Re: [dpdk-dev] [PATCH v7 1/2] ethdev: extend flow metadata

[Olivier Matz <olivier.matz@6wind.com>]

Hi Slava,

One comment at the end.

On Thu, Oct 31, 2019 at 01:05:20PM +0000, Viacheslav Ovsiienko wrote:
> Currently, metadata can be set on egress path via mbuf tx_metadata field
> with PKT_TX_METADATA flag and RTE_FLOW_ITEM_TYPE_META matches metadata.
> 
> This patch extends the metadata feature usability.
> 
> 1) RTE_FLOW_ACTION_TYPE_SET_META
> 
> When supporting multiple tables, Tx metadata can also be set by a rule and
> matched by another rule. This new action allows metadata to be set as a
> result of flow match.
> 
> 2) Metadata on ingress
> 
> There's also need to support metadata on ingress. Metadata can be set by
> SET_META action and matched by META item like Tx. The final value set by
> the action will be delivered to application via metadata dynamic field of
> mbuf which can be accessed by RTE_FLOW_DYNF_METADATA() macro or with
> rte_flow_dynf_metadata_set() and rte_flow_dynf_metadata_get() helper
> routines. PKT_RX_DYNF_METADATA flag will be set along with the data.
> 
> The mbuf dynamic field must be registered by calling
> rte_flow_dynf_metadata_register() prior to use SET_META action.
> 
> The availability of dynamic mbuf metadata field can be checked
> with rte_flow_dynf_metadata_avail() routine.
> 
> If application is going to engage the metadata feature it registers
> the metadata  dynamic fields, then PMD checks the metadata field
> availability and handles the appropriate fields in datapath.
> 
> For loopback/hairpin packet, metadata set on Rx/Tx may or may not be
> propagated to the other path depending on hardware capability.
> 
> MARK and METADATA look similar and might operate in similar way,
> but not interacting.
> 
> Initially, there were proposed two metadata related actions:
> 
> - RTE_FLOW_ACTION_TYPE_FLAG
> - RTE_FLOW_ACTION_TYPE_MARK
> 
> These actions set the special flag in the packet metadata, MARK action
> stores some specified value in the metadata storage, and, on the packet
> receiving PMD puts the flag and value to the mbuf and applications can
> see the packet was threated inside flow engine according to the appropriate
> RTE flow(s). MARK and FLAG are like some kind of gateway to transfer some
> per-packet information from the flow engine to the application via
> receiving datapath. Also, there is the item of type RTE_FLOW_ITEM_TYPE_MARK
> provided. It allows us to extend the flow match pattern with the capability
> to match the metadata values set by MARK/FLAG actions on other flows.
> 
> From the datapath point of view, the MARK and FLAG are related to the
> receiving side only. It would useful to have the same gateway on the
> transmitting side and there was the feature of type RTE_FLOW_ITEM_TYPE_META
> was proposed. The application can fill the field in mbuf and this value
> will be transferred to some field in the packet metadata inside the flow
> engine. It did not matter whether these metadata fields are shared because
> of MARK and META items belonged to different domains (receiving and
> transmitting) and could be vendor-specific.
> 
> So far, so good, DPDK proposes some entities to control metadata inside
> the flow engine and gateways to exchange these values on a per-packet basis
> via datapaths.
> 
> As we can see, the MARK and META means are not symmetric, there is absent
> action which would allow us to set META value on the transmitting path.
> So, the action of type:
> 
> - RTE_FLOW_ACTION_TYPE_SET_META was proposed.
> 
> The next, applications raise the new requirements for packet metadata.
> The flow ngines are getting more complex, internal switches are introduced,
> multiple ports might be supported within the same flow engine namespace.
> From the DPDK points of view, it means the packets might be sent on one
> eth_dev port and received on the other one, and the packet path inside
> the flow engine entirely belongs to the same hardware device. The simplest
> example is SR-IOV with PF, VFs and the representors. And there is a
> brilliant opportunity to provide some out-of-band channel to transfer
> some extra data from one port to another one, besides the packet data
> itself. And applications would like to use this opportunity.
