linux-kernel - Re: [PATCH v5 09/13] xen/pvcalls: implement sendmsg

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Date:   Thu, 19 Oct 2017 18:41:47 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org,
        jgross@...e.com, Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v5 09/13] xen/pvcalls: implement sendmsg

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;
> > +}
>