[PATCH iproute2-next v2] ip: add OVPN device mode support

[Marco Baffo <marco@mandelbit.com>]

ovpn devices (OpenVPN data channel offload, kernel v6.16) can already
be created with "ip link add ovpn0 type ovpn", but the mode is always
left to the kernel default (p2p mode).

Add ovpn link type support so that point-to-point (p2p) or multi-peer
(mp) mode can be selected at creation time and shown by
"ip -d link show".

Example:

  $ ip link add ovpn0 type ovpn mode mp

Signed-off-by: Marco Baffo <marco@mandelbit.com>
---

Changes in v2:
- Created a mode table to use for both parsing and printing.
- Used strcmp() instead of matches().

 ip/Makefile           |  2 +-
 ip/iplink.c           |  2 +-
 ip/iplink_ovpn.c      | 92 +++++++++++++++++++++++++++++++++++++++++++
 man/man8/ip-link.8.in | 24 +++++++++++
 4 files changed, 118 insertions(+), 2 deletions(-)
 create mode 100644 ip/iplink_ovpn.c

diff --git a/ip/Makefile b/ip/Makefile
index 3535ba78..978f6841 100644
--- a/ip/Makefile
+++ b/ip/Makefile
@@ -13,7 +13,7 @@ IPOBJ=ip.o ipaddress.o ipaddrlabel.o iproute.o iprule.o ipnetns.o \
     ipvrf.o iplink_xstats.o ipseg6.o iplink_netdevsim.o iplink_rmnet.o \
     ipnexthop.o ipmptcp.o iplink_bareudp.o iplink_wwan.o ipioam6.o \
     iplink_amt.o iplink_batadv.o iplink_gtp.o iplink_virt_wifi.o \
-    iplink_netkit.o ipstats.o
+    iplink_netkit.o ipstats.o iplink_ovpn.o
 
 RTMONOBJ=rtmon.o
 
diff --git a/ip/iplink.c b/ip/iplink.c
index 3f0b46c9..c6aee8b6 100644
--- a/ip/iplink.c
+++ b/ip/iplink.c
@@ -42,7 +42,7 @@ void iplink_types_usage(void)
 		"          ifb | ip6erspan | ip6gre | ip6gretap | ip6tnl |\n"
 		"          ipip | ipoib | ipvlan | ipvtap |\n"
 		"          macsec | macvlan | macvtap | netdevsim |\n"
-		"          netkit | nlmon | pfcp | rmnet | sit | team | team_slave |\n"
+		"          netkit | nlmon | ovpn | pfcp | rmnet | sit | team | team_slave |\n"
 		"          vcan | veth | vlan | vrf | vti | vxcan | vxlan | wwan |\n"
 		"          xfrm | virt_wifi }\n");
 }
diff --git a/ip/iplink_ovpn.c b/ip/iplink_ovpn.c
new file mode 100644
index 00000000..d3dff295
--- /dev/null
+++ b/ip/iplink_ovpn.c
@@ -0,0 +1,92 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * iplink_ovpn.c	OpenVPN DCO device support
+ *
+ * Author: Marco Baffo <marco@mandelbit.com>
+ *
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <linux/if_link.h>
+
+#include "utils.h"
+#include "ip_common.h"
+
+static const char * const ovpn_mode_strings[] = {
+	[OVPN_MODE_P2P] = "p2p",
+	[OVPN_MODE_MP] = "mp",
+};
+
+static const char *ovpn_mode_to_str(__u8 mode)
+{
+	if (mode >= ARRAY_SIZE(ovpn_mode_strings) || !ovpn_mode_strings[mode])
+		return "(unknown)";
+
+	return ovpn_mode_strings[mode];
+}
+
+static void print_explain(FILE *f)
+{
+	fprintf(f,
+		"Usage: ... ovpn [ mode { p2p | mp } ]\n"
+		"\n"
+		"MODE := p2p | mp\n"
+		"(p2p is the default if mode is not specified)\n");
+}
+
+static int ovpn_parse_opt(struct link_util *lu, int argc, char **argv,
+			  struct nlmsghdr *n)
+{
+	while (argc > 0) {
+		if (strcmp(*argv, "mode") == 0) {
+			int mode, err;
+
+			NEXT_ARG();
+			mode = parse_one_of("mode", *argv, ovpn_mode_strings,
+					    ARRAY_SIZE(ovpn_mode_strings),
+					    &err);
+			if (err)
+				return err;
+			addattr8(n, 1024, IFLA_OVPN_MODE, mode);
+		} else if (strcmp(*argv, "help") == 0) {
+			print_explain(stderr);
+			return -1;
+		} else {
+			fprintf(stderr, "ovpn: unknown option \"%s\"?\n", *argv);
+			print_explain(stderr);
+			return -1;
+		}
+		argc--;
+		argv++;
+	}
+
+	return 0;
+}
+
+static void ovpn_print_opt(struct link_util *lu, FILE *f, struct rtattr *tb[])
+{
+	__u8 mode;
+
+	if (!tb || !tb[IFLA_OVPN_MODE] ||
+	    RTA_PAYLOAD(tb[IFLA_OVPN_MODE]) < sizeof(mode))
+		return;
+
+	mode = rta_getattr_u8(tb[IFLA_OVPN_MODE]);
+
+	print_string(PRINT_ANY, "mode", "mode %s ", ovpn_mode_to_str(mode));
+}
+
+static void ovpn_print_help(struct link_util *lu, int argc, char **argv,
+			    FILE *f)
+{
+	print_explain(f);
+}
+
+struct link_util ovpn_link_util = {
+	.id		= "ovpn",
+	.maxattr	= IFLA_OVPN_MAX,
+	.parse_opt	= ovpn_parse_opt,
+	.print_opt	= ovpn_print_opt,
+	.print_help	= ovpn_print_help,
+};
diff --git a/man/man8/ip-link.8.in b/man/man8/ip-link.8.in
index fc7f0248..d54d2fbc 100644
--- a/man/man8/ip-link.8.in
+++ b/man/man8/ip-link.8.in
@@ -287,6 +287,7 @@ ip-link \- network device configuration
 .BR netdevsim " |"
 .BR netkit " |"
 .BR nlmon " |"
+.BR ovpn " |"
 .BR pfcp " |"
 .BR rmnet " |"
 .BR sit " |"
@@ -430,6 +431,9 @@ Link types:
 .BR nlmon
 - Netlink monitoring device
 .sp
+.BR ovpn
+- OpenVPN Data Channel Offload device
+.sp
 .BR pfcp
 - Packet Forwarding Control Protocol device
 .sp
@@ -1349,6 +1353,26 @@ the following additional arguments are supported:
 .BI  mode " MODE "
 - specifies the mode (datagram or connected) to use.
 
+.TP
+OVPN Type Support
+For a link of type
+.I OVPN
+the following additional arguments are supported:
+
+.BI "ip link add " DEVICE
+.BR "type ovpn " [ " mode " "{ " p2p " | " mp " }" " ]"
+
+.in +8
+.sp
+.BR mode " { " p2p " | " mp " }"
+- selects the OpenVPN device mode. The default,
+.BR p2p ,
+creates a point-to-point device for a single peer. The
+.B mp
+mode creates a multi-peer device.
+
+.in -8
+
 .TP
 ERSPAN Type Support
 For a link of type
-- 
2.43.0