[PATCH net-next v2 1/3] selftests: drv-net: resolve remote interface name

[Jakub Kicinski <kuba@kernel.org>]

Find out and record in env the name of the interface which remote host
will use for the IP address provided via config.

Interface name is useful for mausezahn and for setting up tunnels.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
v2:
 - check for IP being on multiple ifcs
v1: https://lore.kernel.org/20250213003454.1333711-2-kuba@kernel.org
---
 tools/testing/selftests/drivers/net/lib/py/env.py | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tools/testing/selftests/drivers/net/lib/py/env.py b/tools/testing/selftests/drivers/net/lib/py/env.py
index 886b4904613c..55d6b3d992b6 100644
--- a/tools/testing/selftests/drivers/net/lib/py/env.py
+++ b/tools/testing/selftests/drivers/net/lib/py/env.py
@@ -154,6 +154,9 @@ from .remote import Remote
         self.ifname = self.dev['ifname']
         self.ifindex = self.dev['ifindex']
 
+        # resolve remote interface name
+        self.remote_ifname = self.resolve_remote_ifc()
+
         self._required_cmd = {}
 
     def create_local(self):
@@ -200,6 +203,18 @@ from .remote import Remote
             raise Exception("Invalid environment, missing configuration:", missing,
                             "Please see tools/testing/selftests/drivers/net/README.rst")
 
+    def resolve_remote_ifc(self):
+        v4 = v6 = None
+        if self.remote_v4:
+            v4 = ip("addr show to " + self.remote_v4, json=True, host=self.remote)
+        if self.remote_v6:
+            v6 = ip("addr show to " + self.remote_v6, json=True, host=self.remote)
+        if v4 and v6 and v4[0]["ifname"] != v6[0]["ifname"]:
+            raise Exception("Can't resolve remote interface name, v4 and v6 don't match")
+        if (v4 and len(v4) > 1) or (v6 and len(v6) > 1):
+            raise Exception("Can't resolve remote interface name, multiple interfaces match")
+        return v6[0]["ifname"] if v6 else v4[0]["ifname"]
+
     def __enter__(self):
         return self
 
-- 
2.48.1