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

To: Anthony Liguori <aliguori@xxxxxxxxxx>
Subject: Re: [Xen-tools] [PATCH] An example console driver using the store
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Tue, 9 Aug 2005 08:24:16 +0100
Cc: Xen Tools <xen-tools@xxxxxxxxxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>, hollis <hollisb@xxxxxxxxxx>, Jimi Xenidis <jimix@xxxxxxxxxx>, Robert Read <robert@xxxxxxxxxxxxx>
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On 9 Aug 2005, at 03:01, Anthony Liguori wrote:

Argh! I wrote this exactly to show that shoving more crap in the
start_info struct was a bad idea!

I figured you'd say that. The console seems like a special case though. I'm sort of on the fence about it. What does everyone else think?

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. If we start getting reports of silently hanging/failing domUs in the field, it's not really good enough to have to ask people to turn on skanky debug hacks for something that ought to be so simple.

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.

 -- Keir

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