[ovs-dev] [RFC PATCH 2/5] netfilter: Factor out nf_ct_get_info().

Jarno Rajahalme jrajahalme at nicira.com
Wed Oct 21 21:38:35 UTC 2015

> On Oct 21, 2015, at 3:45 AM, Pablo Neira Ayuso <pablo at netfilter.org> wrote:
> On Tue, Oct 20, 2015 at 03:20:26PM -0700, Jarno Rajahalme wrote:
>> Define a new inline function to map conntrack status to enum
>> ip_conntrack_info.  This removes the need to otherwise duplicate this
>> code in a later patch.
> Where is that later patch that justifies this update?

It is in patch 5/5, ovs_ct_find_existing(). The intent it to locate an existing conntrack entry without modifying it, if such an entry exists. This is needed in a case where we first go through the conntrack (calling nf_conntrack_in), then recirculate (to match on the state bits), but do not find a matching flow entry in the flow table. In this case we issue an upcall and let the OVS userspace compute a new flow entry. When the packet gets back to kernel we have lost the skb (as we do not buffer it in the kernel after issuing the upcall). ovs_ct_find_existing() can then be used to populate the nfct and nfctinfo fields of the new skb, as if this skb had gone through the nf_conntrack_in() call. This allows us to pass the packet through NAT after such an upcall without passing the packet through nf_conntrack_in() twice.

ovs_ct_find_existing() is intended to be used only when we have evidence in the OVS flow key that the packet actually went through nf_conntrack_in() prior to the upcall. In the current version of the patches I do not have a test case for this, and I intend to separate out this change into a separate patch before the NAT patch for the next (non-RFC) version.

I could implement ovs_ct_find_existing() using exported conntrack APIs apart from this mapping from conntrack status to enum ip_conntrack_info. ovs_ct_find_existing() is in no way OVS specific, though, so it could be added to the conntrack proper as well, if so desired.


>> Signed-off-by: Jarno Rajahalme <jrajahalme at nicira.com>
>> ---
>> include/net/netfilter/nf_conntrack.h | 15 +++++++++++++++
>> net/netfilter/nf_conntrack_core.c    | 22 +++-------------------
>> 2 files changed, 18 insertions(+), 19 deletions(-)
>> diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
>> index fde4068..b3de10e 100644
>> --- a/include/net/netfilter/nf_conntrack.h
>> +++ b/include/net/netfilter/nf_conntrack.h
>> @@ -125,6 +125,21 @@ nf_ct_tuplehash_to_ctrack(const struct nf_conntrack_tuple_hash *hash)
>> 			    tuplehash[hash->tuple.dst.dir]);
>> }
>> +static inline enum ip_conntrack_info
>> +nf_ct_get_info(const struct nf_conntrack_tuple_hash *h)
>> +{
>> +	const struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(h);
>> +
>> +	/* Once we've had two way comms, always ESTABLISHED. */
>> +	if (test_bit(IPS_SEEN_REPLY_BIT, &ct->status))
>> +		return IP_CT_ESTABLISHED;
>> +	if (test_bit(IPS_EXPECTED_BIT, &ct->status))
>> +		return IP_CT_RELATED;
>> +	return IP_CT_NEW;
>> +}
> I would really like to see how you want to use this.

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