net/dsa/tag.h - linux - Git at Google

 /* SPDX-License-Identifier: GPL-2.0-or-later */

 #ifndef __DSA_TAG_H
 #define __DSA_TAG_H

 #include <linux/if_vlan.h>
 #include <linux/list.h>
 #include <linux/types.h>
 #include <net/dsa.h>

 #include "port.h"
 #include "user.h"

 struct dsa_tag_driver {
 	const struct dsa_device_ops *ops;
 	struct list_head list;
 	struct module *owner;
 };

 extern struct packet_type dsa_pack_type;

 const struct dsa_device_ops *dsa_tag_driver_get_by_id(int tag_protocol);
 const struct dsa_device_ops *dsa_tag_driver_get_by_name(const char *name);
 void dsa_tag_driver_put(const struct dsa_device_ops *ops);
 const char *dsa_tag_protocol_to_str(const struct dsa_device_ops *ops);

 static inline int dsa_tag_protocol_overhead(const struct dsa_device_ops *ops)
 {
 	return ops->needed_headroom + ops->needed_tailroom;
 }

 static inline struct net_device *dsa_conduit_find_user(struct net_device *dev,
 						       int device, int port)
 {
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	struct dsa_switch_tree *dst = cpu_dp->dst;
 	struct dsa_port *dp;

 	list_for_each_entry(dp, &dst->ports, list)
 		if (dp->ds->index == device && dp->index == port &&
 		    dp->type == DSA_PORT_TYPE_USER)
 			return dp->user;

 	return NULL;
 }

 /**
  * dsa_software_untag_vlan_aware_bridge: Software untagging for VLAN-aware bridge
  * @skb: Pointer to received socket buffer (packet)
  * @br: Pointer to bridge upper interface of ingress port
  * @vid: Parsed VID from packet
  *
  * The bridge can process tagged packets. Software like STP/PTP may not. The
  * bridge can also process untagged packets, to the same effect as if they were
  * tagged with the PVID of the ingress port. So packets tagged with the PVID of
  * the bridge port must be software-untagged, to support both use cases.
  */
 static inline void dsa_software_untag_vlan_aware_bridge(struct sk_buff *skb,
 							struct net_device *br,
 							u16 vid)
 {
 	u16 pvid, proto;
 	int err;

 	err = br_vlan_get_proto(br, &proto);
 	if (err)
 		return;

 	err = br_vlan_get_pvid_rcu(skb->dev, &pvid);
 	if (err)
 		return;

 	if (vid == pvid && skb->vlan_proto == htons(proto))
 		__vlan_hwaccel_clear_tag(skb);
 }

 /**
  * dsa_software_untag_vlan_unaware_bridge: Software untagging for VLAN-unaware bridge
  * @skb: Pointer to received socket buffer (packet)
  * @br: Pointer to bridge upper interface of ingress port
  * @vid: Parsed VID from packet
  *
  * The bridge ignores all VLAN tags. Software like STP/PTP may not (it may run
  * on the plain port, or on a VLAN upper interface). Maybe packets are coming
  * to software as tagged with a driver-defined VID which is NOT equal to the
  * PVID of the bridge port (since the bridge is VLAN-unaware, its configuration
  * should NOT be committed to hardware). DSA needs a method for this private
  * VID to be communicated by software to it, and if packets are tagged with it,
  * software-untag them. Note: the private VID may be different per bridge, to
  * support the FDB isolation use case.
  *
  * FIXME: this is currently implemented based on the broken assumption that
  * the "private VID" used by the driver in VLAN-unaware mode is equal to the
  * bridge PVID. It should not be, except for a coincidence; the bridge PVID is
  * irrelevant to the data path in the VLAN-unaware mode. Thus, the VID that
  * this function removes is wrong.
  *
  * All users of ds->untag_bridge_pvid should fix their drivers, if necessary,
  * to make the two independent. Only then, if there still remains a need to
  * strip the private VID from packets, then a new ds->ops->get_private_vid()
  * API shall be introduced to communicate to DSA what this VID is, which needs
  * to be stripped here.
  */
 static inline void dsa_software_untag_vlan_unaware_bridge(struct sk_buff *skb,
 							  struct net_device *br,
 							  u16 vid)
 {
 	struct net_device *upper_dev;
 	u16 pvid, proto;
 	int err;

 	err = br_vlan_get_proto(br, &proto);
 	if (err)
 		return;

 	err = br_vlan_get_pvid_rcu(skb->dev, &pvid);
 	if (err)
 		return;

 	if (vid != pvid || skb->vlan_proto != htons(proto))
 		return;

