Re: [Xen-devel] [PATCH v2 0/2] Remove PAGE_SIZE from public headers

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 20/10/16 20:09, Stefano Stabellini wrote:
> On Thu, 20 Oct 2016, Juergen Gross wrote:
>> On 19/10/16 21:21, stefano@xxxxxxxxxxx wrote:
>>> Reference to PAGE_SIZE slipped in to two public header files. QEMU build on
>>> ARM64 is broken by this. PAGE_SIZE should not be used because it could
>>> be undefined or it could be defined differently on different operating
>>> systems.
>>>
>>> Stefano Stabellini (2):
>>>       usbif.h: replace PAGE_SIZE with USBIF_RING_SIZE
>>>       vscsiif.h: replace PAGE_SIZE with VSCSIIF_PAGE_SIZE
>>>
>>>  xen/include/public/io/usbif.h   | 5 +++--
>>>  xen/include/public/io/vscsiif.h | 3 ++-
>>>  2 files changed, 5 insertions(+), 3 deletions(-)
>>>
>> In principle I'm okay with these changes. But wouldn't it be
>> better to add
>>
>> #define XEN_RING_PAGE_SIZE 4096
>>
>> to xen/include/public/io/ring.h instead of having each interface
>> file its own definition?
> I would prefer to avoid having to spell out the page size for all the io
> interfaces, because the same interfaces should work fine with other page
> granularities, if the grant table hypercalls supported them.
>
> However in reality frontend and backend would have to agree on the page
> granularity to use beforehand. Some sort of consensus protocol is
> required. When that protocol is introduced, we could get rid of
> #define XEN_RING_PAGE_SIZE 4096.
>
> What do people think about this?

Not all current rings are 4k in size, and not all future rings should be
implicitly restricted to 4k.

-1 to this introducing XEN_RING_PAGE_SIZE.  It will be more confusing
than helpful.

~Andrew

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