On Tue, Aug 19, 2008 at 10:45:20AM +1000, Rusty Russell wrote:

> For those not following closely: We already have a method for the
> guest to accept or reject features.  Our problem is that the guest
> is already accepting the CSUM feature: but one critical userspace
> app (dhcp-client) can't actually handle it due to a bug.

Can't we just get dhcp-client client fixed upstream and let the
distro's update in a couple of months?

> The proposal is to add another mechanism, whereby the host doesn't
> advertise CSUM, but advertises a new CSUM2 feature.  The driver
> doesn't accept this by default: then guest userspace says "hey, I
> *really can* handle CSUM".  This would have to be done dby resetting
> the device in the ethtool callback (that's how we renegotiate
> features).  And guests need a special virtio hack in their init
> scripts.

If guest can have modified scripts for virtio and what not, they can
have a fixed dhcp-client.

> This leaves the small number of current users without CSUM (and
> hence GSO etc).  Yet they might not use dhcp with bridging anyway.

I think for now that's fine, it's a performance hit that people can
tweak away explicitly without having to add something like a CSUM2
feature.
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