 	/* The sad part about attempting to untag from DSA is that we
 	 * don't know, unless we check, if the skb will end up in
 	 * the bridge's data path - br_allowed_ingress() - or not.
 	 * For example, there might be an 8021q upper for the
 	 * default_pvid of the bridge, which will steal VLAN-tagged traffic
 	 * from the bridge's data path. This is a configuration that DSA
 	 * supports because vlan_filtering is 0. In that case, we should
 	 * definitely keep the tag, to make sure it keeps working.
 	 */
 	upper_dev = __vlan_find_dev_deep_rcu(br, htons(proto), vid);
 	if (!upper_dev)
 		__vlan_hwaccel_clear_tag(skb);
 }

 /**
  * dsa_software_vlan_untag: Software VLAN untagging in DSA receive path
  * @skb: Pointer to socket buffer (packet)
  *
  * Receive path method for switches which cannot avoid tagging all packets
  * towards the CPU port. Called when ds->untag_bridge_pvid (legacy) or
  * ds->untag_vlan_aware_bridge_pvid is set to true.
  *
  * As a side effect of this method, any VLAN tag from the skb head is moved
  * to hwaccel.
  */
 static inline struct sk_buff *dsa_software_vlan_untag(struct sk_buff *skb)
 {
 	struct dsa_port *dp = dsa_user_to_port(skb->dev);
 	struct net_device *br = dsa_port_bridge_dev_get(dp);
 	u16 vid;

 	/* software untagging for standalone ports not yet necessary */
 	if (!br)
 		return skb;

 	/* Move VLAN tag from data to hwaccel */
 	if (!skb_vlan_tag_present(skb)) {
 		skb = skb_vlan_untag(skb);
 		if (!skb)
 			return NULL;
 	}

 	if (!skb_vlan_tag_present(skb))
 		return skb;

 	vid = skb_vlan_tag_get_id(skb);

 	if (br_vlan_enabled(br)) {
 		if (dp->ds->untag_vlan_aware_bridge_pvid)
 			dsa_software_untag_vlan_aware_bridge(skb, br, vid);
 	} else {
 		if (dp->ds->untag_bridge_pvid)
 			dsa_software_untag_vlan_unaware_bridge(skb, br, vid);
 	}

 	return skb;
 }

 /* For switches without hardware support for DSA tagging to be able
  * to support termination through the bridge.
  */
 static inline struct net_device *
 dsa_find_designated_bridge_port_by_vid(struct net_device *conduit, u16 vid)
 {
 	struct dsa_port *cpu_dp = conduit->dsa_ptr;
 	struct dsa_switch_tree *dst = cpu_dp->dst;
 	struct bridge_vlan_info vinfo;
 	struct net_device *user;
 	struct dsa_port *dp;
 	int err;

 	list_for_each_entry(dp, &dst->ports, list) {
 		if (dp->type != DSA_PORT_TYPE_USER)
 			continue;

 		if (!dp->bridge)
 			continue;

 		if (dp->stp_state != BR_STATE_LEARNING &&
 		    dp->stp_state != BR_STATE_FORWARDING)
 			continue;

 		/* Since the bridge might learn this packet, keep the CPU port
 		 * affinity with the port that will be used for the reply on
 		 * xmit.
 		 */
 		if (dp->cpu_dp != cpu_dp)
 			continue;

 		user = dp->user;

 		err = br_vlan_get_info_rcu(user, vid, &vinfo);
 		if (err)
 			continue;

 		return user;
 	}

 	return NULL;
 }

 /* If the ingress port offloads the bridge, we mark the frame as autonomously
  * forwarded by hardware, so the software bridge doesn't forward in twice, back
  * to us, because we already did. However, if we're in fallback mode and we do
  * software bridging, we are not offloading it, therefore the dp->bridge
  * pointer is not populated, and flooding needs to be done by software (we are
  * effectively operating in standalone ports mode).
  */
 static inline void dsa_default_offload_fwd_mark(struct sk_buff *skb)
 {
 	struct dsa_port *dp = dsa_user_to_port(skb->dev);

