Re: [PATCH] net/tap: Bug fix to populate fds in secondary process

[kumaraparameshwaran rathinavel <kumaraparamesh92@gmail.com>]

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Just wanted to bring it to your attention,

In Mellanox driver there is a requirement to exchange fds between primary
and secondary and similar usage is seen, the primary sends the port_id and
the secondary refers to the rte_eth_devices in the driver,
The functions are
           - mlx5_mp_secondary_handle in secondary
           - mlx5_mp_req_start_rxtx in primary which is invoked from
mlx5_dev_start.

In my implementation I have used the name and invoked get_port_by_name, I
can also pass the port_id from the primary to make it uniform. So with
similar usage in Mellanox is there a problem there as well on referring to
the rte_eth_devices from the PMD ?


On Tue, Jan 18, 2022 at 3:17 PM Ferruh Yigit <ferruh.yigit@intel.com> wrote:

> On 1/17/2022 6:33 PM, Thomas Monjalon wrote:
> > 17/01/2022 19:28, Ferruh Yigit:
> >>> +   ret = rte_eth_dev_get_port_by_name(request_param->port_name,
> &port_id);
> >>> +   if (ret) {
> >>> +           TAP_LOG(ERR, "Failed to get port id for %s",
> >>> +                   request_param->port_name);
> >>> +           return -1;
> >>> +   }
> >>> +   dev = &rte_eth_devices[port_id];
> >>
> >> Since this is not really related with your patch, I want to have a
> separate thread for it.
> >>
> >> It is not good to access the 'rte_eth_devices' global variable directly
> from a driver, that
> >> is error prone.
> >>
> >> Btw, what 'peer' supposed to contain?
> >>
> >> It can be solved by adding an internal API, only for drivers to get
> eth_dev from the name,
> >> like: 'rte_eth_dev_get_by_name()'.
> >> This way a few other usage can be converted to this API.
> >>
> >> @Thomas and @Andrew what do you think about the new API proposal?
> >
> > It looks similar to rte_eth_dev_get_port_by_name() which returns a
> port_id.
>
> Exactly, but get eth_dev directly for drivers. For drivers no need to work
> with port_id
> handler, they can use eth_dev directly.
>
> Another solution can be an getter function for drivers, which gets port_id
> and returns
> the eth_dev.
>
> > It is a bit strange for an ethdev driver to not have access to its own
> ethdev struct.
> > Isn't there something broken in the logic?
> >
>
> This is callback function between primary and secondary applications sync.
> So port name
> will be same for both, but eth_dev will be different and port_id may be
> different.
> Driver finds its own eth_dev from the shared port name.
>
>

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