Subject: Re: [PATCH net-next 6/8] net:openvswitch: add psample support

From: Aaron Conole <[email-masked]>
Date: Wed, 08 May 2024 11:25:23 -0400

Adrian Moreno <[email-masked]> writes:

> On 5/3/24 11:43 AM, Eelco Chaudron wrote:
>> On 24 Apr 2024, at 15:50, Adrian Moreno wrote:
>> 
>>> Add support for psample sampling via two new attributes to the
>>> OVS_ACTION_ATTR_SAMPLE action.
>>>
>>> OVS_SAMPLE_ATTR_PSAMPLE_GROUP used to pass an integer psample group_id.
>>> OVS_SAMPLE_ATTR_PSAMPLE_COOKIE used to pass a variable-length binary
>>> cookie that will be forwared to psample.
>>>
>>> The maximum length of the user-defined cookie is set to 16, same as
>>> tc_cookie, to discourage using cookies that will not be offloadable.
>>>
>>> In order to simplify the internal processing of the action and given the
>>> maximum size of the cookie is relatively small, add both fields to the
>>> internal-only struct sample_arg.
>>>
>>> The presence of a group_id mandates that the action shall called the
>>> psample module to multicast the packet with such group_id and the
>>> user-provided cookie if present. This behavior is orthonogal to
>>> also executing the nested actions if present.
>>>
>>> Signed-off-by: Adrian Moreno <[email-masked]>
>> This is not a full review yet. Just some comments, as I’m looking at
>> the user-space patch first and added similar comments.
>> I’ll do a proper review of this series once I’m done with user-space
>> part.
>> //Eelco
>> 
>>> ---
>>>   Documentation/netlink/specs/ovs_flow.yaml |  6 ++
>>>   include/uapi/linux/openvswitch.h          | 49 ++++++++++----
>>>   net/openvswitch/actions.c                 | 51 +++++++++++++--
>>>   net/openvswitch/flow_netlink.c            | 80 ++++++++++++++++++-----
>>>   4 files changed, 153 insertions(+), 33 deletions(-)
>>>
>>> diff --git a/Documentation/netlink/specs/ovs_flow.yaml b/Documentation/netlink/specs/ovs_flow.yaml
>>> index 4fdfc6b5cae9..5543c2937225 100644
>>> --- a/Documentation/netlink/specs/ovs_flow.yaml
>>> +++ b/Documentation/netlink/specs/ovs_flow.yaml
>>> @@ -825,6 +825,12 @@ attribute-sets:
>>>           name: actions
>>>           type: nest
>>>           nested-attributes: action-attrs
>>> +      -
>>> +        name: psample_group
>>> +        type: u32
>>> +      -
>>> +        name: psample_cookie
>>> +        type: binary
>>>     -
>>>       name: userspace-attrs
>>>       enum-name: ovs-userspace-attr
>>> diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
>>> index efc82c318fa2..e9cd6f3a952d 100644
>>> --- a/include/uapi/linux/openvswitch.h
>>> +++ b/include/uapi/linux/openvswitch.h
>>> @@ -639,6 +639,7 @@ enum ovs_flow_attr {
>>>   #define OVS_UFID_F_OMIT_MASK     (1 << 1)
>>>   #define OVS_UFID_F_OMIT_ACTIONS  (1 << 2)
>>>
>>> +#define OVS_PSAMPLE_COOKIE_MAX_SIZE 16
>>>   /**
>>>    * enum ovs_sample_attr - Attributes for %OVS_ACTION_ATTR_SAMPLE action.
>>>    * @OVS_SAMPLE_ATTR_PROBABILITY: 32-bit fraction of packets to sample with
>>> @@ -646,15 +647,27 @@ enum ovs_flow_attr {
>>>    * %UINT32_MAX samples all packets and intermediate values sample intermediate
>>>    * fractions of packets.
>>>    * @OVS_SAMPLE_ATTR_ACTIONS: Set of actions to execute in sampling event.
>>> - * Actions are passed as nested attributes.
