Re: [Xen-devel] [PATCH v3 1/3] docs: add a document describing the 'channels' mechanism

[Dave Scott <Dave.Scott@xxxxxxxxxx>]

On 24 Jun 2014, at 11:43, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> wrote:

> Dave Scott writes ("Re: [PATCH v3 1/3] docs: add a document describing the 
> 'channels' mechanism"):
>> On 23 Jun 2014, at 15:53, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> wrote:
>>> I forgot to ask: what will a guest do that doesn't understand these
>>> special-purpose "console"s ?
>> 
>> In a Linux VM they’ll just appear as /dev/hvcX devices. I assume something 
>> similar in a *BSD.
> 
> ... and then what would happen with them ?  Nothing ?  If so, fine.
> 
> I'm just worried that something might automatically mess with them.
> E.g. I have found a horrid thing called "modem-manager" on some
> desktop Linuces which opens (all?) serial devices and tries blathering
> AT commands at them…

The uses for these channels all involve talking to some specific software 
inside the guest, for example an “early configuration” service or a guest 
agent. It only makes sense to connect a channel to a guest if your guest has 
been configured to expect it. You would install your VM as normal, install your 
special software, shutdown, add the channels, possibly clone/publish your guest 
as a template and then restart.

You’re right that an unconfigured or misconfigured guest could do anything in 
theory. Your AT command scenario sounds quite realistic and would make a good 
example in the docs of why in-guest configuration is necessary.

I think I should elaborate more on the use-cases in the docs to make all this 
clearer.

Cheers,
Dave
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