Date: Tue, 2 Jul 2024 03:29:48 -0400
From: Adrián Moreno <amorenoz@...hat.com>
To: Aaron Conole <aconole@...hat.com>
Cc: netdev@...r.kernel.org, echaudro@...hat.com, horms@...nel.org, 
	i.maximets@....org, dev@...nvswitch.org, 
	Donald Hunter <donald.hunter@...il.com>, Jakub Kicinski <kuba@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, Pravin B Shelar <pshelar@....org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v7 05/10] net: openvswitch: add psample action

On Tue, Jul 02, 2024 at 03:05:02AM GMT, Adrián Moreno wrote:
> On Mon, Jul 01, 2024 at 02:23:12PM GMT, Aaron Conole wrote:
> > Adrian Moreno <amorenoz@...hat.com> 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 <echaudro@...hat.com>
> > > Signed-off-by: Adrian Moreno <amorenoz@...hat.com>
> > > ---
> >
> > 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.
> >
>
> We had a bit of discussion about this with Ilya. It seems "static
> inline" is a common pattern around the kernel. The coding style
> documentation says:
> "Generally, inline functions are preferable to macros resembling functions."
>
> So I think this "inline" is correct but I might be missing something.
>
> > > +#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.
>
> The uAPI header says:
>
> "
> 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.
> "
>
> Isn't this enough? What else would you add to make it even more clear?
>

BTW trunc also affects userspace and it's not explicitly documented.

> >
> > > +			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;
> >

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