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 Thomas and all,

About a month ago, I posted the topic related with 
how to replace rte_eth_dev_attach.

Following your advice,
my code would be as below:
(Old code using deprecated API is commented out)

rte_eth_dev_get_port_by_name is used to retrieve dpdk port
after rte_eal_hotplug_add.
Note that my application is just one of the dpdk applications(in the host)
and within the process, only one thread handles device attatch/detach.
(No race condition with regard to device hot_plug will
not take place)
-------------------------------------------------------------------
        //ret = rte_eth_dev_attach(devargs, &vhost_port_id);
        //if (ret < 0)
        //      return ret;

        struct rte_devargs da;

        memset(&da, 0, sizeof(da));

        /* parse devargs */
        if (rte_devargs_parse(&da, devargs))
                return -1;
        ret = rte_eal_hotplug_add(da.bus->name, da.name, da.args);
        if (ret < 0) {
                free(da.args);
                return ret;
        }
        free(da.args);
        ret = rte_eth_dev_get_port_by_name(da.name, &vhost_port_id);
        if (ret < 0)
                return ret;
-----------------------------------------------------------------------------

If you have any concerns/additional advices, please let me know.

BR,
Hideyuki Yamashita
NTT TechnoCross


> 27/09/2018 12:40, Hideyuki Yamashita:
> > Dear Thomas,
> > 
> > Thansk for your answer.
> > Please see inline.
> > 
> > > 27/09/2018 03:38, Hideyuki Yamashita:
> > > > Dear Thomas,
> > > > 
> > > > Thanks for your answer.
> > > > It took me a little time to digest answer.
> > > > Please see inline.
> > > > 
> > > > 
> > > > > 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.
> > > > Please elaborate me a bit more.
> > > > 
> > > > Is it correct understanding that race condition 
> > > > includes
> > > > - read information before port is available
> > > > - other device may be plugged (or unplugged)
> > > > and so using "eth_dev_last_created_port" is 
> > > > NOT reliable?
> > > 
> > > I am thinking about the second one only.
> > 
> > If we assume there is only one DPDK application 
> > inside the host and within the application, only one thread
> > handles attach/detach of devices, then is it ok to use 
> > > > > > *port_id = eth_dev_last_created_port;
> > because there seems no possiblity race condition
> > takes place?
> 
> If you are never probing a new port outside of this thread,
> I guess it's OK.
> Take care of not attaching from the interrupt thread too!
> 
>