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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

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.)



> @@ -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?

-boris




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