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

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Message-ID: <87o6z5di4m.fsf@nvidia.com>
Date: Thu, 13 Feb 2025 15:31:57 +0100
From: Petr Machata <petrm@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: <davem@...emloft.net>, <netdev@...r.kernel.org>, <edumazet@...gle.com>,
	<pabeni@...hat.com>, <andrew+netdev@...n.ch>, <horms@...nel.org>,
	<willemb@...gle.com>, <shuah@...nel.org>, <petrm@...dia.com>
Subject: Re: [PATCH net-next 1/3] selftests: drv-net: resolve remote
 interface name


Jakub Kicinski <kuba@...nel.org> writes:

> 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@...nel.org>
> ---
>  tools/testing/selftests/drivers/net/lib/py/env.py | 13 +++++++++++++
>  1 file changed, 13 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..fc649797230b 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 +203,16 @@ 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")
> +        return v6[0]["ifname"] if v6 else v4[0]["ifname"]

Is existence of more than one interface with the same IP address a
concern? I guess such configuration is broken and wouldn't come up in a
selftest, but consider throwing in an "len(v4) == len(v6) == 1" for
robustness sake. I guess it could in fact replace the "v4 and v6" bit.

> +
>      def __enter__(self):
>          return self