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Re: [Xen-tools] [PATCH] An example console driver using the store

On Tue, 2005-08-09 at 08:24 +0100, Keir Fraser wrote:
> It's going in start_info I'm afraid. If things go bad early in boot or 
> early after restore/resume, I want debug output from the kernel, 
> *without* xprintk hacks and debug builds of Xen. There's a 
> prettiness/practicality tradeoff here: most of us in Cambridge err 
> towards the latter.
> Kernel console must be highly available. Making it dependent on 
> xenstore/xenbus in domain0 and in the kernel itself doesn't achieve 
> that imo.

I'd far prefer to have a __HYPERVISOR_panic_message hcall which copied
up to 80 chars into a per-domain buffer that can be queried from dom0.
The console driver would presumably use this (once) on catastrophic
failure, and could be useful for other similar things (panic?).

I bow to your greater wisdom, however, even when you are wrong 8)

> Perhaps we should at least be taking Rusty's store layout code though. 
> We certainly still want to include details of emergency console in teh 
> xenstore, to be picked up by xenbus when it starts, and any other 
> consoles (e.g., user-space tty1 and so on) will all get set up via 
> xenbus. So we do need some xenbus- and xenstore-interfacing code.

If you want multiple consoles you'll need a different layout anyway.  On
something that isn't a physical machine that seems a strange thing to do

A bad analogy is like a leaky screwdriver -- Richard Braakman

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