Re: [Xen-devel] [PATCH v2] xen/scsifront: don't request a slot on the ring until request is ready

[Juergen Gross <jgross@xxxxxxxx>]

On 05/12/16 16:32, Boris Ostrovsky wrote:
> On 12/02/2016 01:15 AM, Juergen Gross wrote:
>>  
>> -static struct vscsiif_request *scsifront_pre_req(struct vscsifrnt_info 
>> *info)
>> +static int scsifront_do_request(struct vscsifrnt_info *info,
>> +                            struct vscsifrnt_shadow *shadow)
>>  {
>>      struct vscsiif_front_ring *ring = &(info->ring);
>>      struct vscsiif_request *ring_req;
>> +    struct scsi_cmnd *sc = shadow->sc;
>>      uint32_t id;
>> +    int i, notify;
>> +
>> +    if (RING_FULL(&info->ring))
>> +            return -EBUSY;
>>  
>>      id = scsifront_get_rqid(info);  /* use id in response */
>>      if (id >= VSCSIIF_MAX_REQS)
>> -            return NULL;
>> +            return -EBUSY;
>> +
>> +    info->shadow[id] = shadow;
>> +    shadow->rqid = id;
>>  
>>      ring_req = RING_GET_REQUEST(&(info->ring), ring->req_prod_pvt);
>> -
>>      ring->req_prod_pvt++;
>>  
>> -    ring_req->rqid = (uint16_t)id;
>> +    ring_req->rqid        = id;
>> +    ring_req->act         = shadow->act;
>> +    ring_req->ref_rqid    = shadow->ref_rqid;
>> +    ring_req->nr_segments = shadow->nr_segments;
> 
> Shouldn't req_prod_pvt be incremented after you've copied everything? (I
> realize that there is not error until everything has been copied but still.)

That doesn't really matter as it is private.

>> @@ -473,44 +496,14 @@ static int map_data_for_request(struct vscsifrnt_info 
>> *info,
>>      }
>>  
>>      if (seg_grants)
>> -            ring_req->nr_segments = VSCSIIF_SG_GRANT | seg_grants;
>> +            shadow->nr_segments = VSCSIIF_SG_GRANT | seg_grants;
> 
> Are we guaranteed that seg_grants is not going to have VSCSIIF_SG_GRANT
> bit set?

Absolutely, yes. Can't be larger than VSCSIIF_SG_TABLESIZE which is 26.


Juergen

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