Re: [PATCH] [RFC] ether: standardize getting the port by name

[Thomas Monjalon <thomas@monjalon.net>]

05/12/2017 12:04, Adrien Mazarguil:
> Hi Yuanhan,
> 
> On Mon, Dec 04, 2017 at 09:55:31PM +0800, Yuanhan Liu wrote:
> > rte_devargs is identified by the name (pci id for pci device). It also
> > includes other driver specific key-value options. It's not clear for the
> > user to know which one (or few) of them should be used together with the
> > PCI id to identify a specific port. For example, as you mentioned, in
> > mlx4, it's "pci_id,port=x". It could be something else in other drivers.
> 
> Just for information, this "port=x" argument in mlx4 is consistent with the
> value found in /sys/class/net/ethX/dev_port under Linux. If we choose to use
> a port index (instead of a MAC or something else), it would make sense to
> standardize it on the same order as given by the host OS for consistency
> across all PMDs.

Good idea, thanks.

I think we will MAC in some cases and port number in others.
It is important to have identifiers available even without initializing
the device.

> Devices with a single port per PCI address would simply use/allow "0".
> 
> > Actually, this patch also proposes a devarg like naming style: "name[,mac]".
> > What it does try to do is to define a standard syntax, so that the user
> > doesn't have to know any driver specific options.
> > 
> > However, the mac address is changeable, leaving this naming inconsistent.
> > Well, in practice, PCI id is also changeable.
> > 
> > OTOH, having a consistent naming seems a bit far away from this patch's
> > goal: define a standard ethdev naming and leave less harassment to the users.
> 
> I'm not a fan of the MAC naming scheme either, a kind of per-device physical
> port index seems more robust and doesn't require much initialization to
> determine how many ports are supported by the device and whether the index is
> known/valid (particularly given the vast majority exposes only one per bus
> address).
> 
> Would it make sense to have this name usable unmodified as a valid device
> (-w) argument, including parameters?

Yes we must provide some new key/value arguments for devargs.
So it can be used anywhere, including -w/-b options in DPDK
or port configuration in OVS.

> If so, PMDs could append parameters while probing the underlying device, by
> appending ",port=x", ",mac=x" followed by other unspecified parameters with
> default values. This could uniquely identify the port _and_ its
> configuration in a reusable fashion.

Question: should we separate device identification and configuration
in the syntax?

> Otherwise if all we need is unique names, we can use the opposite and much
> simpler approach. Let librte_ether assign them sequentially
> (e.g. "rte_eth%d", no need for consistency with OS netdevices), applications
> can figure the rest based on data structures if needed.

No, unique names are not useful / not usable by users.