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From:   Xie He <xie.he.0141@gmail.com>
Date:   Wed, 18 Nov 2020 05:46:54 -0800
Message-ID: <CAJht_EMd5iKmdvePgYzWYXnG=5LxQopStzz_Lk9uNSkRyrudqw@mail.gmail.com>
Subject: Re: [PATCH net-next v2 5/6] net/lapb: support netdev events
To:     Martin Schiller <ms@dev.tdt.de>
Cc:     Andrew Hendry <andrew.hendry@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Linux X25 <linux-x25@vger.kernel.org>,
        Linux Kernel Network Developers <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, Nov 18, 2020 at 5:03 AM Xie He <xie.he.0141@gmail.com> wrote:
>
> On Wed, Nov 18, 2020 at 12:49 AM Martin Schiller <ms@dev.tdt.de> wrote:
> >
> > I also have a patch here that implements an "on demand" link feature,
> > which we used for ISDN dialing connections.
> > As ISDN is de facto dead, this is not relevant anymore. But if we want
> > such kind of feature, I think we need to stay with the method to control
> > L2 link state from L3.
>
> I see. Hmm...
>
> I guess for ISDN, the current code (before this patch series) is the
> best. We only establish the connection when L3 has packets to send.
>
> Can we do this? We let L2 handle all device-up / device-down /
> carrier-up / carrier-down events. And when L3 has some packets to send
> but it still finds the L2 link is not up, it will then instruct L2 to
> connect.
>
> This way we may be able to both keep the logic simple and still keep
> L3 compatible with ISDN.

Another solution might be letting ISDN automatically connect when it
receives the first packet from L3. This way we can still free L3 from
all handlings of L2 connections.