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

To: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Subject: Re: [Xen-tools] [PATCH] An example console driver using the store
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Mon, 08 Aug 2005 21:01:40 -0500
Cc: Xen Tools <xen-tools@xxxxxxxxxxxxxxxxxxx>, hollis <hollisb@xxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>, Jimi Xenidis <jimix@xxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>, Robert Read <robert@xxxxxxxxxxxxx>
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Rusty Russell wrote:

On Mon, 2005-08-08 at 12:37 -0500, Anthony Liguori wrote:
Hi Rusty,

One thing we might want to consider doing is having the domain builder allocate a page/event channel for the first console.

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?

This gives us access to the console in a guest at start of day (and would work even if the store is not running). I think this later reason is particuarily important since it's hard to debug the XenBus code in a guest without a console.

There's still the hcall which prints out stuff, for emergency debugging.
If the store daemon isn't up you should not be starting domUs: you'll
have no devices and no console.
The emergency console is meant for dom0.


Anthony Liguori

And even if the writes fail you can get the values out of the trace
output of xenstored if you're in debugging mode.

Also, it allows the PPC guys to hack up the hypervisor to support the PAPR console stuff since they can get to the ring buffer by examining the shared_info_frame. It's not a long term solution but it's useful.

They can also make their own ring buffer and publish it in the same way,


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