[PATCH 0/5] High-speed tun receive and xmit

From: Rusty Russell
Date: Fri Apr 18 2008 - 00:35:25 EST


kvm (and lguest!) want to get more speed out of the tun device. We already
have an ABI for guest<->host comms, called virtio_ring; extending tun to
understand this (with its async nature and batching) make for an efficient
network.

But moreover: the same things that make virtio a good guest<->host transport
make it appealing as a userspace<->kernel transport. So rather than do
something just for tun, we create a /dev/vring. We could do a system call,
but /dev/vring is sufficient. It is a nice, simple format for normal tun
usage too.

We do need a small (backwards-compatible) extension to the ring format if
we're going to do this however, since we didn't previously expose the
consumer's view of the producer (and vice verse) in the ring because the
other end doesn't need to see it. However, it means that a middleman (as the
kvm or lguest launcher process now becomes) cannot save and restore all the
ring state.

Cheers,
Rusty.
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