 	skb->offload_fwd_mark = !!(dp->bridge);
 }

 /* Helper for removing DSA header tags from packets in the RX path.
  * Must not be called before skb_pull(len).
  *                                                                 skb->data
  *                                                                         |
  *                                                                         v
  * |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
  * +-----------------------+-----------------------+---------------+-------+
  * |    Destination MAC    |      Source MAC       |  DSA header   | EType |
  * +-----------------------+-----------------------+---------------+-------+
  *                                                 |               |
  * <----- len ----->                               <----- len ----->
  *                 |
  *       >>>>>>>   v
  *       >>>>>>>   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
  *       >>>>>>>   +-----------------------+-----------------------+-------+
  *       >>>>>>>   |    Destination MAC    |      Source MAC       | EType |
  *                 +-----------------------+-----------------------+-------+
  *                                                                         ^
  *                                                                         |
  *                                                                 skb->data
  */
 static inline void dsa_strip_etype_header(struct sk_buff *skb, int len)
 {
 	memmove(skb->data - ETH_HLEN, skb->data - ETH_HLEN - len, 2 * ETH_ALEN);
 }

 /* Helper for creating space for DSA header tags in TX path packets.
  * Must not be called before skb_push(len).
  *
  * Before:
  *
  *       <<<<<<<   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
  * ^     <<<<<<<   +-----------------------+-----------------------+-------+
  * |     <<<<<<<   |    Destination MAC    |      Source MAC       | EType |
  * |               +-----------------------+-----------------------+-------+
  * <----- len ----->
  * |
  * |
  * skb->data
  *
  * After:
  *
  * |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
  * +-----------------------+-----------------------+---------------+-------+
  * |    Destination MAC    |      Source MAC       |  DSA header   | EType |
  * +-----------------------+-----------------------+---------------+-------+
  * ^                                               |               |
  * |                                               <----- len ----->
  * skb->data
  */
 static inline void dsa_alloc_etype_header(struct sk_buff *skb, int len)
 {
 	memmove(skb->data, skb->data + len, 2 * ETH_ALEN);
 }

 /* On RX, eth_type_trans() on the DSA conduit pulls ETH_HLEN bytes starting from
  * skb_mac_header(skb), which leaves skb->data pointing at the first byte after
  * what the DSA conduit perceives as the EtherType (the beginning of the L3
  * protocol). Since DSA EtherType header taggers treat the EtherType as part of
  * the DSA tag itself, and the EtherType is 2 bytes in length, the DSA header
  * is located 2 bytes behind skb->data. Note that EtherType in this context
  * means the first 2 bytes of the DSA header, not the encapsulated EtherType
  * that will become visible after the DSA header is stripped.
  */
 static inline void *dsa_etype_header_pos_rx(struct sk_buff *skb)
 {
 	return skb->data - 2;
 }

 /* On TX, skb->data points to the MAC header, which means that EtherType
  * header taggers start exactly where the EtherType is (the EtherType is
  * treated as part of the DSA header).
  */
 static inline void *dsa_etype_header_pos_tx(struct sk_buff *skb)
 {
 	return skb->data + 2 * ETH_ALEN;
 }

 /* Create 2 modaliases per tagging protocol, one to auto-load the module
  * given the ID reported by get_tag_protocol(), and the other by name.
  */
 #define DSA_TAG_DRIVER_ALIAS "dsa_tag:"
 #define MODULE_ALIAS_DSA_TAG_DRIVER(__proto, __name) \
 	MODULE_ALIAS(DSA_TAG_DRIVER_ALIAS __name); \
 	MODULE_ALIAS(DSA_TAG_DRIVER_ALIAS "id-" \
 		     __stringify(__proto##_VALUE))

 void dsa_tag_drivers_register(struct dsa_tag_driver *dsa_tag_driver_array[],
 			      unsigned int count,
 			      struct module *owner);
 void dsa_tag_drivers_unregister(struct dsa_tag_driver *dsa_tag_driver_array[],
 				unsigned int count);

