tools/testing/selftests/bpf/test_lwt_seg6local.c - linux - Git at Google

 #include <stddef.h>
 #include <inttypes.h>
 #include <errno.h>
 #include <linux/seg6_local.h>
 #include <linux/bpf.h>
 #include "bpf_helpers.h"
 #include "bpf_endian.h"

 #define bpf_printk(fmt, ...)				\
 ({							\
 	char ____fmt[] = fmt;				\
 	bpf_trace_printk(____fmt, sizeof(____fmt),	\
 			##__VA_ARGS__);			\
 })

 /* Packet parsing state machine helpers. */
 #define cursor_advance(_cursor, _len) \
 	({ void *_tmp = _cursor; _cursor += _len; _tmp; })

 #define SR6_FLAG_ALERT (1 << 4)

 #define htonll(x) ((bpf_htonl(1)) == 1 ? (x) : ((uint64_t)bpf_htonl((x) & \
 				0xFFFFFFFF) << 32) | bpf_htonl((x) >> 32))
 #define ntohll(x) ((bpf_ntohl(1)) == 1 ? (x) : ((uint64_t)bpf_ntohl((x) & \
 				0xFFFFFFFF) << 32) | bpf_ntohl((x) >> 32))
 #define BPF_PACKET_HEADER __attribute__((packed))

 struct ip6_t {
 	unsigned int ver:4;
 	unsigned int priority:8;
 	unsigned int flow_label:20;
 	unsigned short payload_len;
 	unsigned char next_header;
 	unsigned char hop_limit;
 	unsigned long long src_hi;
 	unsigned long long src_lo;
 	unsigned long long dst_hi;
 	unsigned long long dst_lo;
 } BPF_PACKET_HEADER;

 struct ip6_addr_t {
 	unsigned long long hi;
 	unsigned long long lo;
 } BPF_PACKET_HEADER;

 struct ip6_srh_t {
 	unsigned char nexthdr;
 	unsigned char hdrlen;
 	unsigned char type;
 	unsigned char segments_left;
 	unsigned char first_segment;
 	unsigned char flags;
 	unsigned short tag;

 	struct ip6_addr_t segments[0];
 } BPF_PACKET_HEADER;

 struct sr6_tlv_t {
 	unsigned char type;
 	unsigned char len;
 	unsigned char value[0];
 } BPF_PACKET_HEADER;

 __attribute__((always_inline)) struct ip6_srh_t *get_srh(struct __sk_buff *skb)
 {
 	void *cursor, *data_end;
 	struct ip6_srh_t *srh;
 	struct ip6_t *ip;
 	uint8_t *ipver;

 	data_end = (void *)(long)skb->data_end;
 	cursor = (void *)(long)skb->data;
 	ipver = (uint8_t *)cursor;

 	if ((void *)ipver + sizeof(*ipver) > data_end)
 		return NULL;

 	if ((*ipver >> 4) != 6)
 		return NULL;

 	ip = cursor_advance(cursor, sizeof(*ip));
 	if ((void *)ip + sizeof(*ip) > data_end)
 		return NULL;

 	if (ip->next_header != 43)
 		return NULL;

 	srh = cursor_advance(cursor, sizeof(*srh));
 	if ((void *)srh + sizeof(*srh) > data_end)
 		return NULL;

 	if (srh->type != 4)
 		return NULL;

 	return srh;
 }

 __attribute__((always_inline))
 int update_tlv_pad(struct __sk_buff *skb, uint32_t new_pad,
 		   uint32_t old_pad, uint32_t pad_off)
 {
 	int err;

 	if (new_pad != old_pad) {
 		err = bpf_lwt_seg6_adjust_srh(skb, pad_off,
 					  (int) new_pad - (int) old_pad);
 		if (err)
 			return err;
 	}

 	if (new_pad > 0) {
 		char pad_tlv_buf[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 					0, 0, 0};
 		struct sr6_tlv_t *pad_tlv = (struct sr6_tlv_t *) pad_tlv_buf;

