Re: [Xen-devel] [PATCH v4 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.06.16 at 13:18, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> On 6/16/2016 6:02 PM, Jan Beulich wrote:
>>>>>>> +struct xen_hvm_map_mem_type_to_ioreq_server {
>>>>>>> +    domid_t domid;      /* IN - domain to be serviced */
>>>>>>> +    ioservid_t id;      /* IN - ioreq server id */
>>>>>>> +    uint16_t type;      /* IN - memory type */
>>>>>>> +    uint16_t pad;
>>>>>> This field does not appear to get checked in the handler.
>>>>> I am now wondering, how about we remove this pad field and define type
>>>>> as uint32_t?
>>>> As above - I think the current layout is fine. But I'm also not heavily
>>>> opposed to using uint32_t here. It's not a stable interface anyway
>>>> (and I already have a series mostly ready to split off all control
>>>> operations from the HVMOP_* ones, into a new HVMCTL_* set,
>>>> which will make all of them interface-versioned).
>>> I'd like to keep this interface. BTW, you mentioned "this field does not
>>> appear to
>>> get checked in the handler", do you mean we need to check the pad in the
>>> handler?
>> Yes.
>>
>>> And why?
>> In order to be able to later assign meaning to it without breaking
>> existing users.
> 
> So the handler need to assure the pad is 0, right?

Correct.

Jan


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