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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.03.17 at 17:48, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 03/20/2017 06:40 PM, Jan Beulich wrote:
>>>>> On 20.03.17 at 17:16, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> On 03/20/2017 06:14 PM, Razvan Cojocaru wrote:
>>>> 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.
> 
> Yes, but by modifying the structure for use with
> XENMEM_access_op_set_access_multi, it's now also changed for, e.g.,
> XENMEM_access_op_set_access - since it's common to them. Other than the
> place where the new data has been added, I believe that the same
> critique would apply to the old patch, unless I'm misunderstanding
> something.

Indeed, strictly speaking that change wasn't really okay either,
as someone passing the smaller structure near the end of a page
might get -EFAULT back. So we're trying to do better this time ...

Jan


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