Subject: Re: [PATCH net-next v7 05/10] net: openvswitch: add psample action

From: Aaron Conole <[email-masked]>
Date: Mon, 01 Jul 2024 14:23:12 -0400

Adrian Moreno <[email-masked]> writes:

> Add support for a new action: psample.
>
> This action accepts a u32 group id and a variable-length cookie and uses
> the psample multicast group to make the packet available for
> observability.
>
> 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.
>
> Acked-by: Eelco Chaudron <[email-masked]>
> Signed-off-by: Adrian Moreno <[email-masked]>
> ---

Hi Adrian,

Just some nits below.

>  Documentation/netlink/specs/ovs_flow.yaml | 17 ++++++++
>  include/uapi/linux/openvswitch.h          | 28 ++++++++++++++
>  net/openvswitch/Kconfig                   |  1 +
>  net/openvswitch/actions.c                 | 47 +++++++++++++++++++++++
>  net/openvswitch/flow_netlink.c            | 32 ++++++++++++++-
>  5 files changed, 124 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/netlink/specs/ovs_flow.yaml b/Documentation/netlink/specs/ovs_flow.yaml
> index 4fdfc6b5cae9..46f5d1cd8a5f 100644
> --- a/Documentation/netlink/specs/ovs_flow.yaml
> +++ b/Documentation/netlink/specs/ovs_flow.yaml
> @@ -727,6 +727,12 @@ attribute-sets:
>          name: dec-ttl
>          type: nest
>          nested-attributes: dec-ttl-attrs
> +      -
> +        name: psample
> +        type: nest
> +        nested-attributes: psample-attrs
> +        doc: |
> +          Sends a packet sample to psample for external observation.
>    -
>      name: tunnel-key-attrs
>      enum-name: ovs-tunnel-key-attr
> @@ -938,6 +944,17 @@ attribute-sets:
>        -
>          name: gbp
>          type: u32
> +  -
> +    name: psample-attrs
> +    enum-name: ovs-psample-attr
> +    name-prefix: ovs-psample-attr-
> +    attributes:
> +      -
> +        name: group
> +        type: u32
> +      -
> +        name: cookie
> +        type: binary
>  
>  operations:
>    name-prefix: ovs-flow-cmd-
> diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
> index efc82c318fa2..3dd653748725 100644
> --- a/include/uapi/linux/openvswitch.h
> +++ b/include/uapi/linux/openvswitch.h
> @@ -914,6 +914,31 @@ struct check_pkt_len_arg {
>  };
>  #endif
>  
> +#define OVS_PSAMPLE_COOKIE_MAX_SIZE 16
> +/**
> + * enum ovs_psample_attr - Attributes for %OVS_ACTION_ATTR_PSAMPLE
> + * action.
> + *
> + * @OVS_PSAMPLE_ATTR_GROUP: 32-bit number to identify the source of the
> + * sample.
> + * @OVS_PSAMPLE_ATTR_COOKIE: An optional variable-length binary cookie that
> + * contains user-defined metadata. The maximum length is
> + * OVS_PSAMPLE_COOKIE_MAX_SIZE bytes.
> + *
> + * Sends the packet to the psample multicast group with the specified group and
> + * cookie. It is possible to combine this action with the
> + * %OVS_ACTION_ATTR_TRUNC action to limit the size of the sample.
> + */
> +enum ovs_psample_attr {
> +	OVS_PSAMPLE_ATTR_GROUP = 1,	/* u32 number. */
> +	OVS_PSAMPLE_ATTR_COOKIE,	/* Optional, user specified cookie. */
> +
> +	/* private: */
> +	__OVS_PSAMPLE_ATTR_MAX
> +};
> +
> +#define OVS_PSAMPLE_ATTR_MAX (__OVS_PSAMPLE_ATTR_MAX - 1)
> +
>  /**
