On Wed, May 29, 2013 at 01:25:42PM +0200, Florian Westphal wrote: > Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote: > > 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. > > Yes, I understand this. > > > 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. > > I plan to add a query feature that userspace can use to determine > supported attributes/flags. > > Userspace can then bind the queue and then figure out what > attributes are support. > > A more simple solution is to simply add a 32bit revision number > that is dumped to userspace. > > But regardless of the solution, its definitely -next material. > > I simply tried do get one-more-thing into -net. If you say no, > thats ok. I agree that the current situation is inconsistent. We have no way to know if the kernel validated the checksum or not from user-space, and I think this needs a fix. We can add a new NFQA_CFG_F_CSUM flag so user-space explicitly ask for assistance regarding checksumming from the kernel. If user-space tries to set that flag and the kernel does not support it, it will hit -EOPNOTSUPP. Thus, we can skip the feature retrieval thing. We would still need your patch as well. -- 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
