netdev - [PATCH iproute2 -next v2 2/3] ip, neigh: Add missing NTF

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Date:   Mon, 25 Oct 2021 17:47:27 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     dsahern@...nel.org
Cc:     netdev@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH iproute2 -next v2 2/3] ip, neigh: Add missing NTF_USE support

Currently, ip neigh does not support the NTF_USE flag. Similar to other flags
such as extern_learn, add cmdline support. The flag dump support is explicitly
missing here, since the kernel does not propagate the flag back to user space.

Usage example:

  # ./ip/ip n replace 192.168.178.30 dev enp5s0 use extern_learn
  # ./ip/ip n
  192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a extern_learn REACHABLE
  [...]

Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
---
 ip/ipneigh.c            | 4 +++-
 man/man8/ip-neighbour.8 | 8 ++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/ip/ipneigh.c b/ip/ipneigh.c
index a8006f94..874c9033 100644
--- a/ip/ipneigh.c
+++ b/ip/ipneigh.c
@@ -51,7 +51,7 @@ static void usage(void)
 	fprintf(stderr,
 		"Usage: ip neigh { add | del | change | replace }\n"
 		"                { ADDR [ lladdr LLADDR ] [ nud STATE ] proxy ADDR }\n"
-		"                [ dev DEV ] [ router ] [ extern_learn ] [ protocol PROTO ]\n"
+		"                [ dev DEV ] [ router ] [ use ] [ extern_learn ] [ protocol PROTO ]\n"
 		"\n"
 		"	ip neigh { show | flush } [ proxy ] [ to PREFIX ] [ dev DEV ] [ nud STATE ]\n"
 		"				  [ vrf NAME ] [ nomaster ]\n"
@@ -148,6 +148,8 @@ static int ipneigh_modify(int cmd, int flags, int argc, char **argv)
 			req.ndm.ndm_flags |= NTF_PROXY;
 		} else if (strcmp(*argv, "router") == 0) {
 			req.ndm.ndm_flags |= NTF_ROUTER;
+		} else if (strcmp(*argv, "use") == 0) {
+			req.ndm.ndm_flags |= NTF_USE;
 		} else if (matches(*argv, "extern_learn") == 0) {
 			req.ndm.ndm_flags |= NTF_EXT_LEARNED;
 		} else if (strcmp(*argv, "dev") == 0) {
diff --git a/man/man8/ip-neighbour.8 b/man/man8/ip-neighbour.8
index 02862964..3001cd01 100644
--- a/man/man8/ip-neighbour.8
+++ b/man/man8/ip-neighbour.8
@@ -25,6 +25,7 @@ ip-neighbour \- neighbour/arp tables management.
 .B  dev
 .IR DEV " ] [ "
 .BR router " ] [ "
+.BR use " ] [ "
 .BR extern_learn " ]"
 
 .ti -8
@@ -92,6 +93,13 @@ indicates whether we are proxying for this neighbour entry
 .BI router
 indicates whether neighbour is a router
 
+.TP
+.BI use
+this neigh entry is in "use". This option can be used to indicate to
+the kernel that a controller is using this dynamic entry. If the entry
+does not exist, the kernel will resolve it. If it exists, an attempt
+to refresh the neighbor entry will be triggered.
+
 .TP
 .BI extern_learn
 this neigh entry was learned externally. This option can be used to
-- 
2.27.0