>   * enum ovs_action_attr - Action types.
>   *
> @@ -966,6 +991,8 @@ struct check_pkt_len_arg {
>   * of l3 tunnel flag in the tun_flags field of OVS_ACTION_ATTR_ADD_MPLS
>   * argument.
>   * @OVS_ACTION_ATTR_DROP: Explicit drop action.
> + * @OVS_ACTION_ATTR_PSAMPLE: Send a sample of the packet to external observers
> + * via psample.
>   *
>   * Only a single header can be set with a single %OVS_ACTION_ATTR_SET.  Not all
>   * fields within a header are modifiable, e.g. the IPv4 protocol and fragment
> @@ -1004,6 +1031,7 @@ enum ovs_action_attr {
>  	OVS_ACTION_ATTR_ADD_MPLS,     /* struct ovs_action_add_mpls. */
>  	OVS_ACTION_ATTR_DEC_TTL,      /* Nested OVS_DEC_TTL_ATTR_*. */
>  	OVS_ACTION_ATTR_DROP,         /* u32 error code. */
> +	OVS_ACTION_ATTR_PSAMPLE,      /* Nested OVS_PSAMPLE_ATTR_*. */
>  
>  	__OVS_ACTION_ATTR_MAX,	      /* Nothing past this will be accepted
>  				       * from userspace. */
> diff --git a/net/openvswitch/Kconfig b/net/openvswitch/Kconfig
> index 29a7081858cd..2535f3f9f462 100644
> --- a/net/openvswitch/Kconfig
> +++ b/net/openvswitch/Kconfig
> @@ -10,6 +10,7 @@ config OPENVSWITCH
>  		   (NF_CONNTRACK && ((!NF_DEFRAG_IPV6 || NF_DEFRAG_IPV6) && \
>  				     (!NF_NAT || NF_NAT) && \
>  				     (!NETFILTER_CONNCOUNT || NETFILTER_CONNCOUNT)))
> +	depends on PSAMPLE || !PSAMPLE
>  	select LIBCRC32C
>  	select MPLS
>  	select NET_MPLS_GSO
> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> index 964225580824..a035b7e677dd 100644
> --- a/net/openvswitch/actions.c
> +++ b/net/openvswitch/actions.c
> @@ -24,6 +24,11 @@
>  #include <net/checksum.h>
>  #include <net/dsfield.h>
>  #include <net/mpls.h>
> +
> +#if IS_ENABLED(CONFIG_PSAMPLE)
> +#include <net/psample.h>
> +#endif
> +
>  #include <net/sctp/checksum.h>
>  
>  #include "datapath.h"
> @@ -1299,6 +1304,39 @@ static int execute_dec_ttl(struct sk_buff *skb, struct sw_flow_key *key)
>  	return 0;
>  }
>  
> +#if IS_ENABLED(CONFIG_PSAMPLE)
> +static void execute_psample(struct datapath *dp, struct sk_buff *skb,
> +			    const struct nlattr *attr)
> +{
> +	struct psample_group psample_group = {};
> +	struct psample_metadata md = {};
> +	const struct nlattr *a;
> +	int rem;
> +
> +	nla_for_each_attr(a, nla_data(attr), nla_len(attr), rem) {
> +		switch (nla_type(a)) {
> +		case OVS_PSAMPLE_ATTR_GROUP:
> +			psample_group.group_num = nla_get_u32(a);
> +			break;
> +
> +		case OVS_PSAMPLE_ATTR_COOKIE:
> +			md.user_cookie = nla_data(a);
> +			md.user_cookie_len = nla_len(a);
> +			break;
> +		}
> +	}
> +
> +	psample_group.net = ovs_dp_get_net(dp);
> +	md.in_ifindex = OVS_CB(skb)->input_vport->dev->ifindex;
> +	md.trunc_size = skb->len - OVS_CB(skb)->cutlen;
> +
> +	psample_sample_packet(&psample_group, skb, 0, &md);
> +}
> +#else
> +static inline void execute_psample(struct datapath *dp, struct sk_buff *skb,
> +				   const struct nlattr *attr) {}

I noticed that this got flagged in patchwork since it is 'static inline'
while being part of a complete translation unit - but I also see some
other places where that has been done.  I guess it should be just
'static' though.  I don't feel very strongly about it.