 #define dsa_tag_driver_module_drivers(__dsa_tag_drivers_array, __count)	\
 static int __init dsa_tag_driver_module_init(void)			\
 {									\
 	dsa_tag_drivers_register(__dsa_tag_drivers_array, __count,	\
 				 THIS_MODULE);				\
 	return 0;							\
 }									\
 module_init(dsa_tag_driver_module_init);				\
 									\
 static void __exit dsa_tag_driver_module_exit(void)			\
 {									\
 	dsa_tag_drivers_unregister(__dsa_tag_drivers_array, __count);	\
 }									\
 module_exit(dsa_tag_driver_module_exit)

 /**
  * module_dsa_tag_drivers() - Helper macro for registering DSA tag
  * drivers
  * @__ops_array: Array of tag driver structures
  *
  * Helper macro for DSA tag drivers which do not do anything special
  * in module init/exit. Each module may only use this macro once, and
  * calling it replaces module_init() and module_exit().
  */
 #define module_dsa_tag_drivers(__ops_array)				\
 dsa_tag_driver_module_drivers(__ops_array, ARRAY_SIZE(__ops_array))

 #define DSA_TAG_DRIVER_NAME(__ops) dsa_tag_driver ## _ ## __ops

 /* Create a static structure we can build a linked list of dsa_tag
  * drivers
  */
 #define DSA_TAG_DRIVER(__ops)						\
 static struct dsa_tag_driver DSA_TAG_DRIVER_NAME(__ops) = {		\
 	.ops = &__ops,							\
 }

 /**
  * module_dsa_tag_driver() - Helper macro for registering a single DSA tag
  * driver
  * @__ops: Single tag driver structures
  *
  * Helper macro for DSA tag drivers which do not do anything special
  * in module init/exit. Each module may only use this macro once, and
  * calling it replaces module_init() and module_exit().
  */
 #define module_dsa_tag_driver(__ops)					\
 DSA_TAG_DRIVER(__ops);							\
 									\
 static struct dsa_tag_driver *dsa_tag_driver_array[] =	{		\
 	&DSA_TAG_DRIVER_NAME(__ops)					\
 };									\
 module_dsa_tag_drivers(dsa_tag_driver_array)

 #endif
	/* SPDX-License-Identifier: GPL-2.0-or-later */

	#ifndef __DSA_TAG_H
	#define __DSA_TAG_H

	#include <linux/if_vlan.h>
	#include <linux/list.h>
	#include <linux/types.h>
	#include <net/dsa.h>

	#include "port.h"
	#include "user.h"

	struct dsa_tag_driver {
	const struct dsa_device_ops *ops;
	struct list_head list;
	struct module *owner;
	};

	extern struct packet_type dsa_pack_type;

	const struct dsa_device_ops *dsa_tag_driver_get_by_id(int tag_protocol);
	const struct dsa_device_ops dsa_tag_driver_get_by_name(const char name);
	void dsa_tag_driver_put(const struct dsa_device_ops *ops);
	const char dsa_tag_protocol_to_str(const struct dsa_device_ops ops);

	static inline int dsa_tag_protocol_overhead(const struct dsa_device_ops *ops)
	{
	return ops->needed_headroom + ops->needed_tailroom;
	}

	static inline struct net_device dsa_conduit_find_user(struct net_device dev,
	int device, int port)
	{
	struct dsa_port *cpu_dp = dev->dsa_ptr;
	struct dsa_switch_tree *dst = cpu_dp->dst;
	struct dsa_port *dp;

	list_for_each_entry(dp, &dst->ports, list)
	if (dp->ds->index == device && dp->index == port &&
	dp->type == DSA_PORT_TYPE_USER)
	return dp->user;

	return NULL;
	}

	/**
	* dsa_software_untag_vlan_aware_bridge: Software untagging for VLAN-aware bridge
	* @skb: Pointer to received socket buffer (packet)
	* @br: Pointer to bridge upper interface of ingress port
	* @vid: Parsed VID from packet
	*
	* The bridge can process tagged packets. Software like STP/PTP may not. The
	* bridge can also process untagged packets, to the same effect as if they were
	* tagged with the PVID of the ingress port. So packets tagged with the PVID of
	* the bridge port must be software-untagged, to support both use cases.
	*/
	static inline void dsa_software_untag_vlan_aware_bridge(struct sk_buff *skb,
	struct net_device *br,
	u16 vid)
	{
	u16 pvid, proto;
	int err;

	err = br_vlan_get_proto(br, &proto);
	if (err)
	return;

	err = br_vlan_get_pvid_rcu(skb->dev, &pvid);
	if (err)
	return;

	if (vid == pvid && skb->vlan_proto == htons(proto))
	__vlan_hwaccel_clear_tag(skb);
	}

