linux-kernel - RE: [PATCH net-next] net: x25_asy: Delete the x25

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Message-ID: <f4b59cfa4f6b4cc89bf2f111974bb86e@AcuMS.aculab.com>
Date:   Fri, 6 Nov 2020 09:03:20 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Xie He' <xie.he.0141@...il.com>, Arnd Bergmann <arnd@...nel.org>
CC:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Networking <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Martin Schiller" <ms@....tdt.de>,
        Andrew Hendry <andrew.hendry@...il.com>,
        Linux X25 <linux-x25@...r.kernel.org>
Subject: RE: [PATCH net-next] net: x25_asy: Delete the x25_asy driver

From: Xie He
> Sent: 05 November 2020 22:47
> 
> On Thu, Nov 5, 2020 at 12:40 PM Arnd Bergmann <arnd@...nel.org> wrote:
> >
> > > I think this driver never worked. Looking at the original code in
> > > Linux 2.1.31, it already has the problems I fixed in commit
> > > 8fdcabeac398.
> > >
> > > I guess when people (or bots) say they "tested", they have not
> > > necessarily used this driver to actually try transporting data. They
> > > may just have tested open/close, etc. to confirm that the particular
> > > problem/issue they saw had been fixed.
> >
> > It didn't sound like that from the commit message, but it could be.
> > For reference:
> >
> https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit?id=aa2b4427c355acaf86d2c7e6fae
> a3472005e3cff
> 
> I see. The author of this commit said "I tested by bringing up an x.25
> async line using a modified version of slattach." Maybe he only
> switched TTY ports from the N_TTY line discipline to the N_X25 line
> discipline. To actually test transporting data, we need to either use
> AF_PACKET sockets, or use AF_X25 sockets with the X.25 routing table
> properly set up. The author of this commit didn't clearly indicate
> that he did these.

Hmmm.... LAPB would expect to have an X.25 level 3 and maybe ISO
transport (class 0, 2 or 3) sat on top of it.
The ISO networking service would normally be absent (more likely to
be used with class 4 transport over ethernet - but still optional).
Nothing at all like SLIP.

You could use LAPB unnumbered (UI) frames to carry IP frames
(as SLIP does) - but that is really just using HDLC instead of
async. Doing that using async is just silly.

Looks like this code should have been removed for 2.2 :-)

	David

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