Re: [PATCH v2] network: add rule to nftables backend that zeroes checksum of DHCP responses
On Tue, Oct 29, 2024 at 01:09:00PM +0000, Andrea Bolognani wrote:
On Tue, Oct 29, 2024 at 12:46:55PM +0000, Daniel P. Berrangé wrote:
> A key difference that is probably relevant is that netbsd is
> using an e1000 NIC in QEMU, while openbsd is using a virtio-net
> NIC. At least when created by virt-manager.
>
> AFAIR, QEMU's magic checksum offload only happens for virtio-net,
> so presumably our rules are incompatible with non-virtio-net NICs
> in someway.
Yes, that's it! The GNU/Hurd and Haiku guests are also using e1000,
since virtio drivers are not available there; moreover, if I switch a
random Linux guest from virtio-net to e1000 I can reproduce the issue
there as well.
Incidentally, I think this has crossed the threshold where the cure is
worse than the disease.
We cannot ship the forthcoming libvirt release with a checksum "fix"
that breaks all usage of NICs that aren't virtio-net, as that guarantees
brokeness for all historical OS.
If we can't quickly find a way to improve this, I think we need to
revert (or disable) the checksum zero'ing fix for this release and
spend more time investigating it.
With regards,
Daniel
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