	/**
	* dsa_software_untag_vlan_unaware_bridge: Software untagging for VLAN-unaware bridge
	* @skb: Pointer to received socket buffer (packet)
	* @br: Pointer to bridge upper interface of ingress port
	* @vid: Parsed VID from packet
	*
	* The bridge ignores all VLAN tags. Software like STP/PTP may not (it may run
	* on the plain port, or on a VLAN upper interface). Maybe packets are coming
	* to software as tagged with a driver-defined VID which is NOT equal to the
	* PVID of the bridge port (since the bridge is VLAN-unaware, its configuration
	* should NOT be committed to hardware). DSA needs a method for this private
	* VID to be communicated by software to it, and if packets are tagged with it,
	* software-untag them. Note: the private VID may be different per bridge, to
	* support the FDB isolation use case.
	*
	* FIXME: this is currently implemented based on the broken assumption that
	* the "private VID" used by the driver in VLAN-unaware mode is equal to the
	* bridge PVID. It should not be, except for a coincidence; the bridge PVID is
	* irrelevant to the data path in the VLAN-unaware mode. Thus, the VID that
	* this function removes is wrong.
	*
	* All users of ds->untag_bridge_pvid should fix their drivers, if necessary,
	* to make the two independent. Only then, if there still remains a need to
	* strip the private VID from packets, then a new ds->ops->get_private_vid()
	* API shall be introduced to communicate to DSA what this VID is, which needs
	* to be stripped here.
	*/
	static inline void dsa_software_untag_vlan_unaware_bridge(struct sk_buff *skb,
	struct net_device *br,
	u16 vid)
	{
	struct net_device *upper_dev;
	u16 pvid, proto;
	int err;

	err = br_vlan_get_proto(br, &proto);
	if (err)
	return;

	err = br_vlan_get_pvid_rcu(skb->dev, &pvid);
	if (err)
	return;

	if (vid != pvid \|\| skb->vlan_proto != htons(proto))
	return;

	/* The sad part about attempting to untag from DSA is that we
	* don't know, unless we check, if the skb will end up in
	* the bridge's data path - br_allowed_ingress() - or not.
	* For example, there might be an 8021q upper for the
	* default_pvid of the bridge, which will steal VLAN-tagged traffic
	* from the bridge's data path. This is a configuration that DSA
	* supports because vlan_filtering is 0. In that case, we should
	* definitely keep the tag, to make sure it keeps working.
	*/
	upper_dev = __vlan_find_dev_deep_rcu(br, htons(proto), vid);
	if (!upper_dev)
	__vlan_hwaccel_clear_tag(skb);
	}

	/**
	* dsa_software_vlan_untag: Software VLAN untagging in DSA receive path
	* @skb: Pointer to socket buffer (packet)
	*
	* Receive path method for switches which cannot avoid tagging all packets
	* towards the CPU port. Called when ds->untag_bridge_pvid (legacy) or
	* ds->untag_vlan_aware_bridge_pvid is set to true.
	*
	* As a side effect of this method, any VLAN tag from the skb head is moved
	* to hwaccel.
	*/
	static inline struct sk_buff dsa_software_vlan_untag(struct sk_buff skb)
	{
	struct dsa_port *dp = dsa_user_to_port(skb->dev);
	struct net_device *br = dsa_port_bridge_dev_get(dp);
	u16 vid;

	/* software untagging for standalone ports not yet necessary */
	if (!br)
	return skb;

