linux-kernel - Re: [PATCHES] tty ioctls cleanups, compat and not only

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Message-ID: <CAK8P3a3LD58jnwP38OpnEWHMzAAfrqtfjHamWVU5PwaKoWyKjg@mail.gmail.com>
Date:   Thu, 13 Sep 2018 22:56:48 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     gregkh <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHES] tty ioctls cleanups, compat and not only

On Thu, Sep 13, 2018 at 10:31 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Thu, Sep 13, 2018 at 01:19:42PM +0200, Arnd Bergmann wrote:
> > On Thu, Sep 13, 2018 at 4:31 AM Al Viro <viro@...iv.linux.org.uk> wrote:
> > * TIOCSERGWILD/TIOCSERSWILD are obsolete and never do
> >    anything useful, but the return code is inconsistent: ENOTTY
> >    in compat mode vs 0 in uart_ioctl, plus a printk for amiserial.
> >    If we want to keep it around rather than deleting it completely,
> >    it should be marked as compatible.
>
> Yes.  Not sure if we want to - the only user is setserial(8), with
>        -W     Do wild interrupt initialization and exit.  This  option  is  no
>               longer relevant in Linux kernels after version 2.1.
>
> What's more, rc.serial does *not* use it since 2.15 and even in 2.14 it wouldn't
> have failed the boot - just whine (truthfully) "Cannot scan for wild interrupts"
> on stderr and continue with the rest of the script.  The same goes at least as
> far back as setserial-2.02.  That's what MCC had; if you want to check something
> earlier, you'll probably have to ask tytso, but I very much doubt that anything
> of that vintage will work with the current kernels *or* that anyone cared to
> abort the script in question on setserial -W /dev/cua0 failing to start with.
>
> So I'd seriously suggest removing those altogether.  I mean, sure, we can carry
> explicit "obsolete, quietly return 0 on those" indefinitely, but that really feels
> over the top.  Time to bury the body, unless somebody objects...

Sounds good to me.

> > * PPPIOCGCHAN/PPPIOCGUNIT are implemented by multiple
> >    ldisc variants, marking them as compatible would save us from
> >    implementing a comp_ioctl method for each one separately.
> >    These are also used on some things that are not ttys though,
> >    so we can't remove them from fs/compat_ioctl.c yet.
>
> Worse - there's ipwireless, which implements it in tty_operations ->ioctl().

Yes, I saw that too, but couldn't figure out exactly what ipwireless
does. I suppose it is some serial port driver that comes with a
hardcoded ppp implementation instead of a switchable ldisc?

> > * SIOCGIFNAME, SIOCGIFENCAP, SIOCSIFENCAP,
> >   SIOCSIFHWADDR, SIOCSKEEPALIVE, SIOCGKEEPALIVE,
> >   SIOCSOUTFILL,  and SIOCGOUTFILL  are in the tty_ioctl
> >   functions for multiple protocol handlers, comparable to
> >   the PPP ones.
>
> Very definitely shared with sockets, and I prefer to handle the tty-side cases
> in ldisc ->compat_ioctl().

Fair enough.

        Arnd