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SubjectRe: [PATCH v5 09/13] xen/pvcalls: implement sendmsg
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> +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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