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

[Juergen Gross <jgross@xxxxxxxx>]

On 23/03/16 12:25, Andrew Cooper wrote:
> 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@xxxxxxxx> 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.

David, do you agree on adding another /sys file? Or do you still think
this is no good idea? In case you don't like it, do you have a better
alternative?


Juergen


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