port-xen/40650: xvif and modern linux

[jakllsch%kollasch.net@localhost]

>Number:         40650
>Category:       port-xen
>Synopsis:       xen xvif(4) network backend lacks support for 'copying'
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    port-xen-maintainer
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Sun Feb 15 17:50:00 +0000 2009
>Originator:     Jonathan A. Kollasch
>Release:        NetBSD 5.0_RC2
>Organization:
        
>Environment:
System: NetBSD terminus.kollasch.net 5.0_RC2 NetBSD 5.0_RC2 (XEN3_DOM0) #0: Thu 
Feb 12 00:18:10 UTC 2009 
build%kakrafoon.kollasch.net@localhost:/local/build/amd64-5-obj-20090211/sys/arch/amd64/compile/XEN3_DOM0
 amd64
Architecture: x86_64
Machine: amd64
>Description:
The NetBSD Xen paravirtual network backend driver doesn't support "copying",
which is required by modern mainstream vanilla Linux kernels.
>How-To-Repeat:
Try to run a Xen domU kernel from a modern linux distro, and note:

net eth0: backend does not support copying receive path

in it's dmesg.  I used one from Debian 5.0, but any paravirt_ops-based
Linux kernel should exibit this.
>Fix:
Implement 'copying' in the xen network backend, so that copying-only
frontends can work.