[RFC net-next 4/6] selftests: net: add tx_extra_headroom test

[David Keogh <dkeogh@amazon.com>]

Exercise the IFLA_TX_EXTRA_HEADROOM attribute through YNL: the default
of zero, setting values up to the maximum and back to zero, rejection
of a value above the maximum, supplying the attribute at link creation,
the change notification, persistence across link down/up and across a
network namespace move, and that a VLAN created on top of a configured
device does not inherit the setting.

Signed-off-by: David Keogh <dkeogh@amazon.com>
---
 tools/testing/selftests/net/Makefile          |   1 +
 .../selftests/net/tx_extra_headroom.py        | 137 ++++++++++++++++++
 2 files changed, 138 insertions(+)
 create mode 100755 tools/testing/selftests/net/tx_extra_headroom.py

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 54beea2e3..0eb9a69e9 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -120,6 +120,7 @@ TEST_PROGS := \
 	test_vxlan_vnifiltering.sh \
 	tfo_passive.sh \
 	traceroute.sh \
+	tx_extra_headroom.py \
 	txtimestamp.sh \
 	udpgro.sh \
 	udpgro_bench.sh \
diff --git a/tools/testing/selftests/net/tx_extra_headroom.py b/tools/testing/selftests/net/tx_extra_headroom.py
new file mode 100755
index 000000000..f6f087e98
--- /dev/null
+++ b/tools/testing/selftests/net/tx_extra_headroom.py
@@ -0,0 +1,137 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+"""Tests for the IFLA_TX_EXTRA_HEADROOM link attribute."""
+
+from lib.py import ksft_run, ksft_exit, ksft_eq, ksft_raises, ksft_true
+from lib.py import ip
+from lib.py import NetNS, NetNSEnter
+from lib.py import Netlink, NlError, RtnlFamily
+
+ATTR = "tx-extra-headroom"
+MAX = 512
+
+
+def ifindex(name):
+    return ip(f"link show dev {name}", json=True)[0]["ifindex"]
+
+
+def get(rtnl, idx):
+    return rtnl.getlink({"ifi-index": idx})[ATTR]
+
+
+def set_(rtnl, idx, val):
+    rtnl.setlink({"ifi-index": idx, ATTR: val})
+
+
+def test_default_and_set() -> None:
+    """Default is 0, values up to the maximum are accepted, 0 resets."""
+    with NetNS() as ns, NetNSEnter(str(ns)):
+        ip("link add d0 type dummy")
+        rtnl = RtnlFamily()
+        idx = ifindex("d0")
+
+        ksft_eq(get(rtnl, idx), 0)
+        for val in (1, 256, MAX):
+            set_(rtnl, idx, val)
+            ksft_eq(get(rtnl, idx), val)
+        set_(rtnl, idx, 0)
+        ksft_eq(get(rtnl, idx), 0)
+
+
+def test_reject_above_max() -> None:
+    """Values above the maximum are rejected by the policy."""
+    with NetNS() as ns, NetNSEnter(str(ns)):
+        ip("link add d0 type dummy")
+        rtnl = RtnlFamily()
+        idx = ifindex("d0")
+
+        set_(rtnl, idx, 128)
+        with ksft_raises(NlError):
+            set_(rtnl, idx, MAX + 1)
+        ksft_eq(get(rtnl, idx), 128)
+
+
+def test_newlink() -> None:
+    """The attribute can be supplied when the link is created."""
+    with NetNS() as ns, NetNSEnter(str(ns)):
+        rtnl = RtnlFamily()
+        rtnl.newlink({"ifname": "d0", "linkinfo": {"kind": "dummy"},
+                      ATTR: 64},
+                     flags=[Netlink.NLM_F_CREATE, Netlink.NLM_F_EXCL])
+        ksft_eq(get(rtnl, ifindex("d0")), 64)
+
+
+def test_notification() -> None:
+    """A change produces a link notification carrying the new value."""
+    with NetNS() as ns, NetNSEnter(str(ns)):
+        ip("link add d0 type dummy")
+        ip("link set dev d0 up")
+        rtnl = RtnlFamily()
+        idx = ifindex("d0")
+
+        rtnl.ntf_subscribe("rtnlgrp-link")
+        set_(rtnl, idx, 192)
+
+        seen = None
+        for msg in rtnl.poll_ntf(duration=1):
+            if msg["name"] == "getlink" and msg["msg"]["ifi-index"] == idx:
+                seen = msg["msg"][ATTR]
+                break
+        ksft_eq(seen, 192)
+
+
+def test_survives_down_up() -> None:
+    """Toggling the link does not reset the value."""
+    with NetNS() as ns, NetNSEnter(str(ns)):
+        ip("link add d0 type dummy")
+        rtnl = RtnlFamily()
+        idx = ifindex("d0")
+
+        set_(rtnl, idx, 96)
+        ip("link set dev d0 up")
+        ksft_eq(get(rtnl, idx), 96)
+        ip("link set dev d0 down")
+        ksft_eq(get(rtnl, idx), 96)
+
+
+def test_survives_netns_move() -> None:
+    """Moving the link to another namespace keeps the value."""
+    with NetNS() as ns1, NetNS() as ns2:
+        with NetNSEnter(str(ns1)):
+            ip("link add d0 type dummy")
+            rtnl = RtnlFamily()
+            set_(rtnl, ifindex("d0"), 160)
+            ip(f"link set dev d0 netns {ns2}")
+
+        with NetNSEnter(str(ns2)):
+            rtnl = RtnlFamily()
+            ksft_eq(get(rtnl, ifindex("d0")), 160)
+
+
+def test_not_inherited() -> None:
+    """Stacked devices do not inherit the value of the device below."""
+    with NetNS() as ns, NetNSEnter(str(ns)):
+        ip("link add d0 type dummy")
+        rtnl = RtnlFamily()
+        set_(rtnl, ifindex("d0"), 224)
+
+        ip("link add link d0 name d0.10 type vlan id 10")
+        ksft_eq(get(rtnl, ifindex("d0.10")), 0)
+        ksft_true(rtnl.getlink({"ifi-index": ifindex("d0.10")})["headroom"]
+                  >= 4, "vlan needed_headroom")
+
+
+def main() -> None:
+    ksft_run([test_default_and_set,
+              test_reject_above_max,
+              test_newlink,
+              test_notification,
+              test_survives_down_up,
+              test_survives_netns_move,
+              test_not_inherited])
+    ksft_exit()
+
+
+if __name__ == "__main__":
+    main()
-- 
2.50.1