>>> + * Actions are passed as nested attributes. Optional if
>>> + * OVS_SAMPLE_ATTR_PSAMPLE_GROUP is set.
>>> + * @OVS_SAMPLE_ATTR_PSAMPLE_GROUP: A 32-bit number to be used as psample group.
>>> + * Optional if OVS_SAMPLE_ATTR_ACTIONS is set.
>>> + * @OVS_SAMPLE_ATTR_PSAMPLE_COOKIE: A variable-length binary cookie that, if
>>> + * provided, will be copied to the psample cookie.
>> As there is a limit of to the cookie should we mention it here?
>> 
>
> I thought OVS_PSAMPLE_COOKIE_MAX_SIZE was expressive enough but sure,
> we can also mention it here.
>
>>>    *
>>> - * Executes the specified actions with the given probability on a per-packet
>>> - * basis.
>>> + * Either OVS_SAMPLE_ATTR_PSAMPLE_GROUP or OVS_SAMPLE_ATTR_ACTIONS must be
>>> + * specified.
>>> + *
>>> + * Executes the specified actions and/or sends the packet to psample
>>> + * with the given probability on a per-packet basis.
>>>    */
>>>   enum ovs_sample_attr {
>>>   	OVS_SAMPLE_ATTR_UNSPEC,
>>> -	OVS_SAMPLE_ATTR_PROBABILITY, /* u32 number */
>>> -	OVS_SAMPLE_ATTR_ACTIONS,     /* Nested OVS_ACTION_ATTR_* attributes. */
>>> +	OVS_SAMPLE_ATTR_PROBABILITY,	/* u32 number */
>>> +	OVS_SAMPLE_ATTR_ACTIONS,	/* Nested OVS_ACTION_ATTR_
>> Missing * after OVS_ACTION_ATTR_
>
> As a matter of fact, adding an * makes checkpatch generate a warning
> IIRC. That's why I initially removed it. I can look at fixing
> checkpatch instead.

I think we can ignore the warning.  Alternatively, consider not changing
the comment spacing for the existing comments.

>> 
>>> +					 * attributes.
>>> +					 */
>>> +	OVS_SAMPLE_ATTR_PSAMPLE_GROUP,	/* u32 number */
>>> +	OVS_SAMPLE_ATTR_PSAMPLE_COOKIE,	/* binary */
>> As these are general sample options, I would not add the PSAMPLE
>> reference. Other data paths could use a different implementation. So
>> I guess OVS_SAMPLE_ATTR_GROUP_ID and OVS_SAMPLE_ATTR_COOKIE would be
>> enough.
>> 
>
> OK. But isn't the API already psample-ish? I mean that the group_id is
> something specific to psample that might not be present in other
> datapath implementation.
>
>
>>>   	__OVS_SAMPLE_ATTR_MAX,
>>>
>>>   #ifdef __KERNEL__
>>> @@ -665,13 +678,27 @@ enum ovs_sample_attr {
>>>   #define OVS_SAMPLE_ATTR_MAX (__OVS_SAMPLE_ATTR_MAX - 1)
>>>
>>>   #ifdef __KERNEL__
>>> +
>>> +/* Definition for flags in struct sample_arg. */
>>> +enum {
>>> +	/* When set, actions in sample will not change the flows. */
>>> +	OVS_SAMPLE_ARG_FLAG_EXEC = 1 << 0,
>>> +	/* When set, the packet will be sent to psample. */
>>> +	OVS_SAMPLE_ARG_FLAG_PSAMPLE = 1 << 1,
>>> +};
>>> +
>>>   struct sample_arg {
>>> -	bool exec;                   /* When true, actions in sample will not
>>> -				      * change flow keys. False otherwise.
>>> -				      */
>>> -	u32  probability;            /* Same value as
>>> -				      * 'OVS_SAMPLE_ATTR_PROBABILITY'.
>>> -				      */
>> Not sure if you can actually do this, you are changing a structure
>> that is part of the UAPI. This change breaks backwards
>> compatibility.
