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

[Thomas Monjalon <thomas@monjalon.net>]

Just a quick comment:
There are probably some ideas to take from what was done for tap.


13/11/2018 17:56, Ferruh Yigit:
> 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`
> 
> <...>
>