Re: [dpdk-dev] [PATCH] ethdev: additional parameter in RX callback

["Mcnamara, John" <john.mcnamara@intel.com>]

> -----Original Message-----
> From: Neil Horman [mailto:nhorman@tuxdriver.com]
> Sent: Friday, March 13, 2015 3:09 PM
> To: Richardson, Bruce
> Cc: Mcnamara, John; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] ethdev: additional parameter in RX
> callback
> 
> Plese set asside the ABI issue for a moment.  I get that you're trying to
> get it in prior to needing to version it.  Thats not the argument.  The
> argument is how best to codify the new information you want to express in
> the callback.  For this specific case, I think there are better ways to do
> this than to just blindly add a new parameter.

Hi Neil,

I think that is good advice is the general case but this is a very specific case. The modified callback is only used in rte_eth_rx_burst(). For context here is the function in its entirety (without #defs). The substantive change (the addition of nb_pkts) is on the line with an asterisk:


    static inline uint16_t
    rte_eth_rx_burst(uint8_t port_id, uint16_t queue_id,
             struct rte_mbuf **rx_pkts, const uint16_t nb_pkts)
    {
        struct rte_eth_dev *dev;

        dev = &rte_eth_devices[port_id];

        int16_t nb_rx = (*dev->rx_pkt_burst)(dev->data->rx_queues[queue_id],
                rx_pkts, nb_pkts);

        struct rte_eth_rxtx_callback *cb = dev->post_rx_burst_cbs[queue_id];

        if (unlikely(cb != NULL)) {
            do {
                nb_rx = cb->fn.rx(port_id, queue_id, rx_pkts, nb_rx,
    *						nb_pkts, cb->param);
                cb = cb->next;
            } while (cb != NULL);
        }

        return nb_rx;
    }

> Encoding the array size
> implicitly with a terminating marker lets you use this equally well with
> the tx and rx callbacks (should you ever need it on the latter)

Is encoding the information in the array really a better solution here? The cb->param already exists for passing in user defined information to the callback. The proposed patch merely transmits the parent function arguments to the enclosed callback.

John