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

On 23/03/16 19:03, Juergen Gross wrote:
> 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?

I am not convinced that the use case is sufficiently compelling to
warrant adding to the Linux kernel ABI.

New ABIs need to solve problems not just present possibly useful


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