 		pad_tlv->type = SR6_TLV_PADDING;
 		pad_tlv->len = new_pad - 2;

 		err = bpf_lwt_seg6_store_bytes(skb, pad_off,
 					       (void *)pad_tlv_buf, new_pad);
 		if (err)
 			return err;
 	}

 	return 0;
 }

 __attribute__((always_inline))
 int is_valid_tlv_boundary(struct __sk_buff *skb, struct ip6_srh_t *srh,
 			  uint32_t *tlv_off, uint32_t *pad_size,
 			  uint32_t *pad_off)
 {
 	uint32_t srh_off, cur_off;
 	int offset_valid = 0;
 	int err;

 	srh_off = (char *)srh - (char *)(long)skb->data;
 	// cur_off = end of segments, start of possible TLVs
 	cur_off = srh_off + sizeof(*srh) +
 		sizeof(struct ip6_addr_t) * (srh->first_segment + 1);

 	*pad_off = 0;

 	// we can only go as far as ~10 TLVs due to the BPF max stack size
 	#pragma clang loop unroll(full)
 	for (int i = 0; i < 10; i++) {
 		struct sr6_tlv_t tlv;

 		if (cur_off == *tlv_off)
 			offset_valid = 1;

 		if (cur_off >= srh_off + ((srh->hdrlen + 1) << 3))
 			break;

 		err = bpf_skb_load_bytes(skb, cur_off, &tlv, sizeof(tlv));
 		if (err)
 			return err;

 		if (tlv.type == SR6_TLV_PADDING) {
 			*pad_size = tlv.len + sizeof(tlv);
 			*pad_off = cur_off;

 			if (*tlv_off == srh_off) {
 				*tlv_off = cur_off;
 				offset_valid = 1;
 			}
 			break;

 		} else if (tlv.type == SR6_TLV_HMAC) {
 			break;
 		}

 		cur_off += sizeof(tlv) + tlv.len;
 	} // we reached the padding or HMAC TLVs, or the end of the SRH

 	if (*pad_off == 0)
 		*pad_off = cur_off;

 	if (*tlv_off == -1)
 		*tlv_off = cur_off;
 	else if (!offset_valid)
 		return -EINVAL;

 	return 0;
 }

 __attribute__((always_inline))
 int add_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh, uint32_t tlv_off,
 	    struct sr6_tlv_t *itlv, uint8_t tlv_size)
 {
 	uint32_t srh_off = (char *)srh - (char *)(long)skb->data;
 	uint8_t len_remaining, new_pad;
 	uint32_t pad_off = 0;
 	uint32_t pad_size = 0;
 	uint32_t partial_srh_len;
 	int err;

 	if (tlv_off != -1)
 		tlv_off += srh_off;

 	if (itlv->type == SR6_TLV_PADDING || itlv->type == SR6_TLV_HMAC)
 		return -EINVAL;

 	err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off);
 	if (err)
 		return err;

 	err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, sizeof(*itlv) + itlv->len);
 	if (err)
 		return err;

 	err = bpf_lwt_seg6_store_bytes(skb, tlv_off, (void *)itlv, tlv_size);
 	if (err)
 		return err;

 	// the following can't be moved inside update_tlv_pad because the
 	// bpf verifier has some issues with it
 	pad_off += sizeof(*itlv) + itlv->len;
 	partial_srh_len = pad_off - srh_off;
 	len_remaining = partial_srh_len % 8;
 	new_pad = 8 - len_remaining;

 	if (new_pad == 1) // cannot pad for 1 byte only
 		new_pad = 9;
 	else if (new_pad == 8)
 		new_pad = 0;

 	return update_tlv_pad(skb, new_pad, pad_size, pad_off);
 }

 __attribute__((always_inline))
 int delete_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh,
 	       uint32_t tlv_off)
 {
 	uint32_t srh_off = (char *)srh - (char *)(long)skb->data;
 	uint8_t len_remaining, new_pad;
 	uint32_t partial_srh_len;
 	uint32_t pad_off = 0;
 	uint32_t pad_size = 0;
 	struct sr6_tlv_t tlv;
 	int err;