	/* Move VLAN tag from data to hwaccel */
	if (!skb_vlan_tag_present(skb)) {
	skb = skb_vlan_untag(skb);
	if (!skb)
	return NULL;
	}

	if (!skb_vlan_tag_present(skb))
	return skb;

	vid = skb_vlan_tag_get_id(skb);

	if (br_vlan_enabled(br)) {
	if (dp->ds->untag_vlan_aware_bridge_pvid)
	dsa_software_untag_vlan_aware_bridge(skb, br, vid);
	} else {
	if (dp->ds->untag_bridge_pvid)
	dsa_software_untag_vlan_unaware_bridge(skb, br, vid);
	}

	return skb;
	}

	/* For switches without hardware support for DSA tagging to be able
	* to support termination through the bridge.
	*/
	static inline struct net_device *
	dsa_find_designated_bridge_port_by_vid(struct net_device *conduit, u16 vid)
	{
	struct dsa_port *cpu_dp = conduit->dsa_ptr;
	struct dsa_switch_tree *dst = cpu_dp->dst;
	struct bridge_vlan_info vinfo;
	struct net_device *user;
	struct dsa_port *dp;
	int err;

	list_for_each_entry(dp, &dst->ports, list) {
	if (dp->type != DSA_PORT_TYPE_USER)
	continue;

	if (!dp->bridge)
	continue;

	if (dp->stp_state != BR_STATE_LEARNING &&
	dp->stp_state != BR_STATE_FORWARDING)
	continue;

	/* Since the bridge might learn this packet, keep the CPU port
	* affinity with the port that will be used for the reply on
	* xmit.
	*/
	if (dp->cpu_dp != cpu_dp)
	continue;

	user = dp->user;

	err = br_vlan_get_info_rcu(user, vid, &vinfo);
	if (err)
	continue;

	return user;
	}

	return NULL;
	}

	/* If the ingress port offloads the bridge, we mark the frame as autonomously
	* forwarded by hardware, so the software bridge doesn't forward in twice, back
	* to us, because we already did. However, if we're in fallback mode and we do
	* software bridging, we are not offloading it, therefore the dp->bridge
	* pointer is not populated, and flooding needs to be done by software (we are
	* effectively operating in standalone ports mode).
	*/
	static inline void dsa_default_offload_fwd_mark(struct sk_buff *skb)
	{
	struct dsa_port *dp = dsa_user_to_port(skb->dev);

	skb->offload_fwd_mark = !!(dp->bridge);
	}

	/* Helper for removing DSA header tags from packets in the RX path.
	* Must not be called before skb_pull(len).
	* skb->data
	* \|
	* v
	* \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \|
	* +-----------------------+-----------------------+---------------+-------+
	* \| Destination MAC \| Source MAC \| DSA header \| EType \|
	* +-----------------------+-----------------------+---------------+-------+
	* \| \|
	* <----- len -----> <----- len ----->
	* \|
	* >>>>>>> v
	* >>>>>>> \| \| \| \| \| \| \| \| \| \| \| \| \| \| \|
	* >>>>>>> +-----------------------+-----------------------+-------+
	* >>>>>>> \| Destination MAC \| Source MAC \| EType \|
	* +-----------------------+-----------------------+-------+
	* ^
	* \|
	* skb->data
	*/
	static inline void dsa_strip_etype_header(struct sk_buff *skb, int len)
	{
	memmove(skb->data - ETH_HLEN, skb->data - ETH_HLEN - len, 2 * ETH_ALEN);
	}

	/* Helper for creating space for DSA header tags in TX path packets.
	* Must not be called before skb_push(len).
	*
	* Before:
	*
	* <<<<<<< \| \| \| \| \| \| \| \| \| \| \| \| \| \| \|
	* ^ <<<<<<< +-----------------------+-----------------------+-------+
	* \| <<<<<<< \| Destination MAC \| Source MAC \| EType \|
	* \| +-----------------------+-----------------------+-------+
	* <----- len ----->
	* \|
	* \|
	* skb->data
	*
	* After:
	*
	* \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \|
	* +-----------------------+-----------------------+---------------+-------+
	* \| Destination MAC \| Source MAC \| DSA header \| EType \|
	* +-----------------------+-----------------------+---------------+-------+
	* ^ \| \|
	* \| <----- len ----->
	* skb->data
	*/
	static inline void dsa_alloc_etype_header(struct sk_buff *skb, int len)
	{
	memmove(skb->data, skb->data + len, 2 * ETH_ALEN);
	}

