linux-kernel - Re: [PATCH] drivers/net/wan/lapbether: Use needed_headroom instead of hard_header

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Message-ID: <CA+ASDXPRLqq=vxnkF4z8=xvuqOKuuoqifvsNsERWg9uYJrFXgg@mail.gmail.com>
Date:   Thu, 30 Jul 2020 17:24:27 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Xie He <xie.he.0141@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux X25 <linux-x25@...r.kernel.org>,
        Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: [PATCH] drivers/net/wan/lapbether: Use needed_headroom instead of hard_header_len

On Tue, Jul 28, 2020 at 6:42 PM Xie He <xie.he.0141@...il.com> wrote:
> On Tue, Jul 28, 2020 at 12:52 PM -0700
> Brian Norris <briannorris@...omium.org> wrote:
> > What is the intention with this X25 protocol? I guess the headers added
> > in lapbeth_data_transmit() are supposed to be "invisible", as with this
> > note in af_packet.c?
...
> This driver is not intended to be used with IPv4 or IPv6 protocols,
> but is intended to be used with a special "X.25" protocol. That's the
> reason the device type is ARPHRD_X25. I used "grep" in the X.25
> network layer code (net/x25) and I found there's nowhere
> "dev_hard_header" is called. I also used "grep" in all the X.25

That well could just be a bug in net/x25/. But from context, it does
appear that X.25 does not intend to expose its headers to higher
layers.

> drivers in the kernel (lapbether.c, x25_asy.c, hdlc_x25.c under
> drivers/net/wan) and I found no driver implemented "header_ops". So I
> think the X.25 networking code doesn't expect any header visible
> outside of the device driver, and X.25 drivers should make their
> headers invisible outside of them.
>
> So I think hard_header_len should be 0 for all X.25 drivers, so that
> they can be used correctly with af_packet.c.
>
> I don't know if this sounds plausible to you. If it does, could you
> please let me have your name in a "Reviewed_by" tag. It would be of
> great help to have your support. Thanks!

Sure, I can do that:

Reviewed-by: Brian Norris <briannorris@...omium.org>

I guess x25 is basically an abandoned project, if you're coming to me for this?