Date: Tue, 11 Jun 2024 15:42:48 +0000
From: Adrián Moreno <amorenoz@...hat.com>
To: Aaron Conole <aconole@...hat.com>
Cc: netdev@...r.kernel.org, dev@...nvswitch.org, 
	Paolo Abeni <pabeni@...hat.com>, Donald Hunter <donald.hunter@...il.com>, 
	linux-kernel@...r.kernel.org, i.maximets@....org, 
	Eric Dumazet <edumazet@...gle.com>, horms@...nel.org, Jakub Kicinski <kuba@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [ovs-dev] [PATCH net-next v2 5/9] net: openvswitch: add
 emit_sample action

On Tue, Jun 11, 2024 at 09:54:49AM GMT, Aaron Conole wrote:
> Adrián Moreno <amorenoz@...hat.com> writes:
>
> > On Mon, Jun 10, 2024 at 11:46:14AM GMT, Aaron Conole wrote:
> >> Adrian Moreno <amorenoz@...hat.com> writes:
> >>
> >> > Add support for a new action: emit_sample.
> >> >
> >> > 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.
> >> >
> >> > Signed-off-by: Adrian Moreno <amorenoz@...hat.com>
> >> > ---
> >>
> >> I saw some of the nits Simon raised - I'll add one more below.
> >>
> >> I haven't gone through the series thoroughly enough to make a detailed
> >> review.
> >>
> >> >  Documentation/netlink/specs/ovs_flow.yaml | 17 ++++++++
> >> >  include/uapi/linux/openvswitch.h          | 25 ++++++++++++
> >> >  net/openvswitch/actions.c                 | 50 +++++++++++++++++++++++
> >> >  net/openvswitch/flow_netlink.c            | 33 ++++++++++++++-
> >> >  4 files changed, 124 insertions(+), 1 deletion(-)
> >> >
> >> > diff --git a/Documentation/netlink/specs/ovs_flow.yaml b/Documentation/netlink/specs/ovs_flow.yaml
> >> > index 4fdfc6b5cae9..a7ab5593a24f 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: emit-sample
> >> > +        type: nest
> >> > +        nested-attributes: emit-sample-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: emit-sample-attrs
> >> > +    enum-name: ovs-emit-sample-attr
> >> > +    name-prefix: ovs-emit-sample-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..a0e9dde0584a 100644
> >> > --- a/include/uapi/linux/openvswitch.h
> >> > +++ b/include/uapi/linux/openvswitch.h
> >> > @@ -914,6 +914,30 @@ struct check_pkt_len_arg {
> >> >  };
> >> >  #endif
> >> >
> >> > +#define OVS_EMIT_SAMPLE_COOKIE_MAX_SIZE 16
> >> > +/**
> >> > + * enum ovs_emit_sample_attr - Attributes for %OVS_ACTION_ATTR_EMIT_SAMPLE
> >> > + * action.
> >> > + *
> >> > + * @OVS_EMIT_SAMPLE_ATTR_GROUP: 32-bit number to identify the source of the
> >> > + * sample.
> >> > + * @OVS_EMIT_SAMPLE_ATTR_COOKIE: A variable-length binary cookie that contains
> >> > + * user-defined metadata. The maximum length is 16 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 packet being emitted.
> >> > + */
> >> > +enum ovs_emit_sample_attr {
> >> > +	OVS_EMIT_SAMPLE_ATTR_UNPSEC,
> >> > +	OVS_EMIT_SAMPLE_ATTR_GROUP,	/* u32 number. */
> >> > +	OVS_EMIT_SAMPLE_ATTR_COOKIE,	/* Optional, user specified cookie. */
> >> > +	__OVS_EMIT_SAMPLE_ATTR_MAX
> >> > +};
> >> > +
> >> > +#define OVS_EMIT_SAMPLE_ATTR_MAX (__OVS_EMIT_SAMPLE_ATTR_MAX - 1)
> >> > +
> >> > +
> >> >  /**
> >> >   * enum ovs_action_attr - Action types.
> >> >   *
> >> > @@ -1004,6 +1028,7 @@ 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_EMIT_SAMPLE,  /* Nested OVS_EMIT_SAMPLE_ATTR_*. */
> >> >
> >> >  	__OVS_ACTION_ATTR_MAX,	      /* Nothing past this will be accepted
> >> >  				       * from userspace. */
> >> > diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> >> > index 964225580824..3b4dba0ded59 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 +1304,46 @@ static int execute_dec_ttl(struct sk_buff *skb, struct sw_flow_key *key)
> >> >  	return 0;
> >> >  }
> >> >
> >> > +static int execute_emit_sample(struct datapath *dp, struct sk_buff *skb,
> >> > +			       const struct sw_flow_key *key,
> >> > +			       const struct nlattr *attr)
> >> > +{
> >> > +#if IS_ENABLED(CONFIG_PSAMPLE)
> >> > +	struct psample_group psample_group = {};
> >> > +	struct psample_metadata md = {};
> >> > +	struct vport *input_vport;
> >> > +	const struct nlattr *a;
> >> > +	int rem;
> >> > +
> >> > +	for (a = nla_data(attr), rem = nla_len(attr); rem > 0;
> >> > +	     a = nla_next(a, &rem)) {
> >> > +		switch (nla_type(a)) {
> >> > +		case OVS_EMIT_SAMPLE_ATTR_GROUP:
> >> > +			psample_group.group_num = nla_get_u32(a);
> >> > +			break;
> >> > +
> >> > +		case OVS_EMIT_SAMPLE_ATTR_COOKIE:
> >> > +			md.user_cookie = nla_data(a);
> >> > +			md.user_cookie_len = nla_len(a);
> >> > +			break;
> >> > +		}
> >> > +	}
> >> > +
> >> > +	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.trunc_size = skb->len - OVS_CB(skb)->cutlen;
> >> > +
> >> > +	psample_sample_packet(&psample_group, skb, 0, &md);
> >> > +#endif
> >> > +
> >> > +	return 0;
> >>
> >> Why this return here?  Doesn't seem used anywhere else.
> >>
> >
> > It is being used in "do_execute_actions", right?
> > All non-skb-consuming actions set the value of "err" and break from the
> > switch-case so that the the packet is dropped with OVS_DROP_ACTION_ERROR reason.
> >
> > Am i missing something?
>
> I think so.  For example, it isn't used when the function cannot
> possibly error.
>
> see the following cases:
>
> OVS_ACTION_ATTR_HASH
> OVS_ACTION_ATTR_TRUNC
>
> As you note, these can consume SKB so also don't bother setting err,
> because they will need to return anyway:
>
> OVS_ACTION_ATTR_USERSPACE
> OVS_ACTION_ATTR_OUTPUT
> OVS_ACTION_ATTR_DROP
>
> And even the following does a weird thing:
>
> OVS_ACTION_ATTR_CT
>
> because sometimes it will consume, and sometimes not.
>
> I think if there isn't a possibility of error being generated (and I
> guess from the code I see there isn't), then it shouldn't return a
> useless code, since err will be 0 on each iteration of the loop.
>

