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

From: George Dunlap <George.Dunlap@eu.citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Juergen Gross <jgross@suse.com>, Wei Liu <wei.liu2@citrix.com>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
	David Vrabel <david.vrabel@citrix.com>,
	Jan Beulich <JBeulich@suse.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH] tools: fix xen-detect to correctly identify domU type
Date: Thu, 24 Mar 2016 11:38:39 +0000	[thread overview]
Message-ID: <CAFLBxZbria7Qm=LV0N1US+8ZjWhF0q3G1fS2NdTwdd2pAjcTLw@mail.gmail.com> (raw)
In-Reply-To: <56F3CE21.8000004@citrix.com>

On Thu, Mar 24, 2016 at 11:23 AM, Andrew Cooper
<andrew.cooper3@citrix.com> wrote:
> 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.

FWIW this sounds reasonable to me.

 -George

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