 	tlv_off += srh_off;

 	err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off);
 	if (err)
 		return err;

 	err = bpf_skb_load_bytes(skb, tlv_off, &tlv, sizeof(tlv));
 	if (err)
 		return err;

 	err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, -(sizeof(tlv) + tlv.len));
 	if (err)
 		return err;

 	pad_off -= sizeof(tlv) + tlv.len;
 	partial_srh_len = pad_off - srh_off;
 	len_remaining = partial_srh_len % 8;
 	new_pad = 8 - len_remaining;
 	if (new_pad == 1) // cannot pad for 1 byte only
 		new_pad = 9;
 	else if (new_pad == 8)
 		new_pad = 0;

 	return update_tlv_pad(skb, new_pad, pad_size, pad_off);
 }

 __attribute__((always_inline))
 int has_egr_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh)
 {
 	int tlv_offset = sizeof(struct ip6_t) + sizeof(struct ip6_srh_t) +
 		((srh->first_segment + 1) << 4);
 	struct sr6_tlv_t tlv;

 	if (bpf_skb_load_bytes(skb, tlv_offset, &tlv, sizeof(struct sr6_tlv_t)))
 		return 0;

 	if (tlv.type == SR6_TLV_EGRESS && tlv.len == 18) {
 		struct ip6_addr_t egr_addr;

 		if (bpf_skb_load_bytes(skb, tlv_offset + 4, &egr_addr, 16))
 			return 0;

 		// check if egress TLV value is correct
 		if (ntohll(egr_addr.hi) == 0xfd00000000000000 &&
 				ntohll(egr_addr.lo) == 0x4)
 			return 1;
 	}

 	return 0;
 }

 // This function will push a SRH with segments fd00::1, fd00::2, fd00::3,
 // fd00::4
 SEC("encap_srh")
 int __encap_srh(struct __sk_buff *skb)
 {
 	unsigned long long hi = 0xfd00000000000000;
 	struct ip6_addr_t *seg;
 	struct ip6_srh_t *srh;
 	char srh_buf[72]; // room for 4 segments
 	int err;

 	srh = (struct ip6_srh_t *)srh_buf;
 	srh->nexthdr = 0;
 	srh->hdrlen = 8;
 	srh->type = 4;
 	srh->segments_left = 3;
 	srh->first_segment = 3;
 	srh->flags = 0;
 	srh->tag = 0;

 	seg = (struct ip6_addr_t *)((char *)srh + sizeof(*srh));

 	#pragma clang loop unroll(full)
 	for (unsigned long long lo = 0; lo < 4; lo++) {
 		seg->lo = htonll(4 - lo);
 		seg->hi = htonll(hi);
 		seg = (struct ip6_addr_t *)((char *)seg + sizeof(*seg));
 	}

 	err = bpf_lwt_push_encap(skb, 0, (void *)srh, sizeof(srh_buf));
 	if (err)
 		return BPF_DROP;

 	return BPF_REDIRECT;
 }

 // Add an Egress TLV fc00::4, add the flag A,
 // and apply End.X action to fc42::1
 SEC("add_egr_x")
 int __add_egr_x(struct __sk_buff *skb)
 {
 	unsigned long long hi = 0xfc42000000000000;
 	unsigned long long lo = 0x1;
 	struct ip6_srh_t *srh = get_srh(skb);
 	uint8_t new_flags = SR6_FLAG_ALERT;
 	struct ip6_addr_t addr;
 	int err, offset;

 	if (srh == NULL)
 		return BPF_DROP;

 	uint8_t tlv[20] = {2, 18, 0, 0, 0xfd, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
 			   0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x4};

 	err = add_tlv(skb, srh, (srh->hdrlen+1) << 3,
 		      (struct sr6_tlv_t *)&tlv, 20);
 	if (err)
 		return BPF_DROP;

 	offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags);
 	err = bpf_lwt_seg6_store_bytes(skb, offset,
 				       (void *)&new_flags, sizeof(new_flags));
 	if (err)
 		return BPF_DROP;

 	addr.lo = htonll(lo);
 	addr.hi = htonll(hi);
 	err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_X,
 				  (void *)&addr, sizeof(addr));
 	if (err)
 		return BPF_DROP;
 	return BPF_REDIRECT;
 }