>> 
>
> Hmmm... this the internal argument structure protected by #ifdef
> __KERNEL__. It is used in several actions to optimize the internal
> action handling (i.e: using a compact struct instead of a list of
> netlink attributes). I guess the reason for having it in this file is
> because the attribute enum is being reused, but I wouldn't think of
> this struct as part of the uAPI.
>
> If the (#ifdef __KERNEL__) does not exclude this struct from the uAPI
> I think we should move it (all of them actually) to some internal
> file.
>
>> 
>>> +	u16 flags;		/* Flags that modify the behavior of the
>>> +				 * action. See SAMPLE_ARG_FLAG_*.
>>> +				 */
>>> +	u32  probability;       /* Same value as
>>> +				 * 'OVS_SAMPLE_ATTR_PROBABILITY'.
>>> +				 */
>>> +	u32  group_id;		/* Same value as
>>> +				 * 'OVS_SAMPLE_ATTR_PSAMPLE_GROUP'.
>>> +				 */
>>> +	u8  cookie_len;		/* Length of psample cookie. */
>>> +	char cookie[OVS_PSAMPLE_COOKIE_MAX_SIZE]; /* psample cookie data. */
>> Would it make sense for the cookie also to be u8?
>> 
>
> Yes, probably.
>
>>>   };
>>>   #endif
>>>
>>> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
>>> index 6fcd7e2ca81f..eb3166986fd2 100644
>>> --- a/net/openvswitch/actions.c
>>> +++ b/net/openvswitch/actions.c
>>> @@ -24,6 +24,7 @@
>>>   #include <net/checksum.h>
>>>   #include <net/dsfield.h>
>>>   #include <net/mpls.h>
>>> +#include <net/psample.h>
>>>   #include <net/sctp/checksum.h>
>>>
>>>   #include "datapath.h"
>>> @@ -1025,6 +1026,34 @@ static int dec_ttl_exception_handler(struct datapath *dp, struct sk_buff *skb,
>>>   	return 0;
>>>   }
>>>
>>> +static int ovs_psample_packet(struct datapath *dp, struct sw_flow_key *key,
>>> +			      const struct sample_arg *arg,
>>> +			      struct sk_buff *skb)
>>> +{
>>> +	struct psample_group psample_group = {};
>>> +	struct psample_metadata md = {};
>>> +	struct vport *input_vport;
>>> +	u32 rate;
>>> +
>>> +	psample_group.group_num = arg->group_id;
>>> +	psample_group.net = ovs_dp_get_net(dp);
>>> +
>>> +	input_vport = ovs_vport_rcu(dp, key->phy.in_port);
>>> +	if (!input_vport)
>>> +		input_vport = ovs_vport_rcu(dp, OVSP_LOCAL);
>>> +
>>> +	md.in_ifindex = input_vport->dev->ifindex;
>>> +	md.user_cookie = arg->cookie_len ? &arg->cookie[0] : NULL;
>>> +	md.user_cookie_len = arg->cookie_len;
>>> +	md.trunc_size = skb->len;
>>> +
>>> +	rate = arg->probability ? U32_MAX / arg->probability : 0;
>>> +
>>> +	psample_sample_packet(&psample_group, skb, rate, &md);
>> Does this mean now the ovs module, now is dependent on the presence
>> of psample? I think we should only support sampling to psample if
>> the module exists, else we should return an error. There might be
>> distributions not including psample by default.
>
> Agree. I'll add some compile-time checks the same way we do with nf_nat.
>
>> 
>>> +
>>> +	return 0;
>>> +}
>>> +
>>>   /* When 'last' is true, sample() should always consume the 'skb'.
>>>    * Otherwise, sample() should keep 'skb' intact regardless what
>>>    * actions are executed within sample().