> 
> It is supposed for application to use trials (with rte_flow_validate)
> to detect which metadata features (FLAG, MARK, META) actually supported
> by PMD and underlying hardware. It might depend on PMD configuration,
> system software, hardware settings, etc., and should be detected
> in run time.
> 
> Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
> Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
> Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
> Acked-by: Ori Kam <orika@mellanox.com>
> ---
> v7: - updated release notes in collateral patch
> 
> v6: - http://patches.dpdk.org/patch/62245/
>     - minor code style issues
>     - is combined in series with followed egress metadata patch
> 
> v5: - http://patches.dpdk.org/patch/62179/
>     - addressed code style issues from comments
>     - Tx metadata deprecation notice removed
>       (dedicated tx_metadata patch is coming)
>     - MBUF_DYNF_METADATA_NAME is splitted into FIELD and FLAG
>       dedicated ones, RTE suffix is added
>     - metadata historic retrospective is added to log message
>     - rebased
> 
> v4: - http://patches.dpdk.org/patch/62065/
>     - documentation comments addressed
>     - deprecation notice for Tx metadata offload flag
>     - rebased
> 
> v3: - http://patches.dpdk.org/patch/61902/
>     - rebased, neat updates
> 
> v2: - http://patches.dpdk.org/patch/60909/
> 
> v1: - http://patches.dpdk.org/patch/56104/
>     - rfc: http://patches.dpdk.org/patch/54271/
> 
>  app/test-pmd/cmdline_flow.c              |  57 ++++++++++++++++-
>  app/test-pmd/util.c                      |   5 ++
>  doc/guides/prog_guide/rte_flow.rst       |  72 ++++++++++++++++-----
>  doc/guides/rel_notes/release_19_11.rst   |  13 ++++
>  lib/librte_ethdev/rte_ethdev_version.map |   3 +
>  lib/librte_ethdev/rte_flow.c             |  40 ++++++++++++
>  lib/librte_ethdev/rte_flow.h             | 103 +++++++++++++++++++++++++++++--
>  lib/librte_mbuf/rte_mbuf_dyn.h           |   8 ++-
>  8 files changed, 279 insertions(+), 22 deletions(-)
> 
> diff --git a/app/test-pmd/cmdline_flow.c b/app/test-pmd/cmdline_flow.c
> index 0d0bc0a..e4ef066 100644
> --- a/app/test-pmd/cmdline_flow.c
> +++ b/app/test-pmd/cmdline_flow.c
> @@ -316,6 +316,9 @@ enum index {
>  	ACTION_RAW_ENCAP_INDEX_VALUE,
>  	ACTION_RAW_DECAP_INDEX,
>  	ACTION_RAW_DECAP_INDEX_VALUE,
> +	ACTION_SET_META,
> +	ACTION_SET_META_DATA,
> +	ACTION_SET_META_MASK,
>  };
>  
>  /** Maximum size for pattern in struct rte_flow_item_raw. */
> @@ -1067,6 +1070,7 @@ struct parse_action_priv {
>  	ACTION_DEC_TCP_ACK,
>  	ACTION_RAW_ENCAP,
>  	ACTION_RAW_DECAP,
> +	ACTION_SET_META,
>  	ZERO,
>  };
>  
> @@ -1265,6 +1269,13 @@ struct parse_action_priv {
>  	ZERO,
>  };
>  
> +static const enum index action_set_meta[] = {
> +	ACTION_SET_META_DATA,
> +	ACTION_SET_META_MASK,
> +	ACTION_NEXT,
> +	ZERO,
> +};
> +
>  static int parse_set_raw_encap_decap(struct context *, const struct token *,
>  				     const char *, unsigned int,
>  				     void *, unsigned int);
> @@ -1329,6 +1340,10 @@ static int parse_vc_action_raw_encap_index(struct context *,
