Re: [Xen-devel] [PATCH V2] common/mem_access: merged mem_access setting interfaces

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.03.17 at 17:16, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 03/20/2017 06:14 PM, Razvan Cojocaru wrote:
>> On 03/20/2017 06:07 PM, Jan Beulich wrote:
>>>>>> On 20.03.17 at 10:50, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>>> --- a/xen/include/public/memory.h
>>>> +++ b/xen/include/public/memory.h
>>>> @@ -444,6 +444,8 @@ struct xen_mem_access_op {
>>>>      /* xenmem_access_t */
>>>>      uint8_t access;
>>>>      domid_t domid;
>>>> +    uint16_t view_id;
>>>> +    uint16_t pad[3];
>>>
>>> Irrespective of Andrew's valid general objection, the change above
>>> wouldn't be valid either: How would you guarantee compatibility
>>> with old callers? Other than in e.g. domctl/sysctl there's no
>>> interface version here which can be bumped, so simply adding
>>> fields to a structure and re-using an existing sub-op won't do.
>> 
>> I wouldn't - I thought simply bumping the DOMCTL version macro would be
>> enough, but obviously I could just add other DOMCTLs and return an error
>> for the old ones.

I miss the connection to domctl here - this is a mem-op, isn't it?

>> In any case, back when I've added xc_set_mem_access_multi() I've also
>> modified struct xen_mem_access_op in the same manner:
>> 
>> 
> http://xenbits.xenproject.org/gitweb/?p=xen.git;a=commitdiff;h=1ef5056bd6274e 
> cbe065387b6cf45657d6d700cd
> 
> Oh, nevermind, I think you're referring to the fact that I had back then
> added members to the end of the structure, and so the old layout had
> remained compatible. Point taken.

Not just that - there you've also introduced a new sub-op.

Jan


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