[PATCH net-next 08/11] selftests: drv-net: Add MAC loopback netdevsim test

["Björn Töpel" <bjorn@kernel.org>]

Add loopback_nsim.py with netdevsim-specific tests for MAC
loopback via the new ethtool_ops loopback callbacks:

 - test_get_mac_entry: verify MAC entry appears in dump with correct
   component, name, and supported directions
 - test_set_mac_near_end: SET near-end, verify via GET and debugfs
 - test_set_mac_disable: enable then disable
 - test_set_mac_unknown_name: SET with wrong name, expect EOPNOTSUPP

Signed-off-by: Björn Töpel <bjorn@kernel.org>
---
 .../testing/selftests/drivers/net/hw/Makefile |   1 +
 .../selftests/drivers/net/hw/loopback_nsim.py | 135 ++++++++++++++++++
 2 files changed, 136 insertions(+)
 create mode 100755 tools/testing/selftests/drivers/net/hw/loopback_nsim.py

diff --git a/tools/testing/selftests/drivers/net/hw/Makefile b/tools/testing/selftests/drivers/net/hw/Makefile
index 1c341aaa88c6..d7041b9d7461 100644
--- a/tools/testing/selftests/drivers/net/hw/Makefile
+++ b/tools/testing/selftests/drivers/net/hw/Makefile
@@ -32,6 +32,7 @@ TEST_PROGS = \
 	irq.py \
 	loopback.sh \
 	loopback_drv.py \
+	loopback_nsim.py \
 	nic_timestamp.py \
 	nk_netns.py \
 	pp_alloc_fail.py \
diff --git a/tools/testing/selftests/drivers/net/hw/loopback_nsim.py b/tools/testing/selftests/drivers/net/hw/loopback_nsim.py
new file mode 100755
index 000000000000..5edc999d920b
--- /dev/null
+++ b/tools/testing/selftests/drivers/net/hw/loopback_nsim.py
@@ -0,0 +1,135 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+"""Netdevsim-specific tests for MAC loopback via ethtool_ops.
+
+Verifies that MAC loopback entries appear in dumps, that SET
+operations update state correctly (both via GET and debugfs).
+"""
+
+import errno
+import os
+
+from lib.py import ksft_run, ksft_exit, ksft_eq
+from lib.py import KsftSkipEx, KsftFailEx, ksft_disruptive
+from lib.py import EthtoolFamily, NlError
+from lib.py import NetDrvEnv, ip, defer
+
+# Direction flags as YNL returns them
+DIR_NONE = set()
+DIR_NEAR_END = {'near-end'}
+DIR_FAR_END = {'far-end'}
+
+
+def _nsim_dfs_path(cfg):
+    return cfg._ns.nsims[0].dfs_dir
+
+
+def _dfs_read_u32(cfg, path):
+    with open(os.path.join(_nsim_dfs_path(cfg), path)) as f:
+        return int(f.read().strip())
+
+
+def _dfs_write_u32(cfg, path, val):
+    with open(os.path.join(_nsim_dfs_path(cfg), path), "w") as f:
+        f.write(str(val))
+
+
+def _get_loopback(cfg):
+    results = cfg.ethnl.loopback_get({
+        'header': {'dev-index': cfg.ifindex}
+    }, dump=True)
+    entries = []
+    for msg in results:
+        if 'entry' in msg:
+            entries.extend(msg['entry'])
+    return entries
+
+
+def _set_loopback(cfg, component, name, direction):
+    cfg.ethnl.loopback_set({
+        'header': {'dev-index': cfg.ifindex},
+        'entry': [{
+            'component': component,
+            'name': name,
+            'direction': direction,
+        }]
+    })
+
+
+def test_get_mac_entry(cfg):
+    """GET should return the MAC loopback entry with correct attributes."""
+    entries = _get_loopback(cfg)
+    mac_entries = [e for e in entries if e['component'] == 'mac']
+
+    ksft_eq(len(mac_entries), 1, "Expected 1 MAC loopback entry")
+    ksft_eq(mac_entries[0]['name'], 'mac')
+    ksft_eq(mac_entries[0]['supported'], DIR_NEAR_END | DIR_FAR_END)
+    ksft_eq(mac_entries[0]['direction'], DIR_NONE)
+
+
+@ksft_disruptive
+def test_set_mac_near_end(cfg):
+    """SET MAC near-end and verify via GET and debugfs."""
+    ip(f"link set dev {cfg.ifname} down")
+    defer(ip, f"link set dev {cfg.ifname} up")
+
+    _set_loopback(cfg, 'mac', 'mac', 'near-end')
+    defer(_set_loopback, cfg, 'mac', 'mac', 0)
+
+    entries = _get_loopback(cfg)
+    mac = [e for e in entries if e['component'] == 'mac']
+    ksft_eq(mac[0]['direction'], DIR_NEAR_END)
+
+    dfs_dir = _dfs_read_u32(cfg, "ethtool/mac_lb/direction")
+    ksft_eq(dfs_dir, 1, "debugfs direction should be 1 (NEAR_END)")
+
+
+@ksft_disruptive
+def test_set_mac_disable(cfg):
+    """Enable then disable MAC loopback."""
+    ip(f"link set dev {cfg.ifname} down")
+    defer(ip, f"link set dev {cfg.ifname} up")
+
+    _set_loopback(cfg, 'mac', 'mac', 'near-end')
+    defer(_set_loopback, cfg, 'mac', 'mac', 0)
+
+    _set_loopback(cfg, 'mac', 'mac', 0)
+
+    entries = _get_loopback(cfg)
+    mac = [e for e in entries if e['component'] == 'mac']
+    ksft_eq(mac[0]['direction'], DIR_NONE, "Direction should be off")
+
+    dfs_dir = _dfs_read_u32(cfg, "ethtool/mac_lb/direction")
+    ksft_eq(dfs_dir, 0, "debugfs direction should be 0")
+
+
+@ksft_disruptive
+def test_set_mac_unknown_name(cfg):
+    """SET with unknown name should fail with EOPNOTSUPP."""
+    ip(f"link set dev {cfg.ifname} down")
+    defer(ip, f"link set dev {cfg.ifname} up")
+
+    try:
+        _set_loopback(cfg, 'mac', 'bogus', 'near-end')
+        raise KsftFailEx("Should have rejected unknown name")
+    except NlError as e:
+        ksft_eq(e.error, errno.EOPNOTSUPP,
+                "Expected EOPNOTSUPP for unknown name")
+
+
+def main() -> None:
+    with NetDrvEnv(__file__) as cfg:
+        cfg.ethnl = EthtoolFamily()
+
+        ksft_run([
+            test_get_mac_entry,
+            test_set_mac_near_end,
+            test_set_mac_disable,
+            test_set_mac_unknown_name,
+        ], args=(cfg, ))
+    ksft_exit()
+
+
+if __name__ == "__main__":
+    main()
-- 
2.53.0