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From: "Pali Rohár" <pali@kernel.org>
To: Guillaume Nault <gnault@redhat.com>
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 12:58:25 +0200	[thread overview]
Message-ID: <20210802105825.td57b5rd3d6xfxfo@pali> (raw)
In-Reply-To: <20210802100238.GA3756@pc-32.home>

On Monday 02 August 2021 12:02:38 Guillaume Nault wrote:
> 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()).

I see...

> 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()).

Do you know if there is some workaround / other solution which can be
used by userspace applications now? And also with stable kernels (which
obviously do not receive this new NLM_F_ECHO support for RTM_NEWLINK)?

  reply	other threads:[~2021-08-02 10:58 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
2021-08-02 10:58   ` Pali Rohár [this message]
2021-08-02 13:43     ` Guillaume Nault
2021-08-02 17:23       ` Pali Rohár

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