>  static int parse_vc_action_raw_decap_index(struct context *,
>  					   const struct token *, const char *,
>  					   unsigned int, void *, unsigned int);
> +static int parse_vc_action_set_meta(struct context *ctx,
> +				    const struct token *token, const char *str,
> +				    unsigned int len, void *buf,
> +				    unsigned int size);
>  static int parse_destroy(struct context *, const struct token *,
>  			 const char *, unsigned int,
>  			 void *, unsigned int);
> @@ -3378,7 +3393,31 @@ static int comp_set_raw_index(struct context *, const struct token *,
>  		.help = "index of raw_encap/raw_decap data",
>  		.next = NEXT(next_item),
>  		.call = parse_port,
> -	}
> +	},
> +	[ACTION_SET_META] = {
> +		.name = "set_meta",
> +		.help = "set metadata",
> +		.priv = PRIV_ACTION(SET_META,
> +			sizeof(struct rte_flow_action_set_meta)),
> +		.next = NEXT(action_set_meta),
> +		.call = parse_vc_action_set_meta,
> +	},
> +	[ACTION_SET_META_DATA] = {
> +		.name = "data",
> +		.help = "metadata value",
> +		.next = NEXT(action_set_meta, NEXT_ENTRY(UNSIGNED)),
> +		.args = ARGS(ARGS_ENTRY_HTON
> +			     (struct rte_flow_action_set_meta, data)),
> +		.call = parse_vc_conf,
> +	},
> +	[ACTION_SET_META_MASK] = {
> +		.name = "mask",
> +		.help = "mask for metadata value",
> +		.next = NEXT(action_set_meta, NEXT_ENTRY(UNSIGNED)),
> +		.args = ARGS(ARGS_ENTRY_HTON
> +			     (struct rte_flow_action_set_meta, mask)),
> +		.call = parse_vc_conf,
> +	},
>  };
>  
>  /** Remove and return last entry from argument stack. */
> @@ -4818,6 +4857,22 @@ static int comp_set_raw_index(struct context *, const struct token *,
>  	return ret;
>  }
>  
> +static int
> +parse_vc_action_set_meta(struct context *ctx, const struct token *token,
> +			 const char *str, unsigned int len, void *buf,
> +			 unsigned int size)
> +{
> +	int ret;
> +
> +	ret = parse_vc(ctx, token, str, len, buf, size);
> +	if (ret < 0)
> +		return ret;
> +	ret = rte_flow_dynf_metadata_register();
> +	if (ret < 0)
> +		return -1;
> +	return len;
> +}
> +
>  /** Parse tokens for destroy command. */
>  static int
>  parse_destroy(struct context *ctx, const struct token *token,
> diff --git a/app/test-pmd/util.c b/app/test-pmd/util.c
> index f20531d..56075b3 100644
> --- a/app/test-pmd/util.c
> +++ b/app/test-pmd/util.c
> @@ -82,6 +82,11 @@
>  			       mb->vlan_tci, mb->vlan_tci_outer);
>  		else if (ol_flags & PKT_RX_VLAN)
>  			printf(" - VLAN tci=0x%x", mb->vlan_tci);
> +		if (ol_flags & PKT_TX_METADATA)
> +			printf(" - Tx metadata: 0x%x", mb->tx_metadata);
> +		if (ol_flags & PKT_RX_DYNF_METADATA)
> +			printf(" - Rx metadata: 0x%x",
> +			       *RTE_FLOW_DYNF_METADATA(mb));
>  		if (mb->packet_type) {
>  			rte_get_ptype_name(mb->packet_type, buf, sizeof(buf));
>  			printf(" - hw ptype: %s", buf);
> diff --git a/doc/guides/prog_guide/rte_flow.rst b/doc/guides/prog_guide/rte_flow.rst
> index 159ce19..c943aca 100644
> --- a/doc/guides/prog_guide/rte_flow.rst
> +++ b/doc/guides/prog_guide/rte_flow.rst
> @@ -658,6 +658,32 @@ the physical device, with virtual groups in the PMD or not at all.
