Re: [Xen-devel] [PATCH RFC 04/13] x86/mm: carve out create_grant_pv_mapping

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 29/03/17 11:45, Jan Beulich wrote:
>>>> On 29.03.17 at 12:27, <andrew.cooper3@xxxxxxxxxx> wrote:
>> One idea I had while starting the hypercall work was to introduce a
>> "struct guest_type_ops" to contain some function pointers for options we
>> perform on all guests, irrespective of type.  My first candidate for
>> splitting this way was the hypercall page writing.
>>
>> This splitting here is subtly different.  Its more "struct
>> paging_type_op", but still common operations we would need to perform
>> for guests.
>>
>> I was thinking that ops structures like this would be cleaner to isolate
>> than needing an explicit dispatch functions such as
>> create_grant_host_mapping() below.
>>
>> Thoughts, (seeing as this is the first time I have floated this idea on
>> xen-devel) ?
> I think that's reasonable as long as we don't go too far with this
> (indirect calls after all generally having a higher overhead than
> mis-predicted branches).

Without any #ifdefary in a source tree, that is fine.  It is harder
however if you want to conditionally compile things out.

A alternative option would be to have a static inline in a header file
which contains the appropriate #ifdefary internally.

~Andrew

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