Re: [Qemu-devel] [PATCH v3 2/2] net: introduce command to query rx-filter information

[Amos Kong]

On Fri, Jul 12, 2013 at 08:32:29AM +0200, Markus Armbruster wrote:
> Amos Kong <address@hidden> writes:
> 
> > On Thu, Jul 04, 2013 at 08:28:59AM +0200, Markus Armbruster wrote:
> >> Amos Kong <address@hidden> writes:
> >> 
> >> > On Tue, Jul 02, 2013 at 03:27:12PM +0200, Markus Armbruster wrote:
> >> >> Amos Kong <address@hidden> writes:
> >> >> 
> >> >> > On Tue, Jul 02, 2013 at 11:05:56AM +0200, Markus Armbruster wrote:
> >> >> >> Amos Kong <address@hidden> writes:
> >> >> [...]
> >> >> >> >> This interface is abstract in the sense that it applies to
> >> >> >> >> all NICs.  At
> >> >> >> >> this time, it's implemented only virtio-net implements it.  I'm
> >> >> >> >> habitually wary of abstractions based on just one concrete 
> >> >> >> >> instance,
> >> >> >> >> which makes me ask:
> >> >> >> >> 
> >> >> >> >> 1. Ignorant question first: could the feature make sense
> >> >> >> >> for other NICs,
> >> >> >> >> too, or is it specific to virtio-net?
> >> >> >> >
> >> >> >> > We will not. 
> >> >> >> >
> >> >> >> > It's ugly to check if nic is virtio-net nic in net/net.c, so I
> >> >> >> > register the query function to NetClientInfo. Traversal the net
> >> >> >> > client list in net/net.c, and execute query of each virtio-net
> >> >> >> > instance in virtio-net.c
> >> >> >> 
> >> >> >> Implementing the feature as an optional callback is fine.
> >> >> >> 
> >> >> >> Let me rephrase my question: could this feature be implemented for 
> >> >> >> other
> >> >> >> NICs?  I'm *not* asking you to do that, just whether it would be
> >> >> >> possible.
> >> >> >> 
> >> >> >> I'm asking because my review of the QAPI schema depends on the 
> >> >> >> answer.
> >> >> >> 
> >> >> >> >> 2. If the former, are you reasonably sure this object will
> >> >> >> >> do for other
> >> >> >> >> NICs?
> >> >> >> >
> >> >> >> > No.
> >> >> >> 
> >> >> >> I'm not sure I understand you.  Do you mean to say that the feature
> >> >> >> could be implemented for other NICs, but RxFilterInfo would probably 
> >> >> >> not
> >> >> >> fit for them?
> >> >> >
> >> >> > We will not implement the feature to other NICs, no request.
> >> >> >
> >> >> > We notify the management of virtio-net rx-filter change, because
> >> >> > we want to sync the the rx-filter change to macvtap device.
> >> >> 
> >> >> I understand there are no plans to implement this feature for other
> >> >> NICs.  But I'm not asking whether we *want* to implement it for other
> >> >> NICs, I'm asking whether we *could*.
> >> >  
> >> > In theory, we can.
> >> >
> >> >> Or rephrased yet another way: what exactly makes this feature applicable
> >> >> to virtio-net only?
> >> >
> >> > Macvtap can only be used by virtio-net, not other emulated nic.
> >> > It's meaningless for management to know the rx-filter change of
> >> > non-virtio-net NICs.
> >> 
> >> I'm having trouble squaring "in theory, we can" with "meaningless".  So
> >> I'm rephrasing my question yet again.
> >> 
> >> Do NICs other than virtio-net have rx-filters?
> >  
> > Yes.
> >
> > Talked with Jason, upstream kernel fixed some bugs, then we can also
> > use e1000 with macvtap. In this case, we should also implement a
> > .query_rx_filter function for e1000. We can do it by another patchset.
> 
> Yes.  Just to avoid misunderstandings: I'm not asking you for that.  I
> merely asked whether it's possible, and you answered that.
> 
> >> If yes, what have these NIC rx-filters in common, and how do they
> >> differ?
> >> 
> >> Why would anybody want to query rx-filters?  Use cases, please.
> >
> > It's a way to tell management the rx-filter setup in guest nic.
> > Management query the rx-filter setup of guest, then change the
> > setup of macvtap device, macvtap uses same rx-filter setup as
> > virtual nic.
> 
> So this use case is "mirror the virtual NIC's rx-filter setup to
> macvtap".  Makes sense.
> 
> This leads me to the question I've been aiming for all along: will your
> definition of RxFilterInfo do for devices other than virtio-net?
 
query_rx_filter() returns the address of nic's RxFilterInfo.
RxFilterInfo is general.

> It should do if it contains only stuff that all NICs with an rx-filter
> have.  Is that the case?

Yes.

-- 
                        Amos.