Re: [PATCH] tools: fix xen-detect to correctly identify domU type

From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Juergen Gross <jgross@suse.com>,
	David Vrabel <david.vrabel@citrix.com>,
	Jan Beulich <JBeulich@suse.com>
Cc: ian.jackson@eu.citrix.com,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	xen-devel@lists.xen.org, wei.liu2@citrix.com,
	stefano.stabellini@eu.citrix.com
Subject: Re: [PATCH] tools: fix xen-detect to correctly identify domU type
Date: Thu, 24 Mar 2016 11:23:13 +0000	[thread overview]
Message-ID: <56F3CE21.8000004@citrix.com> (raw)
In-Reply-To: <56F3C85F.5030903@suse.com>

On 24/03/16 10:58, Juergen Gross wrote:
> I've searched a little bit in git history in order to understand why
> xen-detect has been invented and/or has all the options which clearly
> are meant to be used in scripts.
>
> The last large modification was done in 2009 and I think Konrad is to
> blame here. ;-)
>
> It was meant to be used in early boot sequence to autoload the needed
> modules (frontends/backends) in case of running on top of Xen. I believe
> this usage isn't needed any longer as the dom0 case is handled
> differently and the needed frontends are loaded automatically on demand.
>
> So this means we can drop all the options of xen-detect, as they serve
> no purpose today.
>
> Next question is whether the remaining functionality warrants keeping
> xen-detect, and how the information it is presenting can be obtained.
>
> If we want to keep it, I can think of following solutions:
> - new kernel ABI (as suggested, David doesn't like it)
> - follow the route it is taking today, information is unreliable
> - parsing of the boot messages (e.g. via an init script into a file)
>   and printing that information (would work, but is a little bit hacky)
>
> Thoughts?

I don't recommend keeping xen-detect.  It is unreliable, and we will
always be playing catchup.

Parsing? that's not a little hacky...  The ABI is definitely a better
solution.

As for the ABI,

[root@fusebot ~]# find /sys/hypervisor/
/sys/hypervisor/
/sys/hypervisor/type
/sys/hypervisor/uuid
/sys/hypervisor/compilation
/sys/hypervisor/compilation/compiled_by
/sys/hypervisor/compilation/compile_date
/sys/hypervisor/compilation/compiler
/sys/hypervisor/properties
/sys/hypervisor/properties/pagesize
/sys/hypervisor/properties/changeset
/sys/hypervisor/properties/virtual_start
/sys/hypervisor/properties/features
/sys/hypervisor/properties/capabilities
/sys/hypervisor/version
/sys/hypervisor/version/extra
/sys/hypervisor/version/major
/sys/hypervisor/version/minor

A /sys/hypervisor/guest_type property would fit nicely alongside uuid,
and is applicable to all hypervisors, not just Xen.

~Andrew

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