[dpdk-dev] How to replace rte_eth_dev_attach with rte_eal_hotplug_add

[Thomas Monjalon]

21/09/2018 09:19, Hideyuki Yamashita:
> Dear Gaetan and Thomas, 
> 
> Thanks for your answer.
> Please see inline.
> 
> > 20/09/2018 11:09, Ga�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.

You can have a race condition.
>
> 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?	

This function works only if you know the ethdev name generated by the PMD.

> 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.

If you want the ethdev port ids created after probing (based on devargs),
you probably want to request it with the same devargs.
I will try to work on something for this need.
For now, the most reliable solution is to use the notifications.

> > 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?

Yes, look at these ones:
    RTE_ETH_EVENT_NEW,      /**< port is probed */
    RTE_ETH_EVENT_DESTROY,  /**< port is released */

> If there are code in example, it is highly appreciated.

You can register a callback with
	rte_eth_dev_callback_register(RTE_ETH_ALL, RTE_ETH_EVENT_NEW, ...)
like done in drivers/net/failsafe/failsafe.c