	/* On RX, eth_type_trans() on the DSA conduit pulls ETH_HLEN bytes starting from
	* skb_mac_header(skb), which leaves skb->data pointing at the first byte after
	* what the DSA conduit perceives as the EtherType (the beginning of the L3
	* protocol). Since DSA EtherType header taggers treat the EtherType as part of
	* the DSA tag itself, and the EtherType is 2 bytes in length, the DSA header
	* is located 2 bytes behind skb->data. Note that EtherType in this context
	* means the first 2 bytes of the DSA header, not the encapsulated EtherType
	* that will become visible after the DSA header is stripped.
	*/
	static inline void dsa_etype_header_pos_rx(struct sk_buff skb)
	{
	return skb->data - 2;
	}

	/* On TX, skb->data points to the MAC header, which means that EtherType
	* header taggers start exactly where the EtherType is (the EtherType is
	* treated as part of the DSA header).
	*/
	static inline void dsa_etype_header_pos_tx(struct sk_buff skb)
	{
	return skb->data + 2 * ETH_ALEN;
	}

	/* Create 2 modaliases per tagging protocol, one to auto-load the module
	* given the ID reported by get_tag_protocol(), and the other by name.
	*/
	#define DSA_TAG_DRIVER_ALIAS "dsa_tag:"
	#define MODULE_ALIAS_DSA_TAG_DRIVER(__proto, __name) \
	MODULE_ALIAS(DSA_TAG_DRIVER_ALIAS __name); \
	MODULE_ALIAS(DSA_TAG_DRIVER_ALIAS "id-" \
	__stringify(__proto##_VALUE))

	void dsa_tag_drivers_register(struct dsa_tag_driver *dsa_tag_driver_array[],
	unsigned int count,
	struct module *owner);
	void dsa_tag_drivers_unregister(struct dsa_tag_driver *dsa_tag_driver_array[],
	unsigned int count);

	#define dsa_tag_driver_module_drivers(__dsa_tag_drivers_array, __count) \
	static int __init dsa_tag_driver_module_init(void) \
	{ \
	dsa_tag_drivers_register(__dsa_tag_drivers_array, __count, \
	THIS_MODULE); \
	return 0; \
	} \
	module_init(dsa_tag_driver_module_init); \
	\
	static void __exit dsa_tag_driver_module_exit(void) \
	{ \
	dsa_tag_drivers_unregister(__dsa_tag_drivers_array, __count); \
	} \
	module_exit(dsa_tag_driver_module_exit)

	/**
	* module_dsa_tag_drivers() - Helper macro for registering DSA tag
	* drivers
	* @__ops_array: Array of tag driver structures
	*
	* Helper macro for DSA tag drivers which do not do anything special
	* in module init/exit. Each module may only use this macro once, and
	* calling it replaces module_init() and module_exit().
	*/
	#define module_dsa_tag_drivers(__ops_array) \
	dsa_tag_driver_module_drivers(__ops_array, ARRAY_SIZE(__ops_array))

	#define DSA_TAG_DRIVER_NAME(__ops) dsa_tag_driver ## _ ## __ops

	/* Create a static structure we can build a linked list of dsa_tag
	* drivers
	*/
	#define DSA_TAG_DRIVER(__ops) \
	static struct dsa_tag_driver DSA_TAG_DRIVER_NAME(__ops) = { \
	.ops = &__ops, \
	}

	/**
	* module_dsa_tag_driver() - Helper macro for registering a single DSA tag
	* driver
	* @__ops: Single tag driver structures
	*
	* Helper macro for DSA tag drivers which do not do anything special
	* in module init/exit. Each module may only use this macro once, and
	* calling it replaces module_init() and module_exit().
	*/
	#define module_dsa_tag_driver(__ops) \
	DSA_TAG_DRIVER(__ops); \
	\
	static struct dsa_tag_driver *dsa_tag_driver_array[] = { \
	&DSA_TAG_DRIVER_NAME(__ops) \
	}; \
	module_dsa_tag_drivers(dsa_tag_driver_array)

	#endif