 // Pop the Egress TLV, reset the flags, change the tag 2442 and finally do a
 // simple End action
 SEC("pop_egr")
 int __pop_egr(struct __sk_buff *skb)
 {
 	struct ip6_srh_t *srh = get_srh(skb);
 	uint16_t new_tag = bpf_htons(2442);
 	uint8_t new_flags = 0;
 	int err, offset;

 	if (srh == NULL)
 		return BPF_DROP;

 	if (srh->flags != SR6_FLAG_ALERT)
 		return BPF_DROP;

 	if (srh->hdrlen != 11) // 4 segments + Egress TLV + Padding TLV
 		return BPF_DROP;

 	if (!has_egr_tlv(skb, srh))
 		return BPF_DROP;

 	err = delete_tlv(skb, srh, 8 + (srh->first_segment + 1) * 16);
 	if (err)
 		return BPF_DROP;

 	offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags);
 	if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_flags,
 				     sizeof(new_flags)))
 		return BPF_DROP;

 	offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, tag);
 	if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_tag,
 				     sizeof(new_tag)))
 		return BPF_DROP;

 	return BPF_OK;
 }

 // Inspect if the Egress TLV and flag have been removed, if the tag is correct,
 // then apply a End.T action to reach the last segment
 SEC("inspect_t")
 int __inspect_t(struct __sk_buff *skb)
 {
 	struct ip6_srh_t *srh = get_srh(skb);
 	int table = 117;
 	int err;

 	if (srh == NULL)
 		return BPF_DROP;

 	if (srh->flags != 0)
 		return BPF_DROP;

 	if (srh->tag != bpf_htons(2442))
 		return BPF_DROP;

 	if (srh->hdrlen != 8) // 4 segments
 		return BPF_DROP;

 	err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_T,
 				  (void *)&table, sizeof(table));

 	if (err)
 		return BPF_DROP;

 	return BPF_REDIRECT;
 }

 char __license[] SEC("license") = "GPL";
	#include <stddef.h>
	#include <inttypes.h>
	#include <errno.h>
	#include <linux/seg6_local.h>
	#include <linux/bpf.h>
	#include "bpf_helpers.h"
	#include "bpf_endian.h"

	#define bpf_printk(fmt, ...) \
	({ \
	char ____fmt[] = fmt; \
	bpf_trace_printk(____fmt, sizeof(____fmt), \
	##__VA_ARGS__); \
	})

	/* Packet parsing state machine helpers. */
	#define cursor_advance(_cursor, _len) \
	({ void *_tmp = _cursor; _cursor += _len; _tmp; })

	#define SR6_FLAG_ALERT (1 << 4)

	#define htonll(x) ((bpf_htonl(1)) == 1 ? (x) : ((uint64_t)bpf_htonl((x) & \
	0xFFFFFFFF) << 32) \| bpf_htonl((x) >> 32))
	#define ntohll(x) ((bpf_ntohl(1)) == 1 ? (x) : ((uint64_t)bpf_ntohl((x) & \
	0xFFFFFFFF) << 32) \| bpf_ntohl((x) >> 32))
	#define BPF_PACKET_HEADER __attribute__((packed))

	struct ip6_t {
	unsigned int ver:4;
	unsigned int priority:8;
	unsigned int flow_label:20;
	unsigned short payload_len;
	unsigned char next_header;
	unsigned char hop_limit;
	unsigned long long src_hi;
	unsigned long long src_lo;
	unsigned long long dst_hi;
	unsigned long long dst_lo;
	} BPF_PACKET_HEADER;

	struct ip6_addr_t {
	unsigned long long hi;
	unsigned long long lo;
	} BPF_PACKET_HEADER;

	struct ip6_srh_t {
	unsigned char nexthdr;
	unsigned char hdrlen;
	unsigned char type;
	unsigned char segments_left;
	unsigned char first_segment;
	unsigned char flags;
	unsigned short tag;

	struct ip6_addr_t segments[0];
	} BPF_PACKET_HEADER;

	struct sr6_tlv_t {
	unsigned char type;
	unsigned char len;
	unsigned char value[0];
	} BPF_PACKET_HEADER;