Oh, so you meant it's actualy not being set. Now I get you.
Yes. I figured that could change in the future so I left the structure
of returning an error just in case, but it's true that currently the
function cannot fail.

I'll get rid of it.

> >> > +}
> >> > +
> >> >  /* 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 +1547,11 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
> >> >  			ovs_kfree_skb_reason(skb, reason);
> >> >  			return 0;
> >> >  		}
> >> > +
> >> > +		case OVS_ACTION_ATTR_EMIT_SAMPLE:
> >> > +			err = execute_emit_sample(dp, skb, key, a);
> >> > +			OVS_CB(skb)->cutlen = 0;
> >> > +			break;
> >> >  		}
> >> >
> >> >  		if (unlikely(err)) {
> >> > diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
> >> > index f224d9bcea5e..eb59ff9c8154 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_EMIT_SAMPLE:
> >> >  			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 +3158,29 @@ static int validate_and_copy_check_pkt_len(struct net *net,
> >> >  	return 0;
> >> >  }
> >> >
> >> > +static int validate_emit_sample(const struct nlattr *attr)
> >> > +{
> >> > +	static const struct nla_policy policy[OVS_EMIT_SAMPLE_ATTR_MAX + 1] = {
> >> > +		[OVS_EMIT_SAMPLE_ATTR_GROUP] = { .type = NLA_U32 },
> >> > +		[OVS_EMIT_SAMPLE_ATTR_COOKIE] = {
> >> > +			.type = NLA_BINARY,
> >> > +			.len = OVS_EMIT_SAMPLE_COOKIE_MAX_SIZE
> >> > +		},
> >> > +	};
> >> > +	struct nlattr *a[OVS_EMIT_SAMPLE_ATTR_MAX  + 1];
> >> > +	int err;
> >> > +
> >> > +	if (!IS_ENABLED(CONFIG_PSAMPLE))
> >> > +		return -EOPNOTSUPP;
> >> > +
> >> > +	err = nla_parse_nested(a, OVS_EMIT_SAMPLE_ATTR_MAX, attr, policy,
> >> > +			       NULL);
> >> > +	if (err)
> >> > +		return err;
> >> > +
> >> > +	return a[OVS_EMIT_SAMPLE_ATTR_GROUP] ? 0 : -EINVAL;
> >> > +}
> >> > +
> >> >  static int copy_action(const struct nlattr *from,
> >> >  		       struct sw_flow_actions **sfa, bool log)
> >> >  {
> >> > @@ -3212,6 +3236,7 @@ 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_EMIT_SAMPLE] = (u32)-1,
> >> >  		};
> >> >  		const struct ovs_action_push_vlan *vlan;
> >> >  		int type = nla_type(a);
> >> > @@ -3490,6 +3515,12 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
> >> >  				return -EINVAL;
> >> >  			break;
> >> >
> >> > +		case OVS_ACTION_ATTR_EMIT_SAMPLE:
> >> > +			err = validate_emit_sample(a);
> >> > +			if (err)
> >> > +				return err;
> >> > +			break;
> >> > +
> >> >  		default:
> >> >  			OVS_NLERR(log, "Unknown Action type %d", type);
> >> >  			return -EINVAL;
> >>
> >
> > _______________________________________________
> > dev mailing list
> > dev@...nvswitch.org
> > https://mail.openvswitch.org/mailman/listinfo/ovs-dev
>

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