>     | ``mask`` | ``id``   | zeroed to match any value |
>     +----------+----------+---------------------------+
>  
> +Item: ``META``
> +^^^^^^^^^^^^^^^^^
> +
> +Matches 32 bit metadata item set.
> +
> +On egress, metadata can be set either by mbuf metadata field with
> +PKT_TX_METADATA flag or ``SET_META`` action. On ingress, ``SET_META``
> +action sets metadata for a packet and the metadata will be reported via
> +``metadata`` dynamic field of ``rte_mbuf`` with PKT_RX_DYNF_METADATA flag.
> +
> +- Default ``mask`` matches the specified Rx metadata value.
> +
> +.. _table_rte_flow_item_meta:
> +
> +.. table:: META
> +
> +   +----------+----------+---------------------------------------+
> +   | Field    | Subfield | Value                                 |
> +   +==========+==========+=======================================+
> +   | ``spec`` | ``data`` | 32 bit metadata value                 |
> +   +----------+----------+---------------------------------------+
> +   | ``last`` | ``data`` | upper range value                     |
> +   +----------+----------+---------------------------------------+
> +   | ``mask`` | ``data`` | bit-mask applies to "spec" and "last" |
> +   +----------+----------+---------------------------------------+
> +
>  Data matching item types
>  ~~~~~~~~~~~~~~~~~~~~~~~~
>  
> @@ -1232,21 +1258,6 @@ Matches a PPPoE session protocol identifier.
>  - ``proto_id``: PPP protocol identifier.
>  - Default ``mask`` matches proto_id only.
>  
> -
> -.. _table_rte_flow_item_meta:
> -
> -.. table:: META
> -
> -   +----------+----------+---------------------------------------+
> -   | Field    | Subfield | Value                                 |
> -   +==========+==========+=======================================+
> -   | ``spec`` | ``data`` | 32 bit metadata value                 |
> -   +----------+--------------------------------------------------+
> -   | ``last`` | ``data`` | upper range value                     |
> -   +----------+----------+---------------------------------------+
> -   | ``mask`` | ``data`` | bit-mask applies to "spec" and "last" |
> -   +----------+----------+---------------------------------------+
> -
>  Item: ``NSH``
>  ^^^^^^^^^^^^^
>  
> @@ -2466,6 +2477,37 @@ Value to decrease TCP acknowledgment number by is a big-endian 32 bit integer.
>  
>  Using this action on non-matching traffic will result in undefined behavior.
>  
> +Action: ``SET_META``
> +^^^^^^^^^^^^^^^^^^^^^^^
> +
> +Set metadata. Item ``META`` matches metadata.
> +
> +Metadata set by mbuf metadata field with PKT_TX_METADATA flag on egress will be
> +overridden by this action. On ingress, the metadata will be carried by
> +``metadata`` dynamic field of ``rte_mbuf`` which can be accessed by
> +``RTE_FLOW_DYNF_METADATA()``. PKT_RX_DYNF_METADATA flag will be set along
> +with the data.
> +
> +The mbuf dynamic field must be registered by calling
> +``rte_flow_dynf_metadata_register()`` prior to use ``SET_META`` action.
> +
> +Altering partial bits is supported with ``mask``. For bits which have never been
> +set, unpredictable value will be seen depending on driver implementation. For
> +loopback/hairpin packet, metadata set on Rx/Tx may or may not be propagated to
> +the other path depending on HW capability.
> +
> +.. _table_rte_flow_action_set_meta:
> +
> +.. table:: SET_META
> +
> +   +----------+----------------------------+
> +   | Field    | Value                      |
> +   +==========+============================+
> +   | ``data`` | 32 bit metadata value      |
> +   +----------+----------------------------+
> +   | ``mask`` | bit-mask applies to "data" |
> +   +----------+----------------------------+
> +
>  Negative types
>  ~~~~~~~~~~~~~~
>  
> diff --git a/doc/guides/rel_notes/release_19_11.rst b/doc/guides/rel_notes/release_19_11.rst
> index f6e90cb..963c4f8 100644
> --- a/doc/guides/rel_notes/release_19_11.rst
> +++ b/doc/guides/rel_notes/release_19_11.rst
> @@ -237,6 +237,14 @@ New Features
>    On supported NICs, we can now setup haipin queue which will offload packets
>    from the wire, backto the wire.
