Re: [Xen-devel] Little help with blk ring

[Daniel Castro <evil.dani@xxxxxxxxx>]

I am writing the PV Driver front end in Seabios.

Could you explain your method in a little more detail please?

Thanks,

Daniel

On Mon, May 7, 2012 at 5:53 PM, James Harper
<james.harper@xxxxxxxxxxxxxxxx> wrote:
>> >
>> > >>> On 07.05.12 at 08:23, Daniel Castro <evil.dani@xxxxxxxxx> wrote:
>> > > Hello List,
>> > >
>> > > I have a small problem with the ring when transferring blocks the id
>> > > on the response is different from the request.
>> > > This is the boot up read, count 0.
>> > > The guest requests block 0, it has to be located at 7c00.
>> > >
>> > > I go ahead and create a REQUEST with this data:
>> > > ring_req = RING_GET_REQUEST(priv,priv->req_prod_pvt);
>> > > ring_req->id = 9;
>> > > ring_req->nr_segments=1;
>> > > ring_req->operation = BLKIF_OP_READ; ring_req->sector_number =
>> > > (int)op->lba; //sector to be read ring_req->seg[0].gref =
>> > > (bi->buffer_gref); //this should be get_free_gref();
>> > > ring_req->seg[0].first_sect = 0;//op->lba;
>> > > ring_req->seg[0].last_sect = 7;//op->lba + op->count;
>> > >
>> > > RING_PUSH_REQUESTS_AND_CHECK_NOTIFY((priv),notify);  //return
>> > notify=0
>> > > if(notify){
>> > >           dprintf(1,"Start notify procedure\n");
>> > >           evtchn_send_t send;
>> > >           send.port = (bi->port);
>> > >           dprintf(1,"In notify before hypercall port is %d\n",send.port);
>> > >           //hypercall_event_channel_op(EVTCHNOP_send, &send);
>> > >           dprintf(1,"HYPERCALL read operation notify res %d\n",
>> > > hypercall_event_channel_op(EVTCHNOP_send,&send));
>> > > }
>> > > ring_res = RING_GET_RESPONSE((priv),(temp->rsp_prod));
>> > > Then I get:
>> > > FAIL RING RESPONSE 0x0009a040 id:256 status:9 operation 0 this is
>> > > the line:
>> > > dprintf(1,"FAIL RING RESPONSE %p id:%d status:%d operation %d\n",
>> > > ring_res,ring_res->id,ring_res->status,ring_res->operation);
>> > >
>> > >
>> > > The id should be the same on both the request and response, there
>> > > are bi ither requests on the fly.
>> > >
>> > > Any clue?=
>> >
>> > With status happening to be 9 when id should be, is this perhaps a
>> > broken response structure definition?
>> >
>>
>> That would be my guess too. The structure aligns differently under 64 and 32
>> bits so I'd guess the OP is talking between the two.
>>
>
> Further to this, Dom0 sets the "protocol" entry in the frontend xenstore 
> (/local/domain/<domu id>/device/vbd/<vbd id>/protocol) to tell it what 
> alignment it is using. I wrote GPLPV before this setting existed so I solved 
> the problem by sending 2 invalid requests down the ring and checking the 
> response. If the fields have shifted around I assume that dom0 is not the 
> same bit width as the domu and switch structure definitions on the fly.
>
> Are you writing a new frontend driver?
>
> James
>



-- 
+-=====---------------------------+
| +---------------------------------+ | This space intentionally blank
for notetaking.
| |   | Daniel Castro,                |
| |   | Consultant/Programmer.|
| |   | U Andes                         |
+-------------------------------------+

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