[RFC PATCH iproute2-next v4] iplink: bridge: Add sup20230919-fdb_limit-v4-0-1a2a59694d67@avm.der bridge FDB learning limits

[Johannes Nixdorf <jnixdorf-oss@avm.de>]

Support setting the FDB limit through ip link. The arguments is:
 - fdb_max_learned: A 32-bit unsigned integer specifying the maximum
                    number of learned FDB entries, with 0 disabling
                    the limit.

Also support reading back the current number of learned FDB entries in
the bridge by this count. The returned value's name is:
 - fdb_n_learned: A 32-bit unsigned integer specifying the current number
                  of learned FDB entries.

Example:

 # ip -d -j -p link show br0
[ {
...
        "linkinfo": {
            "info_kind": "bridge",
            "info_data": {
...
                "fdb_n_learned": 2,
                "fdb_max_learned": 0,
...
            }
        },
...
    } ]
 # ip link set br0 type bridge fdb_max_learned 1024
 # ip -d -j -p link show br0
[ {
...
        "linkinfo": {
            "info_kind": "bridge",
            "info_data": {
...
                "fdb_n_learned": 2,
                "fdb_max_learned": 1024,
...
            }
        },
...
    } ]

Signed-off-by: Johannes Nixdorf <jnixdorf-oss@avm.de>
---
I will resend this mail as non-rfc after the kernel UAPI changes landed.

Link to the kernel changes: https://lore.kernel.org/netdev/20230919-fdb_limit-v4-0-39f0293807b8@avm.de/
---
Changes in v4:
 - Removed _entries from the names. (from review)
 - Removed the UAPI change, to be synced from linux separately by the
   maintainer. (from review)
   For local testing e.g. `make CCOPTS="-O2 -pipe
   -I${path_to_dev_kernel_headers}"` works as a workaround.
 - Downgraded to an RFC until the kernel changes land.
 - Link to v3: https://lore.kernel.org/netdev/20230905-fdb_limit-v3-1-34bb124556d8@avm.de/

Changes in v3:
 - Properly split the net-next and iproute2-next threads. (from review)
 - Changed to *_n_* instead of *_cur_*. (from review)
 - Use strcmp() instead of matches(). (from review)
 - Made names in code and documentation consistent. (from review)
 - Various documentation fixes. (from review)
 - Link to v2: https://lore.kernel.org/netdev/20230619071444.14625-1-jnixdorf-oss@avm.de/

Changes in v2:
 - Sent out the first corresponding iproute2 patches.
 - Link to v1: https://lore.kernel.org/netdev/20230515085046.4457-1-jnixdorf-oss@avm.de/
---
 ip/iplink_bridge.c    | 21 +++++++++++++++++++++
 man/man8/ip-link.8.in | 10 ++++++++++
 2 files changed, 31 insertions(+)

diff --git a/ip/iplink_bridge.c b/ip/iplink_bridge.c
index 462075295308..6b70ffbb6f5f 100644
--- a/ip/iplink_bridge.c
+++ b/ip/iplink_bridge.c
@@ -34,6 +34,7 @@ static void print_explain(FILE *f)
 		"		  [ group_fwd_mask MASK ]\n"
 		"		  [ group_address ADDRESS ]\n"
 		"		  [ no_linklocal_learn NO_LINKLOCAL_LEARN ]\n"
+		"		  [ fdb_max_learned FDB_MAX_LEARNED ]\n"
 		"		  [ vlan_filtering VLAN_FILTERING ]\n"
 		"		  [ vlan_protocol VLAN_PROTOCOL ]\n"
 		"		  [ vlan_default_pvid VLAN_DEFAULT_PVID ]\n"
@@ -168,6 +169,14 @@ static int bridge_parse_opt(struct link_util *lu, int argc, char **argv,
 				bm.optval |= no_ll_learn_bit;
 			else
 				bm.optval &= ~no_ll_learn_bit;
+		} else if (strcmp(*argv, "fdb_max_learned") == 0) {
+			__u32 fdb_max_learned;
+
+			NEXT_ARG();
+			if (get_u32(&fdb_max_learned, *argv, 0))
+				invarg("invalid fdb_max_learned", *argv);
+
+			addattr32(n, 1024, IFLA_BR_FDB_MAX_LEARNED, fdb_max_learned);
 		} else if (matches(*argv, "fdb_flush") == 0) {
 			addattr(n, 1024, IFLA_BR_FDB_FLUSH);
 		} else if (matches(*argv, "vlan_default_pvid") == 0) {
@@ -544,6 +553,18 @@ static void bridge_print_opt(struct link_util *lu, FILE *f, struct rtattr *tb[])
 	if (tb[IFLA_BR_GC_TIMER])
 		_bridge_print_timer(f, "gc_timer", tb[IFLA_BR_GC_TIMER]);
 
+	if (tb[IFLA_BR_FDB_N_LEARNED])
+		print_uint(PRINT_ANY,
+			   "fdb_n_learned",
+			   "fdb_n_learned %u ",
+			   rta_getattr_u32(tb[IFLA_BR_FDB_N_LEARNED]));
+
+	if (tb[IFLA_BR_FDB_MAX_LEARNED])
+		print_uint(PRINT_ANY,
+			   "fdb_max_learned",
+			   "fdb_max_learned %u ",
+			   rta_getattr_u32(tb[IFLA_BR_FDB_MAX_LEARNED]));
+
 	if (tb[IFLA_BR_VLAN_DEFAULT_PVID])
 		print_uint(PRINT_ANY,
 			   "vlan_default_pvid",
diff --git a/man/man8/ip-link.8.in b/man/man8/ip-link.8.in
index 7365d0c6b14f..e82b2dbb0070 100644
--- a/man/man8/ip-link.8.in
+++ b/man/man8/ip-link.8.in
@@ -1630,6 +1630,8 @@ the following additional arguments are supported:
 ] [
 .BI no_linklocal_learn " NO_LINKLOCAL_LEARN "
 ] [
+.BI fdb_max_learned " FDB_MAX_LEARNED "
+] [
 .BI vlan_filtering " VLAN_FILTERING "
 ] [
 .BI vlan_protocol " VLAN_PROTOCOL "
@@ -1741,6 +1743,14 @@ or off
 When disabled, the bridge will not learn from link-local frames (default:
 enabled).
 
+.BI fdb_max_learned " FDB_MAX_LEARNED "
+- set the maximum number of learned FDB entries. If
+.RI ( FDB_MAX_LEARNED " == 0) "
+the feature is disabled. Default is
+.BR 0 .
+.I FDB_MAX_LEARNED
+is a 32bit unsigned integer.
+
 .BI vlan_filtering " VLAN_FILTERING "
 - turn VLAN filtering on
 .RI ( VLAN_FILTERING " > 0) "

---
base-commit: c31fd80a2268c0b1b77e1d65827003a2327315b8
change-id: 20230905-fdb_limit-ace1467c6a84

Best regards,
-- 
Johannes Nixdorf <jnixdorf-oss@avm.de>