Re: [PATCH net-next v5 05/10] net: openvswitch: add emit_sample action

[Ilya Maximets <i.maximets@ovn.org>]

On 6/25/24 22:51, Adrian Moreno wrote:
> 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@redhat.com>
> ---
>  Documentation/netlink/specs/ovs_flow.yaml | 17 +++++++++
>  include/uapi/linux/openvswitch.h          | 28 ++++++++++++++
>  net/openvswitch/Kconfig                   |  1 +
>  net/openvswitch/actions.c                 | 45 +++++++++++++++++++++++
>  net/openvswitch/flow_netlink.c            | 33 ++++++++++++++++-
>  5 files changed, 123 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..8cfa1b3f6b06 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_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 OVS_EMIT_SAMPLE_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 packet being emitted.
> + */
> +enum ovs_emit_sample_attr {
> +	OVS_EMIT_SAMPLE_ATTR_GROUP = 1,	/* u32 number. */
> +	OVS_EMIT_SAMPLE_ATTR_COOKIE,	/* Optional, user specified cookie. */
> +
> +	/* private: */
> +	__OVS_EMIT_SAMPLE_ATTR_MAX
> +};
> +
> +#define OVS_EMIT_SAMPLE_ATTR_MAX (__OVS_EMIT_SAMPLE_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_EMIT_SAMPLE: 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_EMIT_SAMPLE,  /* Nested OVS_EMIT_SAMPLE_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..1f555cbba312 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 +1304,37 @@ static int execute_dec_ttl(struct sk_buff *skb, struct sw_flow_key *key)
>  	return 0;
>  }
>  
> +static void execute_emit_sample(struct datapath *dp, struct sk_buff *skb,
> +				const struct sw_flow_key *key,

The 'key' is not used in the function.

> +				const struct nlattr *attr)
> +{
> +#if IS_ENABLED(CONFIG_PSAMPLE)

IIUC, the general coding style guideline is to compile out the whole
function, instead of only the parts.  i.e. something like:

#if IS_ENABLED(CONFIG_PSAMPLE)
static void execute_emit_sample(...) {
    <body>
}
#else
#define execute_emit_sample(dp, skb, attr)
#endif


Otherwise, we'll also need to mark the arguments with __maybe_unused.

The rest of the patch looks good to me.

Best regards, Ilya Maximets.