Re: [Xen-devel] [PATCH 0001/001] xen: multi page ring support for block devices

["Justin T. Gibbs" <gibbs@xxxxxxxxxxx>]

On Mar 6, 2012, at 1:34 AM, Jan Beulich wrote:

>>>> On 05.03.12 at 22:49, Santosh Jodh <Santosh.Jodh@xxxxxxxxxx> wrote:

…

>> +       }
>> +
>>        /* Create shared ring, alloc event channel. */
>>        err = setup_blkring(dev, info);
>>        if (err)
>> @@ -889,12 +916,35 @@ again:
>>                goto destroy_blkring;
>>        }
>> 
>> -       err = xenbus_printf(xbt, dev->nodename,
>> -                           "ring-ref", "%u", info->ring_ref);
>> -       if (err) {
>> -               message = "writing ring-ref";
>> -               goto abort_transaction;
>> +       if (legacy_backend) {
> 
> Why not use the simpler interface always when info->ring_order == 0?

Because, as I just found out today via a FreeBSD bug report, that's
not how XenServer works.  If the front-end publishes "ring-page-order",
the backend assumes the "ring-refNN" XenStore nodes are in effect,
even if the order is 0.

I'm working on a documentation update for blkif.h now.

<sigh>

--
Justin
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