Re: [PATCH v13] This is the ABI for the two halves of a para-virtualized sound driver to communicate with each to other.

[Oleksandr Andrushchenko <andr2000@gmail.com>]

On 11/28/2016 05:00 PM, Julien Grall wrote:
> Hi Oleksandr,
>
> On 28/11/16 14:56, Oleksandr Andrushchenko wrote:
>> On 11/28/2016 04:24 PM, Julien Grall wrote:
>>> Hi Oleksandr,
>>>
>>> On 28/11/16 14:12, Oleksandr Andrushchenko wrote:
>>>>
>>>> On 11/28/2016 03:27 PM, Jan Beulich wrote:
>>>>>> + *
>>>>>> + * gref_dir_next_page - grant_ref_t, reference to the next page
>>>>>> describing
>>>>>> + *   page directory. Must be 0 if no more pages in the list.
>>>
>>> If I am not mistaken 0 is a valid grant.
>>>
>> Then I will remove this sentence, anyways BE knows how many grefs there
>> are for the buffer size given
BTW, xen-blkfrint.c:
#define GRANT_INVALID_REF    0
this is from where I got "Must be 0 if no more pages in the list."
>>>>>> + * gref[i] - grant_ref_t, reference to a shared page of the buffer
>>>>>> + *   allocated at XENSND_OP_OPEN
>>>>>> + *
>>>>>> + * Number of grant_ref_t entries in the whole page directory is not
>>>>>> + * passed, but instead can be calculated as:
>>>>>> + *   num_grefs_total = DIV_ROUND_UP(XENSND_OP_OPEN.buffer_sz,
>>>>>> PAGE_SIZE);
>>>>> The header should be self contained, and there's no DIV_ROUND_UP()
>>>>> anywhere under public/io/ for a reader to refer to. Please express 
>>>>> this
>>>>> using mathematical terms plus, if needed, standard C library ones.
>>>> done, will put:
>>>> num_grefs_total = (XENSND_OP_OPEN.buffer_sz + PAGE_SIZE - 1) / 
>>>> PAGE_SIZE
>>>
>>> Can we avoid to use PAGE_SIZE in the header? Xen, the front-end and
>>> the back-end may have different page size.
>>>
>> then, I believe, the protocol should implement something like blkif 
>> does?
>> Multi-page buffer which depends on front and back page sizes?
>> (blkif: max-ring-page-order/ring-ref%u/ring-page-order)
>> Is this what you mean?
>
> It is not what I meant. I asked to define PAGE_SIZE. Is it the the 
> PAGE_SIZE of Xen? PAGE_SIZE of the backend? PAGE_SIZE of the frontend?
>
> Currently PV driver PAGE_SIZE is based on the size of a grant page.
As per my understanding, I can put XEN_PAGE_SIZE here, because 
xen/page.h says:
" * We assume that PAGE_SIZE is a multiple of XEN_PAGE_SIZE
  * XXX: Add a BUILD_BUG_ON?
"
meaning that PAGE_SIZE on either side cannot be less than XEN_PAGE_SIZE
Will XEN_PAGE_SIZE fit then?
> Regards,
>


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