year to get back to it :) I am in the process of breaking everything up into their individual change patches and doing a code review so I feel comfortable with sending the code to Andrew. So this would be a very good time for me to look at any code for reporting a crash dump with a kernel started with kexec.
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