Re: [net-next-2.6 PATCH 0/6 v4] macvlan: MAC Address filtering support for passthru mode

On 11/18/2011 9:40 AM, Ben Hutchings wrote:

On Fri, 2011-11-18 at 08:58 -0800, Greg Rose wrote:

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On 11/17/2011 4:44 PM, Ben Hutchings wrote:

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On Thu, 2011-11-17 at 16:32 -0800, Greg Rose wrote:

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On 11/17/2011 4:15 PM, Ben Hutchings wrote:

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Sorry to come to this rather late.

On Tue, 2011-11-08 at 23:55 -0800, Roopa Prabhu wrote:
[...]

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v2 ->    v3
- Moved set and get filter ops from rtnl_link_ops to netdev_ops
- Support for SRIOV VFs.
           [Note: The get filters msg (in the way current get rtnetlink handles
           it) might get too big for SRIOV vfs. This patch follows existing sriov
           vf get code and tries to accomodate filters for all VF's in a PF.
           And for the SRIOV case I have only tested the fact that the VF
           arguments are getting delivered to rtnetlink correctly. The code
           follows existing sriov vf handling code so rest of it should work fine]

[...]

This is already broken for large numbers of VFs, and increasing the
amount of information per VF is going to make the situation worse.  I am
no netlink expert but I think that the current approach of bundling all
information about an interface in a single message may not be
sustainable.

Also, I'm unclear on why this interface is to be used to set filtering
for the (PF) net device as well as for related VFs.  Doesn't that
duplicate the functionality of ndo_set_rx_mode and
ndo_vlan_rx_{add,kill}_vid?

Functionally yes but contextually no.  This allows the PF driver to know
that it is setting these filters in the context of the existence of VFs,
allowing it to take appropriate action.  The other two functions may be
called without the presence of SR-IOV enablement and the existence of VFs.

Anyway, that's why I asked Roopa to add that capability.

I don't follow.  The PF driver already knows whether it has enabled VFs.

How do filters set this way interact with filters set through the
existing operations?  Should they override promiscuous mode?  None of
this has been specified.

Promiscuous mode is exactly the issue this feature is intended for.  I'm
not familiar with the solarflare device but Intel HW promiscuous mode is
only promiscuous on the physical port, not on the VEB.  So a packet sent
from a VF will not be captured by the PF across the VEB unless the MAC
and VLAN filters have been programmed into the HW.

Yes, I get it.  The hardware bridge needs to know more about the address
configuration on the host than the driver is getting at the moment.

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So you may not need
the feature for your devices but it is required for Intel devices.

Well we don't have the hardware bridge but that means each VF driver
needs to know whether to fall back to the software bridge.  The net
driver needs much the same additional information.

quoted

And
it's a fairly simple request, just allow -1 to indicate that the target
of the filter requests is for the PF itself.  Using the already existing
set_rx_mode function wont' work because the PF driver will look at it
and figure it's in promiscuous mode anyway, so it won't set the filters
into the HW.  At least that is how it is in the case of our HW and
driver.  Again, the behavior of your HW and driver is unknown to me and
thus you may not require this feature.

What concerns me is that this seems to be a workaround rather than a fix
for over-use of promiscuous mode, and it changes the semantics of
filtering modes in ways that haven't been well-specified.

I feel the opposite is true.  It allows a known set of receive filters 
so that you don't have to use promiscuous mode, which cuts down on 
overhead from processing packets the upper layer stack isn't really 
interested in.

What if there's a software bridge between two net devices corresponding
to separate physical ports, so that they really need to be promiscuous?
What if the administrator runs tcpdump and really wants the (PF) net
device to be promiscuous?

I don't believe there is anything in this patch set that removes 
promiscuous mode operation as it is commonly used.  Perhaps I've missed 
something.

These cases shouldn't break because of VF acceleration.

I don't see how they would in the case of Intel HW.  And these new ops 
to set rx filters are something that Intel HW needs because it 
implements a VEB that is *not* a learning bridge and we don't want it to 
be a learning bridge because of security concerns.  It is better for our 
requirements to be allowed to set the MAC/VLAN filters that we want a VF 
to be able to see.

Or at least we
should make a conscious and documented decision that 'promiscuous'
doesn't mean that if you enable it on your network adapter.

Again, I don't know of any plans to change anything relating to putting 
a device in promiscuous mode or changing the semantics of what 
promiscuous mode means.

- Greg