>  
> +* **Extended metadata support in rte_flow.**
> +
> +  Flow metadata is extended to both Rx and Tx.
> +
> +  * Tx metadata can also be set by SET_META action of rte_flow.
> +  * Rx metadata is delivered to host via a dynamic field of ``rte_mbuf`` with
> +    PKT_RX_DYNF_METADATA.
> +
>  
>  Removed Items
>  -------------
> @@ -344,6 +352,11 @@ API Changes
>    has been introduced in this release is used when used when all the packets
>    enqueued in the tx adapter are destined for the same Ethernet port & Tx queue.
>  
> +* metadata: RTE_FLOW_ITEM_TYPE_META data endianness altered to host one.
> +  Due to the new dynamic metadata field in mbuf is host-endian either, there
> +  is the minor compatibility issue for applications in case of 32-bit values
> +  supported.
> +
>  * sched: The pipe nodes configuration parameters such as number of pipes,
>    pipe queue sizes, pipe profiles, etc., are moved from port level structure
>    to subport level. This allows different subports of the same port to
> diff --git a/lib/librte_ethdev/rte_ethdev_version.map b/lib/librte_ethdev/rte_ethdev_version.map
> index 48b5389..e593f34 100644
> --- a/lib/librte_ethdev/rte_ethdev_version.map
> +++ b/lib/librte_ethdev/rte_ethdev_version.map
> @@ -291,4 +291,7 @@ EXPERIMENTAL {
>  	rte_eth_rx_hairpin_queue_setup;
>  	rte_eth_tx_hairpin_queue_setup;
>  	rte_eth_dev_hairpin_capability_get;
> +	rte_flow_dynf_metadata_offs;
> +	rte_flow_dynf_metadata_mask;
> +	rte_flow_dynf_metadata_register;
>  };
> diff --git a/lib/librte_ethdev/rte_flow.c b/lib/librte_ethdev/rte_flow.c
> index ca0f680..b0490cd 100644
> --- a/lib/librte_ethdev/rte_flow.c
> +++ b/lib/librte_ethdev/rte_flow.c
> @@ -12,10 +12,18 @@
>  #include <rte_errno.h>
>  #include <rte_branch_prediction.h>
>  #include <rte_string_fns.h>
> +#include <rte_mbuf.h>
> +#include <rte_mbuf_dyn.h>
>  #include "rte_ethdev.h"
>  #include "rte_flow_driver.h"
>  #include "rte_flow.h"
>  
> +/* Mbuf dynamic field name for metadata. */
> +int rte_flow_dynf_metadata_offs = -1;
> +
> +/* Mbuf dynamic field flag bit number for metadata. */
> +uint64_t rte_flow_dynf_metadata_mask;
> +
>  /**
>   * Flow elements description tables.
