linux-kernel - Re: [PATCH 00/13] tty.h cleanups

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Message-ID: <YHADHYKMhfYE1aNw@hovoldconsulting.com>
Date:   Fri, 9 Apr 2021 09:32:45 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Jiri Slaby <jirislaby@...nel.org>
Subject: Re: [PATCH 00/13] tty.h cleanups

On Thu, Apr 08, 2021 at 08:01:08PM +0200, Greg Kroah-Hartman wrote:
> On Thu, Apr 08, 2021 at 04:25:22PM +0200, Johan Hovold wrote:
> > On Thu, Apr 08, 2021 at 02:51:21PM +0200, Greg Kroah-Hartman wrote:
> > > Turns out there is a lot of tty-internal stuff in include/linux/tty.h
> > > that do not belong there.  Create a internal-to-the-tty-layer .h file
> > > for these types of things and move function prototypes to it instead of
> > > being in the system-wide header file.
> > > 
> > > Along the way clean up the use of some old tty-only debugging macros and
> > > use the in-kernel dev_*() calls instead.
> > 
> > I'm afraid that's not a good idea since not all ttys have a
> > corresponding class device. Notable exception include pseudo terminals
> > and serdev.
> > 
> > While dev_printk() can handle a NULL device argument without crashing,
> > we'll actually lose log information by removing the tty printk helpers.
> 
> I think the same info will be printed here as before, just some NULL
> information at the beginning, right?  And the benifits overall (for real
> tty devices), should outweigh the few devices that do not have this
> information.

No, you'll only be losing information (tty driver and tty name). Here's
a pty example, where the first line in each pair use dev_info() and the
second tty_info():

[   10.235331] (NULL device *): tty_get_device
[   10.235441] ptm ptm0: tty_get_device

[   10.235586] (NULL device *): tty_get_device
[   10.235674] pts pts0: tty_get_device

and similar for serdev, which is becoming more and more common.

Johan