Re: [Xen-devel] [PATCH 4 of 5] blkif.h: Document the RedHat and Citrix blkif multi-page ring extensions

[Justin Gibbs <justing@xxxxxxxxxxxxxxxx>]

On Feb 3, 2012, at 6:33 AM, Jan Beulich wrote:

>>>> On 03.02.12 at 06:24, "Justin T. Gibbs" <justing@xxxxxxxxxxxxxxxx> wrote:
>> @@ -187,6 +216,25 @@
>>  *      The machine ABI rules governing the format of all ring request and
>>  *      response structures.
>>  *
>> + * ring-page-order
>> + *      Values:         <uint32_t>
>> + *      Default Value:  0
>> + *      Maximum Value:  MAX(ffs(max-ring-pages) - 1, max-ring-page-order)
> 
> Why not just max-ring-page-order. After all, the value is meaningless
> for a backend that only exposes max-ring-pages.
> 
>> + *      Notes:          1, 3
>> + *
>> + *      The size of the frontend allocated request ring buffer in units
>> + *      of lb(machine pages). (e.g. 0 == 1 page, 1 = 2 pages, 2 == 4 pages,
>> + *      etc.).
>> + *
>> + * ring-pages
>> + *      Values:         <uint32_t>
>> + *      Default Value:  1
>> + *      Maximum Value:  MAX(max-ring-pages,(0x1 << max-ring-page-order))
> 
> Similarly here - just max-ring-pages should do.

This patch documents existing extensions.  For a new driver to properly 
negotiate a
multi-page ring with a Dom0 on EC2 (ring-pages) or a Citrix Dom0/guest 
(ring-page-order),
you must use the XenBus node names as I've defined them here.

--
Justin
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