Re: [PATCHv5 net-next 10/10] openvswitch: Allow attaching helpers to ct action

On 25 August 2015 at 11:33, Thomas Graf [off-list ref] wrote:

On 08/24/15 at 05:32pm, Joe Stringer wrote:

quoted

Add support for using conntrack helpers to assist protocol detection.
The new OVS_CT_ATTR_HELPER attribute of the CT action specifies a helper
to be used for this connection. If no helper is specified, then helpers
will be automatically applied as per the sysctl configuration of
net.netfilter.nf_conntrack_helper.

The helper may be specified as part of the conntrack action, eg:
ct(helper=ftp). Initial packets for related connections should be
committed to allow later packets for the flow to be considered
established.

Example ovs-ofctl flows allowing FTP connections from ports 1->2:
in_port=1,tcp,action=ct(helper=ftp,commit),2
in_port=2,tcp,ct_state=-trk,action=ct(recirc)
in_port=2,tcp,ct_state=+trk-new+est,action=1
in_port=2,tcp,ct_state=+trk+rel,action=1

Not subject to this patch but we may want to revisit the syntax of the
state flags. It's neatly compressed like this but ct_state=untracked
ct_state=related might be more readable. The +trk should be implicit
for anything !untracked

Fair criticism. My thoughts were that this was a reasonable
middleground between representing masked flags like
"ct_state=0xc2/0xc3" vs. having overly verbose state descriptions like
the corresponding "ct_state=tracked,!new,established,reply_direction".
Either way, we need to represent the three possible states for each
flag: set and we care about the value, unset and we care about the
value, or we don't care about the value. Arguably the example above is
a bit imprecise, because the +trk flows intersect. Omitting the "+trk"
would make all of the return flows intersect.