[PATCH iproute2-next v1 RESEND 5/6] seg6: add support for the End.M.GTP6.D.Di behavior

[Yuya Kusakabe <yuya.kusakabe@gmail.com>]

Add support for the End.M.GTP6.D.Di drop-in interconnect behavior,
which translates IPv6/GTP-U traffic into an SRv6 SR Policy while
preserving the original outer IPv6 destination as the final SRH
segment.  Unlike End.M.GTP6.D, this behavior does not take
sr_prefix_len.

Example:
ip -6 r a 2001:db8:f::/64 encap seg6local action End.M.GTP6.D.Di \
    srh segs 2001:db8:2::1,2001:db8:3::e \
    src 2001:db8::1 dev sr0

Link: https://datatracker.ietf.org/doc/html/rfc9433

Signed-off-by: Yuya Kusakabe <yuya.kusakabe@gmail.com>
---
 include/uapi/linux/seg6_local.h |  2 ++
 ip/iproute.c                    |  2 +-
 ip/iproute_lwtunnel.c           | 10 ++++++++++
 man/man8/ip-route.8.in          | 16 ++++++++++++++++
 4 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/seg6_local.h b/include/uapi/linux/seg6_local.h
index ed44fb858600..0ca8405df2f2 100644
--- a/include/uapi/linux/seg6_local.h
+++ b/include/uapi/linux/seg6_local.h
@@ -80,6 +80,8 @@ enum {
 	SEG6_LOCAL_ACTION_END_M_GTP6_E	= 19,
 	/* IPv6/GTP-U decap into SRv6 (RFC 9433 Section 6.3) */
 	SEG6_LOCAL_ACTION_END_M_GTP6_D	= 20,
+	/* IPv6/GTP-U decap into SRv6, drop-in mode (RFC 9433 Section 6.4) */
+	SEG6_LOCAL_ACTION_END_M_GTP6_D_DI = 21,
 
 	__SEG6_LOCAL_ACTION_MAX,
 };
diff --git a/ip/iproute.c b/ip/iproute.c
index 8ced32a4f84e..1604545febc8 100644
--- a/ip/iproute.c
+++ b/ip/iproute.c
@@ -107,7 +107,7 @@ static void usage(void)
 		"            End.DT6 | End.DT4 | End.DT46 | End.B6 | End.B6.Encaps |\n"
 		"            End.BM | End.S | End.AS | End.AM | End.BPF |\n"
 		"            End.MAP | End.M.GTP4.E | End.M.GTP6.E |\n"
-		"            End.M.GTP6.D }\n"
+		"            End.M.GTP6.D | End.M.GTP6.D.Di }\n"
 		"OPTIONS := OPTION [ OPTIONS ]\n"
 		"OPTION := { flavors FLAVORS | srh SEG6HDR | nh4 ADDR | nh6 ADDR | iif DEV | oif DEV |\n"
 		"            table TABLEID | vrftable TABLEID | endpoint PROGNAME | MOBILE_OPTION }\n"
diff --git a/ip/iproute_lwtunnel.c b/ip/iproute_lwtunnel.c
index d54bf4628f6f..1234c9f146bf 100644
--- a/ip/iproute_lwtunnel.c
+++ b/ip/iproute_lwtunnel.c
@@ -409,6 +409,7 @@ static const char *seg6_action_names[SEG6_LOCAL_ACTION_MAX + 1] = {
 	[SEG6_LOCAL_ACTION_END_M_GTP4_E]	= "End.M.GTP4.E",
 	[SEG6_LOCAL_ACTION_END_M_GTP6_E]	= "End.M.GTP6.E",
 	[SEG6_LOCAL_ACTION_END_M_GTP6_D]	= "End.M.GTP6.D",
+	[SEG6_LOCAL_ACTION_END_M_GTP6_D_DI]	= "End.M.GTP6.D.Di",
 };
 
 static const char *format_action_type(int action)
@@ -632,6 +633,7 @@ static bool seg6local_action_excludes_final_seg(int action)
 	switch (action) {
 	case SEG6_LOCAL_ACTION_END_B6_ENCAP:
 	case SEG6_LOCAL_ACTION_END_M_GTP6_D:
+	case SEG6_LOCAL_ACTION_END_M_GTP6_D_DI:
 		return true;
 	default:
 		return false;
@@ -663,6 +665,14 @@ static void seg6local_action_check_attrs(int action, int srh_ok, int nh6_ok,
 			invarg("End.M.GTP6.D requires \"srh segs\", \"src\","
 			       " and \"sr_prefix_len\"\n", "");
 		break;
+	case SEG6_LOCAL_ACTION_END_M_GTP6_D_DI:
+		if (!srh_ok || !mobile_src_ok)
+			invarg("End.M.GTP6.D.Di requires \"srh segs\" and \"src\"\n",
+			       "");
+		if (mobile_sr_plen_ok)
+			invarg("End.M.GTP6.D.Di does not accept \"sr_prefix_len\"\n",
+			       "");
+		break;
 	case SEG6_LOCAL_ACTION_END_M_GTP4_E:
 		if (!mobile_src_ok || !mobile_v4mask_ok)
 			invarg("End.M.GTP4.E requires \"src\" and \"v4_mask_len\"\n",
diff --git a/man/man8/ip-route.8.in b/man/man8/ip-route.8.in
index 35e6e2080a1f..0487338707c6 100644
--- a/man/man8/ip-route.8.in
+++ b/man/man8/ip-route.8.in
@@ -1117,6 +1117,22 @@ The action requires either no SRH or an SRH with
 equal to zero on the inbound packet; other matching packets are
 dropped.
 
+.B End.M.GTP6.D.Di srh segs
+.IR SEGMENTS
+.B src
+.IR ADDRESS
+- SRv6 Mobile User Plane End.M.GTP6.D.Di drop-in interconnect behavior
+(RFC 9433 Section 6.4).  Identical to
+.B End.M.GTP6.D
+except that the original outer IPv6 destination address of the
+incoming GTP-U packet is preserved as the final segment of the new
+SRH, allowing existing SRv6 networks to be inserted into a legacy
+mobile path without changing the destination semantics.
+.B sr_prefix_len
+is rejected for this action: the original outer destination is
+preserved verbatim instead of being repacked with an Args.Mob.Session
+field, so no locator length needs to be carried.
+
 .B Flavors parameters
 
 The flavors represent additional operations that can modify or extend a
-- 
2.50.1