[PATCH iproute2-next 2/2] bridge: fdb: enable FDB blackhole feature

[Hans Schultz <netdev@xxxxxxxxxxxxxxxxxxxx>]

Block traffic to a specific host with the command:
bridge fdb add <MAC> vlan <vid> dev br0 blackhole

The blackhole FDB entries can be added, deleted and replaced with
ordinary FDB entries.

Signed-off-by: Hans Schultz <netdev@xxxxxxxxxxxxxxxxxxxx>
---
 bridge/fdb.c                   | 7 ++++++-
 include/uapi/linux/neighbour.h | 4 ++++
 man/man8/bridge.8              | 6 ++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/bridge/fdb.c b/bridge/fdb.c
index 0fbe9bd3..2160f1c2 100644
--- a/bridge/fdb.c
+++ b/bridge/fdb.c
@@ -38,7 +38,7 @@ static void usage(void)
 	fprintf(stderr,
 		"Usage: bridge fdb { add | append | del | replace } ADDR dev DEV\n"
 		"              [ self ] [ master ] [ use ] [ router ] [ extern_learn ]\n"
-		"              [ sticky ] [ local | static | dynamic ] [ vlan VID ]\n"
+		"              [ sticky ] [ local | static | dynamic ] [blackhole] [ vlan VID ]\n"
 		"              { [ dst IPADDR ] [ port PORT] [ vni VNI ] | [ nhid NHID ] }\n"
 		"	       [ via DEV ] [ src_vni VNI ]\n"
 		"       bridge fdb [ show [ br BRDEV ] [ brport DEV ] [ vlan VID ]\n"
@@ -116,6 +116,9 @@ static void fdb_print_flags(FILE *fp, unsigned int flags, __u8 ext_flags)
 	if (flags & NTF_STICKY)
 		print_string(PRINT_ANY, NULL, "%s ", "sticky");
 
+	if (ext_flags & NTF_EXT_BLACKHOLE)
+		print_string(PRINT_ANY, NULL, "%s ", "blackhole");
+
 	if (ext_flags & NTF_EXT_LOCKED)
 		print_string(PRINT_ANY, NULL, "%s ", "locked");
 
@@ -493,6 +496,8 @@ static int fdb_modify(int cmd, int flags, int argc, char **argv)
 			req.ndm.ndm_flags |= NTF_EXT_LEARNED;
 		} else if (matches(*argv, "sticky") == 0) {
 			req.ndm.ndm_flags |= NTF_STICKY;
+		} else if (matches(*argv, "blackhole") == 0) {
+			ext_flags |= NTF_EXT_BLACKHOLE;
 		} else {
 			if (strcmp(*argv, "to") == 0)
 				NEXT_ARG();
diff --git a/include/uapi/linux/neighbour.h b/include/uapi/linux/neighbour.h
index 4dda051b..cc7d540e 100644
--- a/include/uapi/linux/neighbour.h
+++ b/include/uapi/linux/neighbour.h
@@ -54,6 +54,7 @@ enum {
 /* Extended flags under NDA_FLAGS_EXT: */
 #define NTF_EXT_MANAGED		(1 << 0)
 #define NTF_EXT_LOCKED		(1 << 1)
+#define NTF_EXT_BLACKHOLE	(1 << 2)
 
 /*
  *	Neighbor Cache Entry States.
@@ -91,6 +92,9 @@ enum {
  * NTF_EXT_LOCKED flagged FDB entries are placeholder entries used with the
  * locked port feature, that ensures that an entry exists while at the same
  * time dropping packets on ingress with src MAC and VID matching the entry.
+ *
+ * NTF_EXT_BLACKHOLE flagged FDB entries ensure that no forwarding is allowed
+ * from any port to the destination MAC, VID pair associated with it.
  */
 
 struct nda_cacheinfo {
diff --git a/man/man8/bridge.8 b/man/man8/bridge.8
index 40250477..af2e7db2 100644
--- a/man/man8/bridge.8
+++ b/man/man8/bridge.8
@@ -699,6 +699,12 @@ controller learnt dynamic entry. Kernel will not age such an entry.
 - this entry will not change its port due to learning.
 .sp
 
+.B blackhole
+- this is an entry that denies all forwarding from any port to a destination
+matching the entry. It can be added by userspace, but the flag is mostly set
+from a hardware driver.
+.sp
+
 .in -8
 The next command line parameters apply only
 when the specified device
-- 
2.34.1