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

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

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.
> 
> 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=1ef5056bd6274ecbe065387b6cf45657d6d700cd

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.


Thanks,
Razvan

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