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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

> +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?

-boris

> +     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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