Hi Florian, On Sun, May 26, 2013 at 10:48:26PM +0200, Florian Westphal wrote: > Hi. > > When using nfqueue, userspace currently has no way > to tell wheter queued packets have a bad checksum, i.e. > applications that need data integrity must do full checksum > validation in userspace (except maybe when only queueing in OUTPUT). > > However, there are several places where incoming packets are already > checksummed in kernel, before packet hits nfqueue, e.g. via nic rx > csum offload, or in conntrack. > > So I think it would be nice to provide a hint that kernel already did > checksumming. > > The SKB_INFO attribute added in -net for GRO support seems like a > candidate. However, since 'already checksummed' is the common case this > would mean adding that attribute most of the time. > > Unless we would do the opposite hint, i.e. tell userspace when > checksumming has NOT been performed yet. > > Such change would however need to go into -net, else userspace can't tell > 'checksum ok' from 'kernel too old to provide flag in SKB_INFO attribute'. User-space has no way to know what info flags are available. If we add more info flags in the future, we'll have the same problem that we have now. I mean, currently an unset info flag from userspace may mean: * It's actually unset. * It is not available in this kernel. So I think we need to pass a mask of available info flags, so user-space knows how to interpret what 'unset' means. The mask would also help to tell user-space that some info flag is not available. Regards. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
