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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: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Date: Tue, 09 Aug 2005 11:50:04 +1000
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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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!

> 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.

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,

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

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