Re: [dpdk-dev] [PATCH] doc: document the new devargs syntax

[Yuanhan Liu <yliu@fridaylinux.org>]

On Thu, Jan 18, 2018 at 10:46:23AM +0100, Gaëtan Rivet wrote:
> On Thu, Jan 18, 2018 at 09:46:29AM +0100, Thomas Monjalon wrote:
> > 18/01/2018 08:35, Yuanhan Liu:
> > > On Wed, Jan 17, 2018 at 12:34:08PM +0000, Ferruh Yigit wrote:
> > > > So does it make sense to separate them logically? Perhaps as "device identifier"
> > > > and "device args".
> > > 
> > > Then I think it returns back to the old issue: how could we identify a
> > > port when the bus id (say BDF for PCI bus) is not enough for identifying
> > > a port? Such case could happen when a single NIC has 2 ports sharing
> > > the same BDF. It could also happen with the VF representors that will
> > > be introduced shortly.
> > 
> > Yes, the device matching syntax must include bus category, class category
> > and driver category. So any device can be identified in future.
> > 
> > But I think Ferruh is talking about separating device matching
> > (which is described in this proposal) and device settings
> > (which are usually mixed in -w and --vdev options).
> > I agree there are different things and may be separate.
> > They could share the same syntax (bus/class/driver) but be separate
> > with a semicolon:
> > 	matching;settings
>
> Can you give an example?

Let's take port addition in OVS-DPDK as an example. It happens in 2
steps:
- port lookup (if port is already probed)
- dev attachment (if lookup fails)

And also let's assume we need probe a ConnectX-3 port. Note that for
ConnectX-3, there are 2 ports sharing the same PCI addr. Thus, PCI
BDF is not enough. And let's assume we use another extra property
"port".

If the proposal described in this patch is being used, the devarg
would look like following:

    bus=pci,id=04:00.0/class=eth,port=0/driver=mlx4,mlx4_arg_A=val,...

Then "bus=pci,id=04:00.0/class=eth,port=0" will be used for lookup,
It means we are looking for a port with PCI BDF == 04:00.0 AND
port == 0 (the first port of the 2 ports).

Note that in my proposal the driver category is not intended for lookup.
If any properties needed be looked in the driver category, they would
probably need be elevated to the class category.

If port not found, then the whole string will be used for dev attachment.
It means we are attaching a port with PCI BDF == 04.00.0 AND
port == 0 (the 2nd port will not be attached).


And here is how the devargs would look like if "matching;settings" is
being used:

    bus=pci,id=04:00.0/class=eth,port=0;bus=pci,id=04:00.0/class=eth,port=0/driver=mlx4,mlx4_arg_A=val,...

The part before ";" will be used for lookup and the later part will be
used for attachment. It should work. It just looks redundant.

	-yliu