netdev - Re: [PATCH] ppp: Add rtnl attribute IFLA_PPP_UNIT

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Message-ID: <20220709120906.ymkhn5diywadgrka@pali>
Date:   Sat, 9 Jul 2022 14:09:06 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Guillaume Nault <gnault@...hat.com>
Cc:     James Carlson <carlsonj@...kingcode.com>,
        Chris Fowler <cfowler@...postsentinel.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paul Mackerras <paulus@...ba.org>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-ppp@...r.kernel.org" <linux-ppp@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ppp: Add rtnl attribute IFLA_PPP_UNIT_ID for specifying
 ppp unit id

On Tuesday 17 August 2021 18:21:55 Pali Rohár wrote:
> On Tuesday 17 August 2021 18:05:25 Guillaume Nault wrote:
> > On Mon, Aug 16, 2021 at 06:23:55PM +0200, Pali Rohár wrote:
> > > On Monday 16 August 2021 18:11:14 Guillaume Nault wrote:
> > > > Do you have plans for adding netlink support to pppd? If so, is the
> > > > project ready to accept such code?
> > > 
> > > Yes, I have already some WIP code and I'm planning to send a pull
> > > request to pppd on github for it. I guess that it could be accepted,
> > 
> > I guess you can easily use the netlink api for cases where the "unit"
> > option isn't specified and fall back to the ioctl api when it is. If
> > all goes well, then we can extend the netlink api to accept a unit id.
> > 
> > But what about the lack of netlink feedback about the created
> > interface? Are you restricted to use netlink only when the "ifname"
> > option is provided?
> 
> Exactly, this is how I wrote my WIP code...

Sorry for a long delay (I forgot about it). Now I created pull request
for pppd https://github.com/ppp-project/ppp/pull/354 which adds support
for creating ppp interface via rtnetlink. rtnetlink is used only when
ppp unit id was not provided and interface name was provided.

> > > specially if there still would be backward compatibility via ioctl for
> > > kernels which do not support rtnl API.
> > 
> > Indeed, I'd expect keeping compatiblitity with old kernels that only
> > have the ioctl api to be a must (but I have no experience contributing
> > to the pppd project).
> > 
> > > One of the argument which can be
> > > used why rtnl API is better, is fixing issue: atomic creating of
> > > interface with specific name.
> > 
> > Yes, that looks useful.
> >