Re: [Xen-devel] [PATCH v4 09/13] xen/pvcalls: implement sendmsg

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

> +static bool pvcalls_front_write_todo(struct sock_mapping *map)
> +{
> +     struct pvcalls_data_intf *intf = map->active.ring;
> +     RING_IDX cons, prod, size = XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER);
> +     int32_t error;
> +
> +     cons = intf->out_cons;
> +     prod = intf->out_prod;
> +     error = intf->out_error;
> +     if (error == -ENOTCONN)
> +             return false;
> +     if (error != 0)
> +             return true;

Just like below, error processing can be moved up.

> +     return !!(size - pvcalls_queued(prod, cons, size));
> +}
> +
>  static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
>  {
>       struct xenbus_device *dev = dev_id;
> @@ -363,6 +380,108 @@ int pvcalls_front_connect(struct socket *sock, struct 
> sockaddr *addr,
>       return ret;
>  }
>  
> +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;


Is it possible to have size > array_size?


> +     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;


I know that you said you'd be changing len's type to int but now that I
am looking at it I wonder whether you could pass len as a 'size_t *' and
have this routine return error code (i.e. <=0).

OTOH, we'd be mixing up types again since RING_IDX is an unsigned int.

So I'll leave it to you (or anyone else reviewing this) to decide which
way is better.


> +}
> +
> +int pvcalls_front_sendmsg(struct socket *sock, struct msghdr *msg,
> +                       size_t len)

Also, the signature here looks suspicious --- you are trying to send
'size_t len' bytes but returning an int, which is how many bytes you've
actually sent. Right?


-boris


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