linux-kernel - Re: [PATCH v4 09/13] xen/pvcalls: implement sendmsg

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Date:   Fri, 22 Sep 2017 17:57:08 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org
Cc:     linux-kernel@...r.kernel.org, jgross@...e.com,
        Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v4 09/13] xen/pvcalls: implement sendmsg


> +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