linux-kernel - Re: [PATCHv4 net-next 09/10] openvswitch: Allow matching on conntrack label

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Message-ID: <CANr6G5xYJaEYsS9u9YZmz=mxEoknHiCp1FxWVtS69YCEbrfYSA@mail.gmail.com>
Date:	Thu, 20 Aug 2015 12:13:59 -0700
From:	Joe Stringer <joestringer@...ira.com>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, pablo <pablo@...filter.org>,
	Florian Westphal <fwestpha@...hat.com>,
	Hannes Sowa <hannes@...hat.com>, Thomas Graf <tgraf@...g.ch>,
	Justin Pettit <jpettit@...ira.com>,
	Jesse Gross <jesse@...ira.com>
Subject: Re: [PATCHv4 net-next 09/10] openvswitch: Allow matching on conntrack label

On 20 August 2015 at 08:45, Pravin Shelar <pshelar@...ira.com> wrote:
> On Wed, Aug 19, 2015 at 4:04 PM, Joe Stringer <joestringer@...ira.com> wrote:
>> Thanks for the review,
>>
>> On 19 August 2015 at 14:24, Pravin Shelar <pshelar@...ira.com> wrote:
>>> On Tue, Aug 18, 2015 at 4:39 PM, Joe Stringer <joestringer@...ira.com> wrote:
>>>> Allow matching and setting the conntrack label field. As with ct_mark,
>>>> this is populated by executing the CT action, and is a writable field.
>>>> Specifying a label and optional mask allows the label to be modified,
>>>> which takes effect on the entry found by the lookup of the CT action.
>>>>
>>>> E.g.: actions:ct(zone=1,label=1)
>>>>
>>>> This will perform conntrack lookup in zone 1, then modify the label for
>>>> that entry. The conntrack entry itself must be committed using the
>>>> "commit" flag in the conntrack action flags for this change to persist.
>>>>
>
>>
>>>>         return false;
>>>>  }
>>>> @@ -508,8 +601,12 @@ void ovs_ct_free_action(const struct nlattr *a)
>>>>
>>>>  void ovs_ct_init(struct net *net, struct ovs_ct_perdp_data *data)
>>>>  {
>>>> +       unsigned int n_bits = sizeof(struct ovs_key_ct_label) * BITS_PER_BYTE;
>>>> +
>>>>         data->xt_v4 = !nf_ct_l3proto_try_module_get(PF_INET);
>>>>         data->xt_v6 = !nf_ct_l3proto_try_module_get(PF_INET6);
>>>> +       if (nf_connlabels_get(net, n_bits);
>>>> +               OVS_NLERR(true, "Failed to set connlabel length");
>>>>  }
>>>>
>>> In case of error should we reject conntrack label actions? Otherwise
>>> user will never see any error. But action could drop packets.
>>
>> I suspect that currently errors would be seen from ovs_ct_set_label():
>>
>>>.......if (!cl || cl->words * sizeof(long) < OVS_CT_LABEL_LEN)
>>>.......>.......return -ENOSPC;
>>
>> So, for cmd_execute, userspace would see this. For regular handling,
>> pipeline processing would stop (so, drop).
>>
>> However, I agree it would be more friendly to have the attribute
>> rejected up-front. Just means we'll pass the datapath all the way
>> down:
>> ovs_nla_get_match()
>> --> ovs_key_from_nlattrs()
>> --> metadata_from_nlattrs()
>> --> ovs_ct_verify()

Incidentally, we generally don't have the datapath by this point
(ovs_nla_get_match()). There'd need to be a bit of rearranging in the
ovs_flow_cmd_* functions, which would include holding the locks for
longer. Given that the two most common cases are that either A) The
kernel is configured with connlabel support, and built with support
for at least 128 bits of label, or B) the kernel is configured without
connlabel, and this is handled already in ovs_ct_verify(), I don't
think it's worth making this particular change.
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