Re: [PATCH] Work around dhclient brokenness (v2)

[Avi Kivity <avi@qumranet.com>]

Anthony Liguori wrote:
> With the latest GSO/csum offload patches, any guest using an unpatched version
> of dhclient (any Ubuntu guest, for instance), will no longer be able to get
> a DHCP address.
>
> dhclient is actually at fault here.  It uses AF_PACKET to receive DHCP responses
> but does not check auxdata to see if the packet has a valid csum.  This causes
> it to throw out the DHCP responses it gets from the virtio interface as there
> is not a valid checksum.
>
> Fedora has carried a patch to fix their dhclient (it's needed for Xen too) but
> this patch has not made it into a release of dhclient.  AFAIK, the patch is in
> the dhclient CVS but I cannot confirm since their CVS is not public.
>
> This patch, suggested by Rusty, looks for UDP packets (of a normal MTU) and
> explicitly adds a checksum to them if they are missing one.
>
> This allows unpatched dhclients to continue to work without needing to update
> the guest kernels.
>
> Since v1, we refined the search criteria to only consider packets originating
> from a DHCP server.  I also added a comment to note that we should disable this
> routine when we introduce zero copy.
>   

Applied, thanks.

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