Can DPDK selectively init NIC ports

I'm using an dual-port NIC, Mellanox ConnectX-5, and the DPDK version is dpdk-stable-19.11.3. After configuration, the call of rte_eth_dev_count_avail() returns 2. But only one port of my ConnectX-5 NIC is connected to the other machine. All I can find is to init all available ports like this.

RTE_ETH_FOREACH_DEV(portid)
    if (port_init(portid, mbuf_pool) != 0)
        rte_exit(EXIT_FAILURE, "Cannot init port %u\n", portid);

Can dpdk selectively init ports? Or is there any way to make rte_eth_dev_count_avail() returning 1?

Yes one can selectively init ports by passing the right PCIe Bus:Device:Function address as a whitelist. Hence only desired ports will pop up in the application.

How to do it:

1. create a dummy application to take in all DPDK port.
2. Initialize and start the dpdk ports. Check for link-state and create port-mask (global variable) which filters in application logic.
3. Invoke rte_eth_dev_stop & rte_eth_dev_close for link down ports.
4. Invoke rte_eal_cleanup.
5. Use the port-mask, as an argument for execv to invoke your desired DPDK application.

this way you can run your application with valid ports to it.

But relying on rte_eth_link_get is tricky because

• if the other end is connected to dpdk-pktgen, first your DPDK application has to init the NIC locally.
• if connected to linux box, the nic has to be bought up first with ifconfig [other nic] up
• at times one needs to check link.link_speed if its valid.
• certain PMD needs write to PCIe mapped register, hence has to dev_configure and port_init to get a reliable reading for link status.

Hence safest and recommended way to use is identify the NIC PCIe B:D:F in Linux driver and then whitelist the ports by using option -w for the desired port under igb_uio/virtio-pci. This can be done by bind all NIC back in linux by

1. lshw -c network -businfo will list NIC and PCIe Bus:Device:Function with kerel device name and driver.
2. use ethtool [eth device name] | grep Link to identify the link is connected.

for reference, you can use https://github.com/vipinpv85/DPDK-APP_SAMPLES/blob/master/auto-baseaddr-selector.c as template for dummy applciation.