Re: [dpdk-dev] [PATCH v2] examples/client_server_mp: check port ownership

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 8 Jul 2019 06:37:14 +0000
Matan Azrad <matan@mellanox.com> wrote:

> Hi Stephen
> 
> From: Stephen Hemminger 
> > Sent: Sunday, July 7, 2019 7:47 PM
> > To: Matan Azrad <matan@mellanox.com>
> > Cc: anatoly.burakov@intel.com; dev@dpdk.org; Stephen Hemminger
> > <sthemmin@microsoft.com>
> > Subject: Re: [dpdk-dev] [PATCH v2] examples/client_server_mp: check port
> > ownership
> > 
> > On Sun, 7 Jul 2019 05:44:55 +0000
> > Matan Azrad <matan@mellanox.com> wrote:
> >   
> > > > +	for (count = 0; pm != 0; pm >>= 1, ++count) {
> > > > +		struct rte_eth_dev_owner owner;
> > > > +
> > > > +		if ((pm & 0x1) == 0)
> > > > +			continue;
> > > > +
> > > > +		if (count >= max_ports) {
> > > > +			printf("WARNING: requested port %u not present -
> > > > ignoring\n",
> > > > +				count);
> > > > +			continue;
> > > > +		}
> > > > +		if (rte_eth_dev_owner_get(count, &owner) < 0) {
> > > > +			printf("ERROR: can not find port %u owner\n",
> > > > count);  
> > >
> > > What if some entity will take ownership later?
> > > If you want the app will be ownership aware:
> > > 	if you sure that you want this port to be owned by this application  
> > you need to take ownership on it.  
> > > else:
> > > the port is hidden by RTE_ETH_FOREACH_DEV if it is owned by some entity.
> > > see how it was done in testpmd function: port_id_is_invalid().  
> > 
> > There are no mysterious entities in DPDK.
> > The only thing that can happen later is hotplug, and that will not change state
> > of existing port.
> > This model is used for all applications.  The application does not take
> > ownership, only device drivers do.  
> 
> A long discussions were done on it.
> There is an application model to take ownership as I wrote you above.
> You chose in the second option - not to be ownership aware.
>  
> From docs:
> "10.4.2. Port Ownership
> The Ethernet devices ports can be owned by a single DPDK entity (application, library, PMD, process, etc). The ownership mechanism is controlled by ethdev APIs and allows to set/remove/get a port owner by DPDK entities. Allowing this should prevent any multiple management of Ethernet port by different entities.
> 
> Note
> 
> It is the DPDK entity responsibility to set the port owner before using it and to manage the port usage synchronization between different threads or processes."
> 
> > The whole portmask as command-line parameter is a bad user experience
> > now, but that is a different problem.  
> 
> I think, this is the problem you should solve here.

No other application is doing this: testpmd, l3fwd, ... why do you think
this application is different. Plus you would be putting a new requirement on
all the user applications. That would be a user hostile change.