Re: [Xen-devel] [PATCH v5 09/13] xen/pvcalls: implement sendmsg

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 17 Oct 2017, Boris Ostrovsky wrote:
> > +static int __write_ring(struct pvcalls_data_intf *intf,
> > +                   struct pvcalls_data *data,
> > +                   struct iov_iter *msg_iter,
> > +                   int len)
> > +{
> > +   RING_IDX cons, prod, size, masked_prod, masked_cons;
> > +   RING_IDX array_size = XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER);
> > +   int32_t error;
> > +
> > +   error = intf->out_error;
> > +   if (error < 0)
> > +           return error;
> > +   cons = intf->out_cons;
> > +   prod = intf->out_prod;
> > +   /* read indexes before continuing */
> > +   virt_mb();
> > +
> > +   size = pvcalls_queued(prod, cons, array_size);
> > +   if (size >= array_size)
> > +           return 0;
> 
> 
> I thought you were going to return an error here? If this can only be
> due to someone messing up indexes is there a reason to continue trying
> to write? What are the chances that the index will get corrected?

Sorry, I forgot. I'll change it to return an error, maybe EFAULT.


> > +   if (len > array_size - size)
> > +           len = array_size - size;
> > +
> > +   masked_prod = pvcalls_mask(prod, array_size);
> > +   masked_cons = pvcalls_mask(cons, array_size);
> > +
> > +   if (masked_prod < masked_cons) {
> > +           copy_from_iter(data->out + masked_prod, len, msg_iter);
> > +   } else {
> > +           if (len > array_size - masked_prod) {
> > +                   copy_from_iter(data->out + masked_prod,
> > +                                  array_size - masked_prod, msg_iter);
> > +                   copy_from_iter(data->out,
> > +                                  len - (array_size - masked_prod),
> > +                                  msg_iter);
> > +           } else {
> > +                   copy_from_iter(data->out + masked_prod, len, msg_iter);
> > +           }
> > +   }
> > +   /* write to ring before updating pointer */
> > +   virt_wmb();
> > +   intf->out_prod += len;
> > +
> > +   return len;
> > +}
> 

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