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

From: Andrew Cooper <andrew.cooper3@citrix.com>
To: David Vrabel <david.vrabel@citrix.com>,
	Juergen Gross <jgross@suse.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: Wed, 23 Mar 2016 11:25:18 +0000	[thread overview]
Message-ID: <56F27D1E.2040700@citrix.com> (raw)
In-Reply-To: <56F27B78.9000109@citrix.com>

On 23/03/16 11:18, David Vrabel wrote:
> On 23/03/16 11:12, Andrew Cooper wrote:
>> On 23/03/16 10:59, David Vrabel wrote:
>>> On 23/03/16 10:55, Andrew Cooper wrote:
>>>> On 23/03/16 10:52, Juergen Gross wrote:
>>>>> On 23/03/16 11:32, David Vrabel wrote:
>>>>>> On 23/03/16 10:25, Jan Beulich wrote:
>>>>>>>>>> On 23.03.16 at 11:14, <JGross@suse.com> wrote:
>>>>>>>> 7. Report type according to features found (this is a little bit
>>>>>>>>    ugly: we have to rely on the current hypervisor implementation
>>>>>>>>    regarding the bits set for the different guest types).
>>>>>>> Well, in some of the cases feature flags only make sense for one
>>>>>>> kind of guest, so if such a flag is set it could be used as positive
>>>>>>> indication (while it being clear may then still mean nothing).
>>>>>>>
>>>>>>>> Would it make sense to add another file to /sys/hypervisor/properties?
>>>>>>>> Something like guest_type, containing "pv", "hvm" or "pvh"? If existing
>>>>>>>> this could be used to report the guest type.
>>>>>>> That would seem a good idea to me. What do others, namely
>>>>>>> Linux maintainers, think?
>>>>>> What's the use case for user space knowing if it's in a PV or HVM domain?
>>>>> The first thing coming to my mind would be diagnostic tools.
>>>> Having the admin able to tell for informational purposes is useful. 
> This is useful because...?

Independently verifying that the guest is as expected?

>
>>>> They can find out by looking at the top of `dmesg`, but a hypervisor
>>>> sysfs node is cleaner than requiring the admin to know every printk()
>>>> variant that Xen puts out.
>>>>
>>>> That is it however.  It specifically shouldn't be used for any other
>>>> decisions, as it isn't relevant.
>>> I think it should be the toolstack that presents this information.
>>>
>>> I don't think we should add a new kernel ABI for this.
>> A toolstack is not present in a domU.
> So?  The guest admin doesn't need to be in the guest itself to get this
> information -- it's right there is the xl configuration for the guest.

guest admin != host admin, and had better not have access to dom0.

~Andrew

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