Re: [dpdk-dev] How to replace rte_eth_dev_attach with rte_eal_hotplug_add

[Hideyuki Yamashita <yamashita.hideyuki@po.ntt-tx.co.jp>]

Dear Gaetan and Thomas, 

Thanks for your answer.
Please see inline.

> 20/09/2018 11:09, Ga枓an Rivet:
> > On Thu, Sep 20, 2018 at 05:46:37PM +0900, Hideyuki Yamashita wrote:
> > > Hello,
> > > 
> > > From dpdk 18.08 release rte_eth_dev_attach and 
> > > rte_eth_dev_detach becom deprecated API and 
> > > it is recommended to replace with rte_eal_hotplug_add
> > > and rte_eal_hotplug_remove.
> > > 
> > > My program uses  above mentioned deprecated APIs
> > > and have to replace those.
> > > Note that my program uses attach to attach vhost, pcap pmd.
> > > 
> > > My question is whether it is correct to replace those as following:
> > > find rte_eth_dev_attach function in rte_ethdev.c and
> > > migrate those content into my program.
> > > 
> > > e.g. 
> > > lib/librte_ethdev/rte_ethdev.c line 643-686 for attach
> > > lib/librte_ethdev/rte_ethdev.c line 690-720 for detach
> > > 
> > > Your advice/guidance are much appreciated.
> > > Thanks!
> > 
> > Hello Hideyuki,
> > 
> > You could use this code for guidance, while leaving the ethdev
> > specificities such as verifying the eth_dev_count_total(). The hotplug
> > function would already return an error if the PMD was not able to create
> > the necessary devices.
> > 
> > The main issue might be to find the port_id of your new port.
> > You won't be able to use eth_dev_last_created_port, so you would have to
> > iterate over the ethdev using RTE_ETH_FOREACH_DEV and find the one
> > matching your parameters (you might for example match the rte_device
> > name with the name you used in hotplug_add, as there is no standard
> > naming scheme at the ethdev level).
First of all, thank for your answering to my question.
But I have questions.
(Sorry, I have poor knowledge about dpdk and have many basic questions)

Q1. 
Why eth_dev_last_created_port can not be used?
When I look into rte_eth_dev_atthach in 18.08, it calls 

*port_id = eth_dev_last_created_port;

at the end of the function.
 
Q2. 
Is it possible to use rte_eth_dev_get_port_by name 
instead of calling RTE_ETH_FOREACH_DEV or using
eth_dev_last_created_port?	

Q3. 
If answer to Q2 is no, then how can I get device name from each device?
For example, rte_eth_dev_info_get takes port_id as its
argument.But what I want to know is the port id of the specified device
name.

> It is recommended to register a callback to receive the notifications
> of new ethdev ports.
> So it may be a change of programming style: sync vs async.
Thanks for your advice.
In general, I agree.

But what is the example of notification that program can receive
after device hotplugged?
Device unplugged notification like specified in rte_eth_event_type?
If there are code in example, it is highly appreciated.

> > An possible issue with the deprecation planned for those two functions is
> > that the hotplug API is also meant to evolve [1] this release (not in a big
> > way however, it would mostly simplify your usage of it).
> > 
> > [1]: https://mails.dpdk.org/archives/dev/2018-September/111142.html
> 
> I will probably not change the existing functions.
> A v2 will be sent soon, with new simple functions.
> 
> 
> 

BR,
Hideyuki Yamashita
NTT TechnoCross