	__attribute__((always_inline)) struct ip6_srh_t get_srh(struct __sk_buff skb)
	{
	void cursor, data_end;
	struct ip6_srh_t *srh;
	struct ip6_t *ip;
	uint8_t *ipver;

	data_end = (void *)(long)skb->data_end;
	cursor = (void *)(long)skb->data;
	ipver = (uint8_t *)cursor;

	if ((void )ipver + sizeof(ipver) > data_end)
	return NULL;

	if ((*ipver >> 4) != 6)
	return NULL;

	ip = cursor_advance(cursor, sizeof(*ip));
	if ((void )ip + sizeof(ip) > data_end)
	return NULL;

	if (ip->next_header != 43)
	return NULL;

	srh = cursor_advance(cursor, sizeof(*srh));
	if ((void )srh + sizeof(srh) > data_end)
	return NULL;

	if (srh->type != 4)
	return NULL;

	return srh;
	}

	__attribute__((always_inline))
	int update_tlv_pad(struct __sk_buff *skb, uint32_t new_pad,
	uint32_t old_pad, uint32_t pad_off)
	{
	int err;

	if (new_pad != old_pad) {
	err = bpf_lwt_seg6_adjust_srh(skb, pad_off,
	(int) new_pad - (int) old_pad);
	if (err)
	return err;
	}

	if (new_pad > 0) {
	char pad_tlv_buf[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0, 0, 0};
	struct sr6_tlv_t pad_tlv = (struct sr6_tlv_t ) pad_tlv_buf;

	pad_tlv->type = SR6_TLV_PADDING;
	pad_tlv->len = new_pad - 2;

	err = bpf_lwt_seg6_store_bytes(skb, pad_off,
	(void *)pad_tlv_buf, new_pad);
	if (err)
	return err;
	}

	return 0;
	}

	__attribute__((always_inline))
	int is_valid_tlv_boundary(struct __sk_buff skb, struct ip6_srh_t srh,
	uint32_t tlv_off, uint32_t pad_size,
	uint32_t *pad_off)
	{
	uint32_t srh_off, cur_off;
	int offset_valid = 0;
	int err;

	srh_off = (char )srh - (char )(long)skb->data;
	// cur_off = end of segments, start of possible TLVs
	cur_off = srh_off + sizeof(*srh) +
	sizeof(struct ip6_addr_t) * (srh->first_segment + 1);

	*pad_off = 0;

	// we can only go as far as ~10 TLVs due to the BPF max stack size
	#pragma clang loop unroll(full)
	for (int i = 0; i < 10; i++) {
	struct sr6_tlv_t tlv;

	if (cur_off == *tlv_off)
	offset_valid = 1;

	if (cur_off >= srh_off + ((srh->hdrlen + 1) << 3))
	break;

	err = bpf_skb_load_bytes(skb, cur_off, &tlv, sizeof(tlv));
	if (err)
	return err;

	if (tlv.type == SR6_TLV_PADDING) {
	*pad_size = tlv.len + sizeof(tlv);
	*pad_off = cur_off;

	if (*tlv_off == srh_off) {
	*tlv_off = cur_off;
	offset_valid = 1;
	}
	break;