>>> @@ -1033,11 +1062,12 @@ static int sample(struct datapath *dp, struct sk_buff *skb,
>>>   		  struct sw_flow_key *key, const struct nlattr *attr,
>>>   		  bool last)
>>>   {
>>> -	struct nlattr *actions;
>>> +	const struct sample_arg *arg;
>>>   	struct nlattr *sample_arg;
>>>   	int rem = nla_len(attr);
>>> -	const struct sample_arg *arg;
>>> +	struct nlattr *actions;
>>>   	bool clone_flow_key;
>>> +	int ret;
>>>
>>>   	/* The first action is always 'OVS_SAMPLE_ATTR_ARG'. */
>>>   	sample_arg = nla_data(attr);
>>> @@ -1051,9 +1081,20 @@ static int sample(struct datapath *dp, struct sk_buff *skb,
>>>   		return 0;
>>>   	}
>>>
>>> -	clone_flow_key = !arg->exec;
>>> -	return clone_execute(dp, skb, key, 0, actions, rem, last,
>>> -			     clone_flow_key);
>>> +	if (arg->flags & OVS_SAMPLE_ARG_FLAG_PSAMPLE) {
>>> +		ret = ovs_psample_packet(dp, key, arg, skb);
>>> +		if (ret)
>>> +			return ret;
>>> +	}
>>> +
>>> +	if (nla_ok(actions, rem)) {
>>> +		clone_flow_key = !(arg->flags & OVS_SAMPLE_ARG_FLAG_EXEC);
>>> +		ret = clone_execute(dp, skb, key, 0, actions, rem, last,
>>> +				    clone_flow_key);
>>> +	} else if (last) {
>>> +		ovs_kfree_skb_reason(skb, OVS_DROP_LAST_ACTION);
>>> +	}
>>> +	return ret;
>>>   }
>>>
>>>   /* When 'last' is true, clone() should always consume the 'skb'.
>>> diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
>>> index f224d9bcea5e..1a348d3905fc 100644
>>> --- a/net/openvswitch/flow_netlink.c
>>> +++ b/net/openvswitch/flow_netlink.c
>>> @@ -2561,6 +2561,9 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
>>>   				  u32 mpls_label_count, bool log,
>>>   				  u32 depth);
>>>
>>> +static int copy_action(const struct nlattr *from,
>>> +		       struct sw_flow_actions **sfa, bool log);
>>> +
>>>   static int validate_and_copy_sample(struct net *net, const struct nlattr *attr,
>>>   				    const struct sw_flow_key *key,
>>>   				    struct sw_flow_actions **sfa,
>>> @@ -2569,10 +2572,10 @@ static int validate_and_copy_sample(struct net *net, const struct nlattr *attr,
>>>   				    u32 depth)
>>>   {
>>>   	const struct nlattr *attrs[OVS_SAMPLE_ATTR_MAX + 1];
>>> -	const struct nlattr *probability, *actions;
>>> +	const struct nlattr *probability, *actions, *group, *cookie;
>>> +	struct sample_arg arg = {};
>>>   	const struct nlattr *a;
>>>   	int rem, start, err;
>>> -	struct sample_arg arg;
>>>
>>>   	memset(attrs, 0, sizeof(attrs));
>>>   	nla_for_each_nested(a, attr, rem) {
>>> @@ -2589,7 +2592,19 @@ static int validate_and_copy_sample(struct net *net, const struct nlattr *attr,
>>>   		return -EINVAL;
>>>
>>>   	actions = attrs[OVS_SAMPLE_ATTR_ACTIONS];
>>> -	if (!actions || (nla_len(actions) && nla_len(actions) < NLA_HDRLEN))
>>> +	if (actions && (!nla_len(actions) || nla_len(actions) < NLA_HDRLEN))
>>> +		return -EINVAL;
>>> +
>>> +	group = attrs[OVS_SAMPLE_ATTR_PSAMPLE_GROUP];
>>> +	if (group && nla_len(group) != sizeof(u32))
>>> +		return -EINVAL;
>>> +
>>> +	cookie = attrs[OVS_SAMPLE_ATTR_PSAMPLE_COOKIE];
>>> +	if (cookie &&
>>> +	    (!group || nla_len(cookie) > OVS_PSAMPLE_COOKIE_MAX_SIZE))
>>> +		return -EINVAL;
>>> +
>>> +	if (!group && !actions)
>>>   		return -EINVAL;
>>>
>>>   	/* validation done, copy sample action. */
>>> @@ -2608,7 +2623,19 @@ static int validate_and_copy_sample(struct net *net, const struct nlattr *attr,
>>>   	 * If the sample is the last action, it can always be excuted
>>>   	 * rather than deferred.
