Re: [dpdk-dev] secondary processes and private data

[Thomas Monjalon <thomas@monjalon.net>]

Hi Alejandro,

25/09/2018 16:10, Alejandro Lucero:
> I've a problem when part of device private data needs to be private per
> process.

It appears we are facing the same issue to support multi-process in tap.

> Current multiprocess support shares device private data between primary and
> secondaries but it is all dependent on a pointer initialized to the same
> memory address by the multiprocess support code. If there is a per-process
> data, If a secondary process changes it the primary gets affected, and the
> same for additional secondaries which will affect not just the primary but
> other previous secondaries.

Yes, the field rte_eth_dev.data.dev_private is private to the device,
but shared between processes.

> The solution is to add support for this inside struct rte_eth_dev,
> something like
> 
> void *secondary_priv_data;
> 
> so it is up to the secondaries to use this field if necessary.

I would say it is not only for secondary process.
What about this name:

	rte_eth_dev.process_private

> NFP PMD creates the required rte_eth_devs specifically, similar to what is
> done inside rte_ethdev.c but adding initialization for an interface needed
> when calling device ethdev_init function. There are other PMDs doing this
> but none has this requirement for per-process private data.

Actually tap has a per-process requirement for its file descriptors.

> Please, let me know what you think about this change to struct rte_ethdev
> or if you have a better idea for solving this problem.

I support the idea, but we need to agree on name bikeshedding :-)