	} else if (tlv.type == SR6_TLV_HMAC) {
	break;
	}

	cur_off += sizeof(tlv) + tlv.len;
	} // we reached the padding or HMAC TLVs, or the end of the SRH

	if (*pad_off == 0)
	*pad_off = cur_off;

	if (*tlv_off == -1)
	*tlv_off = cur_off;
	else if (!offset_valid)
	return -EINVAL;

	return 0;
	}

	__attribute__((always_inline))
	int add_tlv(struct __sk_buff skb, struct ip6_srh_t srh, uint32_t tlv_off,
	struct sr6_tlv_t *itlv, uint8_t tlv_size)
	{
	uint32_t srh_off = (char )srh - (char )(long)skb->data;
	uint8_t len_remaining, new_pad;
	uint32_t pad_off = 0;
	uint32_t pad_size = 0;
	uint32_t partial_srh_len;
	int err;

	if (tlv_off != -1)
	tlv_off += srh_off;

	if (itlv->type == SR6_TLV_PADDING \|\| itlv->type == SR6_TLV_HMAC)
	return -EINVAL;

	err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off);
	if (err)
	return err;

	err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, sizeof(*itlv) + itlv->len);
	if (err)
	return err;

	err = bpf_lwt_seg6_store_bytes(skb, tlv_off, (void *)itlv, tlv_size);
	if (err)
	return err;

	// the following can't be moved inside update_tlv_pad because the
	// bpf verifier has some issues with it
	pad_off += sizeof(*itlv) + itlv->len;
	partial_srh_len = pad_off - srh_off;
	len_remaining = partial_srh_len % 8;
	new_pad = 8 - len_remaining;

	if (new_pad == 1) // cannot pad for 1 byte only
	new_pad = 9;
	else if (new_pad == 8)
	new_pad = 0;

	return update_tlv_pad(skb, new_pad, pad_size, pad_off);
	}

	__attribute__((always_inline))
	int delete_tlv(struct __sk_buff skb, struct ip6_srh_t srh,
	uint32_t tlv_off)
	{
	uint32_t srh_off = (char )srh - (char )(long)skb->data;
	uint8_t len_remaining, new_pad;
	uint32_t partial_srh_len;
	uint32_t pad_off = 0;
	uint32_t pad_size = 0;
	struct sr6_tlv_t tlv;
	int err;

	tlv_off += srh_off;

	err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off);
	if (err)
	return err;

	err = bpf_skb_load_bytes(skb, tlv_off, &tlv, sizeof(tlv));
	if (err)
	return err;

	err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, -(sizeof(tlv) + tlv.len));
	if (err)
	return err;

	pad_off -= sizeof(tlv) + tlv.len;
	partial_srh_len = pad_off - srh_off;
	len_remaining = partial_srh_len % 8;
	new_pad = 8 - len_remaining;
	if (new_pad == 1) // cannot pad for 1 byte only
	new_pad = 9;
	else if (new_pad == 8)
	new_pad = 0;

	return update_tlv_pad(skb, new_pad, pad_size, pad_off);
	}

	__attribute__((always_inline))
	int has_egr_tlv(struct __sk_buff skb, struct ip6_srh_t srh)
	{
	int tlv_offset = sizeof(struct ip6_t) + sizeof(struct ip6_srh_t) +
	((srh->first_segment + 1) << 4);
	struct sr6_tlv_t tlv;

	if (bpf_skb_load_bytes(skb, tlv_offset, &tlv, sizeof(struct sr6_tlv_t)))
	return 0;

	if (tlv.type == SR6_TLV_EGRESS && tlv.len == 18) {
	struct ip6_addr_t egr_addr;

	if (bpf_skb_load_bytes(skb, tlv_offset + 4, &egr_addr, 16))
	return 0;

	// check if egress TLV value is correct
	if (ntohll(egr_addr.hi) == 0xfd00000000000000 &&
	ntohll(egr_addr.lo) == 0x4)
	return 1;
	}

	return 0;
	}

	// This function will push a SRH with segments fd00::1, fd00::2, fd00::3,
	// fd00::4
	SEC("encap_srh")
	int __encap_srh(struct __sk_buff *skb)
	{
	unsigned long long hi = 0xfd00000000000000;
	struct ip6_addr_t *seg;
	struct ip6_srh_t *srh;
	char srh_buf[72]; // room for 4 segments
	int err;

	srh = (struct ip6_srh_t *)srh_buf;
	srh->nexthdr = 0;
	srh->hdrlen = 8;
	srh->type = 4;
	srh->segments_left = 3;
	srh->first_segment = 3;
	srh->flags = 0;
	srh->tag = 0;

	seg = (struct ip6_addr_t )((char )srh + sizeof(*srh));