>>>   	 */
>>> -	arg.exec = last || !actions_may_change_flow(actions);
>>> +	if (actions && (last || !actions_may_change_flow(actions)))
>>> +		arg.flags |= OVS_SAMPLE_ARG_FLAG_EXEC;
>>> +
>>> +	if (group) {
>>> +		arg.flags |= OVS_SAMPLE_ARG_FLAG_PSAMPLE;
>>> +		arg.group_id = nla_get_u32(group);
>>> +	}
>>> +
>>> +	if (cookie) {
>>> +		memcpy(&arg.cookie[0], nla_data(cookie), nla_len(cookie));
>>> +		arg.cookie_len = nla_len(cookie);
>>> +	}
>>> +
>>>   	arg.probability = nla_get_u32(probability);
>>>
>>>   	err = ovs_nla_add_action(sfa, OVS_SAMPLE_ATTR_ARG, &arg, sizeof(arg),
>>> @@ -2616,12 +2643,13 @@ static int validate_and_copy_sample(struct net *net, const struct nlattr *attr,
>>>   	if (err)
>>>   		return err;
>>>
>>> -	err = __ovs_nla_copy_actions(net, actions, key, sfa,
>>> -				     eth_type, vlan_tci, mpls_label_count, log,
>>> -				     depth + 1);
>>> -
>>> -	if (err)
>>> -		return err;
>>> +	if (actions) {
>>> +		err = __ovs_nla_copy_actions(net, actions, key, sfa,
>>> +					     eth_type, vlan_tci,
>>> +					     mpls_label_count, log, depth + 1);
>>> +		if (err)
>>> +			return err;
>>> +	}
>>>
>>>   	add_nested_action_end(*sfa, start);
>>>
>>> @@ -3553,20 +3581,38 @@ static int sample_action_to_attr(const struct nlattr *attr,
>>>   		goto out;
>>>   	}
>>>
>>> -	ac_start = nla_nest_start_noflag(skb, OVS_SAMPLE_ATTR_ACTIONS);
>>> -	if (!ac_start) {
>>> -		err = -EMSGSIZE;
>>> -		goto out;
>>> +	if (arg->flags & OVS_SAMPLE_ARG_FLAG_PSAMPLE) {
>>> +		if (nla_put_u32(skb, OVS_SAMPLE_ATTR_PSAMPLE_GROUP,
>>> +				arg->group_id)) {
>>> +			err = -EMSGSIZE;
>>> +			goto out;
>>> +		}
>>> +
>>> +		if (arg->cookie_len &&
>>> +		    nla_put(skb, OVS_SAMPLE_ATTR_PSAMPLE_COOKIE,
>>> +			    arg->cookie_len, &arg->cookie[0])) {
>>> +			err = -EMSGSIZE;
>>> +			goto out;
>>> +		}
>>>   	}
>>>
>>> -	err = ovs_nla_put_actions(actions, rem, skb);
>>> +	if (nla_ok(actions, rem)) {
>>> +		ac_start = nla_nest_start_noflag(skb, OVS_SAMPLE_ATTR_ACTIONS);
>>> +		if (!ac_start) {
>>> +			err = -EMSGSIZE;
>>> +			goto out;
>>> +		}
>>> +		err = ovs_nla_put_actions(actions, rem, skb);
>>> +	}
>>>
>>>   out:
>>>   	if (err) {
>>> -		nla_nest_cancel(skb, ac_start);
>>> +		if (ac_start)
>>> +			nla_nest_cancel(skb, ac_start);
>>>   		nla_nest_cancel(skb, start);
>>>   	} else {
>>> -		nla_nest_end(skb, ac_start);
>>> +		if (ac_start)
>>> +			nla_nest_end(skb, ac_start);
>>>   		nla_nest_end(skb, start);
>>>   	}
>>>
>>> -- 2.44.0
>>