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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
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