On 10/30/2013 10:34 AM, Lennert Buytenhek wrote:

On Wed, Oct 30, 2013 at 06:27:56PM +0100, Lennert Buytenhek wrote:

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This means that all per-port netdevs will be dummy ports which don't
include the data path.

And I think that's fine.

Look, even if you're not going to address data traffic to individual
ports on your switch chip, there's still a plethora of per-port
operations that you want to be able to do: administratively setting
the link state on ports up and down, controlling autonegotiation and
other PHY settings on individual ports, etc.

You can either let the administrator do this with the standard ifconfig
/ ip link / ethtool tools, or you can make up a parallel API and
corresponding set of userland tools to duplicate most of the existing
functionality -- I know which option I prefer.

Presenting each switch port as an individual Linux netdevice to the OS
is an orthogonal decision to actually using those netdevices for data
traffic, and conflating the two by arguing that you need special tools
to do per-port operations for the sole reason that your switch chip
cannot address individual ports is a rather confused argument.

Forgot to add: there's a patch for net/dsa that adds exactly such an
option.  We called it 'unmanaged' mode, and it doesn't enable packet
tagging on the CPU<->switch chip interface, so that data only ever
flows over a single network interface ("eth0"), while the other
("dummy") network interfaces ("port1", "port2", etc) are used for
setting link state with ip link, setting PHY settings with ethtool,
getting ethtool statistics, etc, with 100% unmodified userland tools.
This patch is currently buried inside a vendor tree, but I'd be happy
to dig it out and submit it.

A "dummy" network interface is something I've been thinking about
for SR-IOV as well. In the SR-IOV case we have an embedded bridge
in the hardware but the virtual functions may be direct assigned
to a guest and not visible to the host.

It would be easier to manage the ports and assign them to different
bridge/QOS objects (OVS, bridge, nftables) if the ports were visible
and manageable in the host even though there is no data path. Today
we special ndo ops that only work for VFs but this is a bit clumsy
and gets more clumsy as the nic switch becomes more like a real switch.

.John