	#pragma clang loop unroll(full)
	for (unsigned long long lo = 0; lo < 4; lo++) {
	seg->lo = htonll(4 - lo);
	seg->hi = htonll(hi);
	seg = (struct ip6_addr_t )((char )seg + sizeof(*seg));
	}

	err = bpf_lwt_push_encap(skb, 0, (void *)srh, sizeof(srh_buf));
	if (err)
	return BPF_DROP;

	return BPF_REDIRECT;
	}

	// Add an Egress TLV fc00::4, add the flag A,
	// and apply End.X action to fc42::1
	SEC("add_egr_x")
	int __add_egr_x(struct __sk_buff *skb)
	{
	unsigned long long hi = 0xfc42000000000000;
	unsigned long long lo = 0x1;
	struct ip6_srh_t *srh = get_srh(skb);
	uint8_t new_flags = SR6_FLAG_ALERT;
	struct ip6_addr_t addr;
	int err, offset;

	if (srh == NULL)
	return BPF_DROP;

	uint8_t tlv[20] = {2, 18, 0, 0, 0xfd, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
	0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x4};

	err = add_tlv(skb, srh, (srh->hdrlen+1) << 3,
	(struct sr6_tlv_t *)&tlv, 20);
	if (err)
	return BPF_DROP;

	offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags);
	err = bpf_lwt_seg6_store_bytes(skb, offset,
	(void *)&new_flags, sizeof(new_flags));
	if (err)
	return BPF_DROP;

	addr.lo = htonll(lo);
	addr.hi = htonll(hi);
	err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_X,
	(void *)&addr, sizeof(addr));
	if (err)
	return BPF_DROP;
	return BPF_REDIRECT;
	}

	// Pop the Egress TLV, reset the flags, change the tag 2442 and finally do a
	// simple End action
	SEC("pop_egr")
	int __pop_egr(struct __sk_buff *skb)
	{
	struct ip6_srh_t *srh = get_srh(skb);
	uint16_t new_tag = bpf_htons(2442);
	uint8_t new_flags = 0;
	int err, offset;

	if (srh == NULL)
	return BPF_DROP;

	if (srh->flags != SR6_FLAG_ALERT)
	return BPF_DROP;

	if (srh->hdrlen != 11) // 4 segments + Egress TLV + Padding TLV
	return BPF_DROP;

	if (!has_egr_tlv(skb, srh))
	return BPF_DROP;

	err = delete_tlv(skb, srh, 8 + (srh->first_segment + 1) * 16);
	if (err)
	return BPF_DROP;

	offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags);
	if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_flags,
	sizeof(new_flags)))
	return BPF_DROP;

	offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, tag);
	if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_tag,
	sizeof(new_tag)))
	return BPF_DROP;

	return BPF_OK;
	}

	// Inspect if the Egress TLV and flag have been removed, if the tag is correct,
	// then apply a End.T action to reach the last segment
	SEC("inspect_t")
	int __inspect_t(struct __sk_buff *skb)
	{
	struct ip6_srh_t *srh = get_srh(skb);
	int table = 117;
	int err;

	if (srh == NULL)
	return BPF_DROP;

	if (srh->flags != 0)
	return BPF_DROP;

	if (srh->tag != bpf_htons(2442))
	return BPF_DROP;

	if (srh->hdrlen != 8) // 4 segments
	return BPF_DROP;

	err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_T,
	(void *)&table, sizeof(table));

	if (err)
	return BPF_DROP;

	return BPF_REDIRECT;
	}

	char __license[] SEC("license") = "GPL";