>   */
> @@ -157,8 +165,40 @@ struct rte_flow_desc_data {
>  	MK_FLOW_ACTION(DEC_TCP_SEQ, sizeof(rte_be32_t)),
>  	MK_FLOW_ACTION(INC_TCP_ACK, sizeof(rte_be32_t)),
>  	MK_FLOW_ACTION(DEC_TCP_ACK, sizeof(rte_be32_t)),
> +	MK_FLOW_ACTION(SET_META, sizeof(struct rte_flow_action_set_meta)),
>  };
>  
> +int
> +rte_flow_dynf_metadata_register(void)
> +{
> +	int offset;
> +	int flag;
> +
> +	static const struct rte_mbuf_dynfield desc_offs = {
> +		.name = RTE_MBUF_DYNFIELD_METADATA_NAME,
> +		.size = sizeof(uint32_t),
> +		.align = __alignof__(uint32_t),
> +	};
> +	static const struct rte_mbuf_dynflag desc_flag = {
> +		.name = RTE_MBUF_DYNFLAG_METADATA_NAME,
> +	};
> +
> +	offset = rte_mbuf_dynfield_register(&desc_offs);
> +	if (offset < 0)
> +		goto error;
> +	flag = rte_mbuf_dynflag_register(&desc_flag);
> +	if (flag < 0)
> +		goto error;
> +	rte_flow_dynf_metadata_offs = offset;
> +	rte_flow_dynf_metadata_mask = (1ULL << flag);
> +	return 0;
> +
> +error:
> +	rte_flow_dynf_metadata_offs = -1;
> +	rte_flow_dynf_metadata_mask = 0ULL;
> +	return -rte_errno;
> +}
> +
>  static int
>  flow_err(uint16_t port_id, int ret, struct rte_flow_error *error)
>  {
> diff --git a/lib/librte_ethdev/rte_flow.h b/lib/librte_ethdev/rte_flow.h
> index 4fee105..f6e050c 100644
> --- a/lib/librte_ethdev/rte_flow.h
> +++ b/lib/librte_ethdev/rte_flow.h
> @@ -28,6 +28,8 @@
>  #include <rte_byteorder.h>
>  #include <rte_esp.h>
>  #include <rte_higig.h>
> +#include <rte_mbuf.h>
> +#include <rte_mbuf_dyn.h>
>  
>  #ifdef __cplusplus
>  extern "C" {
> @@ -418,7 +420,8 @@ enum rte_flow_item_type {
>  	/**
>  	 * [META]
>  	 *
> -	 * Matches a metadata value specified in mbuf metadata field.
> +	 * Matches a metadata value.
> +	 *
>  	 * See struct rte_flow_item_meta.
>  	 */
>  	RTE_FLOW_ITEM_TYPE_META,
> @@ -1263,18 +1266,23 @@ struct rte_flow_item_icmp6_nd_opt_tla_eth {
>  #endif
>  
>  /**
> - * RTE_FLOW_ITEM_TYPE_META.
> + * RTE_FLOW_ITEM_TYPE_META
>   *
> - * Matches a specified metadata value.
> + * Matches a specified metadata value. On egress, metadata can be set either by
> + * mbuf tx_metadata field with PKT_TX_METADATA flag or
> + * RTE_FLOW_ACTION_TYPE_SET_META. On ingress, RTE_FLOW_ACTION_TYPE_SET_META sets
> + * metadata for a packet and the metadata will be reported via mbuf metadata
> + * dynamic field with PKT_RX_DYNF_METADATA flag. The dynamic mbuf field must be
> + * registered in advance by rte_flow_dynf_metadata_register().
>   */
>  struct rte_flow_item_meta {
> -	rte_be32_t data;
> +	uint32_t data;
>  };
>  
>  /** Default mask for RTE_FLOW_ITEM_TYPE_META. */
>  #ifndef __cplusplus
>  static const struct rte_flow_item_meta rte_flow_item_meta_mask = {
> -	.data = RTE_BE32(UINT32_MAX),
> +	.data = UINT32_MAX,
>  };
>  #endif
>  
> @@ -1942,6 +1950,13 @@ enum rte_flow_action_type {
>  	 * undefined behavior.
>  	 */
>  	RTE_FLOW_ACTION_TYPE_DEC_TCP_ACK,
> +
> +	/**
> +	 * Set metadata on ingress or egress path.
> +	 *
> +	 * See struct rte_flow_action_set_meta.
> +	 */
> +	RTE_FLOW_ACTION_TYPE_SET_META,
>  };
>  
>  /**
> @@ -2429,6 +2444,57 @@ struct rte_flow_action_set_mac {
>  	uint8_t mac_addr[RTE_ETHER_ADDR_LEN];
>  };
>  
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this structure may change without prior notice
> + *
> + * RTE_FLOW_ACTION_TYPE_SET_META
> + *
> + * Set metadata. Metadata set by mbuf tx_metadata field with
> + * PKT_TX_METADATA flag on egress will be overridden by this action. On
> + * ingress, the metadata will be carried by mbuf metadata dynamic field
> + * with PKT_RX_DYNF_METADATA flag if set.  The dynamic mbuf field must be
> + * registered in advance by rte_flow_dynf_metadata_register().
