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From: Guillaume Nault <gnault@redhat.com>
To: "Pali Rohár" <pali@kernel.org>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: How to find out name or id of newly created interface
Date: Mon, 2 Aug 2021 12:02:38 +0200	[thread overview]
Message-ID: <20210802100238.GA3756@pc-32.home> (raw)
In-Reply-To: <20210731203054.72mw3rbgcjuqbf4j@pali>

On Sat, Jul 31, 2021 at 10:30:54PM +0200, Pali Rohár wrote:
> 
> And now I would like to know, how to race-free find out interface name
> (or id) of this newly created interface?
> 
> Response to RTM_NEWLINK/NLM_F_CREATE packet from kernel contains only
> buffer with struct nlmsgerr where is just error number (zero for
> success) without any additional information.

You'd normally pass the NLM_F_ECHO flag on the netlink request, so the
kernel would echo back a netlink message with all information about the
device it created.

Unfortunately, many netlink handlers don't implement this feature. And
it seems that RTM_NEWLINK is part of them (rtmsg_ifinfo_send() doesn't
provide the 'nlh' argument when it calls rtnl_notify()).

So the proper solution is to implement NLM_F_ECHO support for
RTM_NEWLINK messages (RTM_NEWROUTE is an example of netlink handler
that supports NLM_F_ECHO, see rtmsg_fib()).


  parent reply	other threads:[~2021-08-02 10:02 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-31 20:30 Pali Rohár
2021-08-01 14:31 ` Andrew Lunn
2021-08-01 14:38   ` Pali Rohár
2021-08-02 14:21     ` Andrew Lunn
2021-08-02 17:25       ` Pali Rohár
2021-08-02 10:02 ` Guillaume Nault [this message]
2021-08-02 10:58   ` Pali Rohár
2021-08-02 13:43     ` Guillaume Nault
2021-08-02 17:23       ` Pali Rohár

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