> +#endif
> +
>  /* Execute a list of actions against 'skb'. */
>  static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
>  			      struct sw_flow_key *key,
> @@ -1502,6 +1540,15 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
>  			ovs_kfree_skb_reason(skb, reason);
>  			return 0;
>  		}
> +
> +		case OVS_ACTION_ATTR_PSAMPLE:
> +			execute_psample(dp, skb, a);
> +			OVS_CB(skb)->cutlen = 0;

We may want to document that trunc is also impacted by psample calls.
Right now, it is only mentioned for a single OUTPUT action.
Alternatively, we could either ignore trunc, or not reset here.

> +			if (nla_is_last(a, rem)) {
> +				consume_skb(skb);
> +				return 0;
> +			}
> +			break;
>  		}
>  
>  		if (unlikely(err)) {
> diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
> index f224d9bcea5e..c92bdc4dfe19 100644
> --- a/net/openvswitch/flow_netlink.c
> +++ b/net/openvswitch/flow_netlink.c
> @@ -64,6 +64,7 @@ static bool actions_may_change_flow(const struct nlattr *actions)
>  		case OVS_ACTION_ATTR_TRUNC:
>  		case OVS_ACTION_ATTR_USERSPACE:
>  		case OVS_ACTION_ATTR_DROP:
> +		case OVS_ACTION_ATTR_PSAMPLE:
>  			break;
>  
>  		case OVS_ACTION_ATTR_CT:
> @@ -2409,7 +2410,7 @@ static void ovs_nla_free_nested_actions(const struct nlattr *actions, int len)
>  	/* Whenever new actions are added, the need to update this
>  	 * function should be considered.
>  	 */
> -	BUILD_BUG_ON(OVS_ACTION_ATTR_MAX != 24);
> +	BUILD_BUG_ON(OVS_ACTION_ATTR_MAX != 25);
>  
>  	if (!actions)
>  		return;
> @@ -3157,6 +3158,28 @@ static int validate_and_copy_check_pkt_len(struct net *net,
>  	return 0;
>  }
>  
> +static int validate_psample(const struct nlattr *attr)
> +{
> +	static const struct nla_policy policy[OVS_PSAMPLE_ATTR_MAX + 1] = {
> +		[OVS_PSAMPLE_ATTR_GROUP] = { .type = NLA_U32 },
> +		[OVS_PSAMPLE_ATTR_COOKIE] = {
> +			.type = NLA_BINARY,
> +			.len = OVS_PSAMPLE_COOKIE_MAX_SIZE,
> +		},
> +	};
> +	struct nlattr *a[OVS_PSAMPLE_ATTR_MAX + 1];
> +	int err;
> +
> +	if (!IS_ENABLED(CONFIG_PSAMPLE))
> +		return -EOPNOTSUPP;
> +
> +	err = nla_parse_nested(a, OVS_PSAMPLE_ATTR_MAX, attr, policy, NULL);
> +	if (err)
> +		return err;
> +
> +	return a[OVS_PSAMPLE_ATTR_GROUP] ? 0 : -EINVAL;
> +}
> +
>  static int copy_action(const struct nlattr *from,
>  		       struct sw_flow_actions **sfa, bool log)
>  {
> @@ -3212,6 +3235,7 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
>  			[OVS_ACTION_ATTR_ADD_MPLS] = sizeof(struct ovs_action_add_mpls),
>  			[OVS_ACTION_ATTR_DEC_TTL] = (u32)-1,
>  			[OVS_ACTION_ATTR_DROP] = sizeof(u32),
> +			[OVS_ACTION_ATTR_PSAMPLE] = (u32)-1,
>  		};
>  		const struct ovs_action_push_vlan *vlan;
>  		int type = nla_type(a);
> @@ -3490,6 +3514,12 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
>  				return -EINVAL;
>  			break;
>  
> +		case OVS_ACTION_ATTR_PSAMPLE:
> +			err = validate_psample(a);
> +			if (err)
> +				return err;
> +			break;
> +
>  		default:
>  			OVS_NLERR(log, "Unknown Action type %d", type);
>  			return -EINVAL;