[dpdk-dev] [PATCH v13 2/2] vhost: Add VHOST PMD

[Tetsuya Mukawa]

On 2016/03/22 0:40, Loftus, Ciara wrote:
>> +
>> +static void
>> +eth_dev_info(struct rte_eth_dev *dev,
>> +         struct rte_eth_dev_info *dev_info)
>> +{
>> +    dev_info->driver_name = drivername;
>> +    dev_info->max_mac_addrs = 1;
>> +    dev_info->max_rx_pktlen = (uint32_t)-1;
>> +    dev_info->max_rx_queues = dev->data->nb_rx_queues;
>> +    dev_info->max_tx_queues = dev->data->nb_tx_queues;
> I'm not entirely familiar with eth driver code so please correct me if I am 
> wrong.
>
> I'm wondering if assigning the max queue values to dev->data->nb_*x_queues is 
> correct.
> A user could change the value of nb_*x_queues with a call to 
> rte_eth_dev_configure(n_queues) which in turn calls 
> rte_eth_dev_*x_queue_config(n_queues) which will set dev->data->nb_*x_queues 
> to the value of n_queues which can be arbitrary and decided by the user. If 
> this is the case, dev->data->nb_*x_queues will no longer reflect the max, 
> rather the value the user chose in the call to rte_eth_dev_configure. And the 
> max could potentially change with multiple calls to configure. Is this 
> intended behaviour?

Hi Ciara,

Thanks for reviewing it. Here is a part of rte_eth_dev_configure().

int
rte_eth_dev_configure(uint8_t port_id, uint16_t nb_rx_q, uint16_t nb_tx_q,
                      const struct rte_eth_conf *dev_conf)
{
        <snip>
        /*
         * Check that the numbers of RX and TX queues are not greater
         * than the maximum number of RX and TX queues supported by the
         * configured device.
         */
        (*dev->dev_ops->dev_infos_get)(dev, &dev_info);

        if (nb_rx_q == 0 && nb_tx_q == 0) {
               <snip>
                return -EINVAL;
        }

        if (nb_rx_q > dev_info.max_rx_queues) {
               <snip>
                return -EINVAL;
        }

        if (nb_tx_q > dev_info.max_tx_queues) {
               <snip>
                return -EINVAL;
        }

        <snip>

        /*
         * Setup new number of RX/TX queues and reconfigure device.
         */
        diag = rte_eth_dev_rx_queue_config(dev, nb_rx_q);
        <snip>
        diag = rte_eth_dev_tx_queue_config(dev, nb_tx_q);
        <snip>
}

Anyway, rte_eth_dev_tx/rx_queue_config() will be called only after
checking the current maximum number of queues.
So the user cannot set the number of queues greater than current maximum
number.

Regards,
Tetsuya