> + *
> + * Altering partial bits is supported with mask. For bits which have never
> + * been set, unpredictable value will be seen depending on driver
> + * implementation. For loopback/hairpin packet, metadata set on Rx/Tx may
> + * or may not be propagated to the other path depending on HW capability.
> + *
> + * RTE_FLOW_ITEM_TYPE_META matches metadata.
> + */
> +struct rte_flow_action_set_meta {
> +	uint32_t data;
> +	uint32_t mask;
> +};
> +
> +/* Mbuf dynamic field offset for metadata. */
> +extern int rte_flow_dynf_metadata_offs;
> +
> +/* Mbuf dynamic field flag mask for metadata. */
> +extern uint64_t rte_flow_dynf_metadata_mask;
> +
> +/* Mbuf dynamic field pointer for metadata. */
> +#define RTE_FLOW_DYNF_METADATA(m) \
> +	RTE_MBUF_DYNFIELD((m), rte_flow_dynf_metadata_offs, uint32_t *)
> +
> +/* Mbuf dynamic flag for metadata. */
> +#define PKT_RX_DYNF_METADATA (rte_flow_dynf_metadata_mask)
> +
> +__rte_experimental
> +static inline uint32_t
> +rte_flow_dynf_metadata_get(struct rte_mbuf *m)
> +{
> +	return *RTE_FLOW_DYNF_METADATA(m);
> +}
> +
> +__rte_experimental
> +static inline void
> +rte_flow_dynf_metadata_set(struct rte_mbuf *m, uint32_t v)
> +{
> +	*RTE_FLOW_DYNF_METADATA(m) = v;
> +}
> +
>  /*
>   * Definition of a single action.
>   *
> @@ -2662,6 +2728,33 @@ enum rte_flow_conv_op {
>  };
>  
>  /**
> + * Check if mbuf dynamic field for metadata is registered.
> + *
> + * @return
> + *   True if registered, false otherwise.
> + */
> +__rte_experimental
> +static inline int
> +rte_flow_dynf_metadata_avail(void)
> +{
> +	return !!rte_flow_dynf_metadata_mask;
> +}
> +
> +/**
> + * Register mbuf dynamic field and flag for metadata.
> + *
> + * This function must be called prior to use SET_META action in order to
> + * register the dynamic mbuf field. Otherwise, the data cannot be delivered to
> + * application.
> + *
> + * @return
> + *   0 on success, a negative errno value otherwise and rte_errno is set.
> + */
> +__rte_experimental
> +int
> +rte_flow_dynf_metadata_register(void);
> +
> +/**
>   * Check whether a flow rule can be created on a given port.
>   *
>   * The flow rule is validated for correctness and whether it could be accepted
> diff --git a/lib/librte_mbuf/rte_mbuf_dyn.h b/lib/librte_mbuf/rte_mbuf_dyn.h
> index 2e9d418..de651c1 100644
> --- a/lib/librte_mbuf/rte_mbuf_dyn.h
> +++ b/lib/librte_mbuf/rte_mbuf_dyn.h
> @@ -234,6 +234,12 @@ int rte_mbuf_dynflag_lookup(const char *name,
>  __rte_experimental
>  void rte_mbuf_dyn_dump(FILE *out);
>  
> -/* Placeholder for dynamic fields and flags declarations. */
> +/*
> + * Placeholder for dynamic fields and flags declarations.
> + * This is centralizing point to gather all field names
> + * and parameters together.
> + */
> +#define RTE_MBUF_DYNFIELD_METADATA_NAME "rte_flow_dynfield_metadata"
> +#define RTE_MBUF_DYNFLAG_METADATA_NAME "rte_flow_dynflag_metadata"
>  

Sorry if it was not clear in my first comment, but I think we should
have some words in this file about what are these field/flag.

After that:
Acked-by: Olivier Matz <olivier.matz@6wind.com>