How network VF works with hn(4) on Hyper-V in transparent mode:
- Each network VF has a cooresponding hn(4).
- The network VF and the it's cooresponding hn(4) have the same hardware
address.
- Once the network VF is attached, the cooresponding hn(4) waits several
seconds to make sure that the network VF attach routing completes, then:
o Set the intersection of the network VF's if_capabilities and the
cooresponding hn(4)'s if_capabilities to the cooresponding hn(4)'s
if_capabilities. And adjust the cooresponding hn(4) if_capable and
if_hwassist accordingly. (*)
o Make sure that the cooresponding hn(4)'s TSO parameters meet the
constraints posed by both the network VF and the cooresponding hn(4).
(*)
o The network VF's if_input is overridden. The overriding if_input
changes the input packet's rcvif to the cooreponding hn(4). The
network layers are tricked into thinking that all packets are
neceived by the cooresponding hn(4).
o If the cooresponding hn(4) was brought up, bring up the network VF.
The transmission dispatched to the cooresponding hn(4) are
redispatched to the network VF.
o Bringing down the cooresponding hn(4) also brings down the network
VF.
o All IOCTLs issued to the cooresponding hn(4) are pass-through'ed to
the network VF; the cooresponding hn(4) changes its internal state
if necessary.
o The media status of the cooresponding hn(4) solely relies on the
network VF.
o If there are multicast filters on the cooresponding hn(4), allmulti
will be enabled on the network VF. (**)
- Once the network VF is detached. Undo all damages did to the
cooresponding hn(4) in the above item.
NOTE:
No operation should be issued directly to the network VF, if the
network VF transparent mode is enabled. The network VF transparent mode
can be enabled by setting tunable hw.hn.vf_transparent to 1. The network
VF transparent mode is _not_ enabled by default, as of this commit.
The benefit of the network VF transparent mode is that the network VF
attachment and detachment are transparent to all network layers; e.g. live
migration detaches and reattaches the network VF.
The major drawbacks of the network VF transparent mode:
- The netmap(4) support is lost, even if the VF supports it.
- ALTQ does not work, since if_start method cannot be properly supported.
(*)
These decisions were made so that things will not be messed up too much
during the transition period.
(**)
This does _not_ need to go through the fancy multicast filter management
stuffs like what vlan(4) has, at least currently:
- As of this write, multicast does not work in Azure.
- As of this write, multicast packets go through the cooresponding hn(4).
MFC after: 3 days
Sponsored by: Microsoft
Differential Revision: https://reviews.freebsd.org/D11803
Hyper-V's NIC SR-IOV implementation needs a Hyper-V synthetic NIC and
a VF NIC to work together (both NICs have the same MAC address), mainly to
support seamless live migration.
When the VF device becomes UP (or DOWN), the synthetic NIC driver needs
to switch the data path from the synthetic NIC to the VF (or the opposite).
Note: multicast/broadcast packets are still received through the synthetic
NIC and we need to inject the packets through the VF interface (if the VF is
UP), even if the synthetic NIC is DOWN (so we need to force the rxfilter
to be NDIS_PACKET_TYPE_PROMISCUOUS, when the VF is UP).
Reviewed by: sephe
Approved by: sephe (mentor)
MFC after: 2 weeks
Sponsored by: Microsoft
Differential Revision: https://reviews.freebsd.org/D8964
