Re: [dpdk-dev] [PATCH v2] net/pcap: enable data path on secondary

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 11/12/2018 4:51 PM, Qi Zhang wrote:
> Private vdev on secondary is never supported by the new shared
> device mode but pdump still relies on a private pcap PMD on secondary.
> The patch enables pcap PMD's data path on secondary so that pdump can
> work as usual.

It would be great if you described the problem a little more.

Private vdev was the way previously, when pdump developed, now with shared
device mode on virtual devices, pcap data path in secondary is not working.

What exactly not working is (please correct me if I am wrong):
When secondary adds a virtual device, related data transferred to primary and
primary creates the device and shares device back with secondary.
When pcap device created in primary, pcap handlers (pointers) are process local
and they are not valid for secondary process. This breaks secondary.

So we can't directly share the pcap handlers, but need to create a new set of
handlers for secondary, that is what you are doing in this patch, although I
have some comments, please check below.

Since there is single storage for pcap handlers that primary and secondary
shares and they can't share the handlers, you can't make both primary and
secondary data path work. Also freeing handlers is another concern. What is
needed is `rte_eth_dev->process_private` which has been added in this release.

> 
> Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>
> Tested-by: Yufeng Mo <yufengx.mo@intel.com>

<...>

> @@ -934,6 +935,10 @@ pmd_init_internals(struct rte_vdev_device *vdev,
>  	 */
>  	(*eth_dev)->dev_ops = &ops;
>  
> +	/* store a copy of devargs for secondary process */
> +	strlcpy(internals->devargs, rte_vdev_device_args(vdev),
> +			ETH_PCAP_ARG_MAXLEN);

Why we need to cover this in PMD level?

Why secondary probe isn't getting devargs? Can't we fix this in eal level?
It can be OK to workaround in the PMD taking account of the time of the release,
but for long term I think this should be fixed in eal.

<...>

> @@ -1122,23 +1126,37 @@ pmd_pcap_probe(struct rte_vdev_device *dev)
>  	start_cycles = rte_get_timer_cycles();
>  	hz = rte_get_timer_hz();
>  
> -	if (rte_eal_process_type() == RTE_PROC_SECONDARY) {
> +	if (rte_eal_process_type() == RTE_PROC_PRIMARY) {
> +		kvlist = rte_kvargs_parse(rte_vdev_device_args(dev),
> +				valid_arguments);
> +		if (kvlist == NULL)
> +			return -EINVAL;
> +		if (rte_kvargs_count(kvlist, ETH_PCAP_IFACE_ARG) == 1)
> +			nb_rx_queue = 1;
> +		else
> +			nb_rx_queue =
> +				rte_kvargs_count(kvlist,
> +					ETH_PCAP_RX_PCAP_ARG) ? 1 : 0;
> +		nb_tx_queue = 1;

This part is wrong. pcap pmd supports multi queue, you can't hardcode the number
of queues. Also for Tx why it ignores `rx_iface` argument?
This is just hacking the driver for a specific use case breaking others.

> +		ret = pmd_init_internals(dev, nb_rx_queue,
> +				nb_tx_queue, &eth_dev);

I think it is not required to move pmd_init_internals() here.
This can be done simpler, I will send a draft patch as a reply to this mail for
possible solution.
But again that can't be final solution, we need to use `process_private`

<...>