linux-kernel - Re: [PATCH v2 2/2] tty: Change order of ttynull to be loaded sooner.

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Message-ID: <8413152.MhkbZ0Pkbq@nerdopolis2>
Date: Sat, 22 Feb 2025 23:56:47 -0500
From: Adam Simonelli <adamsimonelli@...il.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
 Jiri Slaby <jirislaby@...nel.org>
Subject: Re: [PATCH v2 2/2] tty: Change order of ttynull to be loaded sooner.

On Wednesday, February 19, 2025 9:03:08 AM EST Greg Kroah-Hartman wrote:
> On Sun, Feb 16, 2025 at 11:07:48PM -0500, adamsimonelli@...il.com wrote:
> > From: Adam Simonelli <adamsimonelli@...il.com>
> > 
> > If CONFIG_NULL_TTY_CONSOLE is enabled, and CONFIG_VT is disabled, ttynull
> > will become the default primary console device, based on the load order.
> 
> You mean "link order" right?
Yeah, I'm sorry, I will change that.
> 
> > Users and distributions that are migrating away from CONFIG_VT will
> > benefit from this as /dev/console would not suddenly become /dev/ttyS0
> > which could otherwise cause some user space behavior changes, namely the
> > TCGETS ioctl failing, which causes libc's isatty() to incorrectly return
> > false when /dev/ttyS0 is disabled, and will prevent a device that is
> > connected to a user's /dev/ttyS0 to suddenly start getting kernel log
> > messages.
> 
> I'm sorry, but I can not parse that very long sentance.  If CONFIG_VT is
> not enabled, this isn't going to change anything with ttynull, it will
> just happen to have this console loaded before all others, right?
> 
> Which implies that this might break existing systems when this loads
> before the expected platform-specific drivers.  Was this tested on those
> systems?
> 
OK, next version of the patch, I think the commit message should be more more
clear I hope.
> > 
> > Signed-off-by: Adam Simonelli <adamsimonelli@...il.com>
> > ---
> >  drivers/tty/Makefile | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
> > index 07aca5184a55..03bb47e11e1c 100644
> > --- a/drivers/tty/Makefile
> > +++ b/drivers/tty/Makefile
> > @@ -11,6 +11,8 @@ obj-$(CONFIG_N_HDLC)		+= n_hdlc.o
> >  obj-$(CONFIG_N_GSM)		+= n_gsm.o
> >  
> >  obj-y				+= vt/
> > +obj-$(CONFIG_NULL_TTY)		+= ttynull.o
> 
> If you are going to rely on link order here, and HAVE to have this above
> all other consoles, please document it as such so that people have a
> hint as to why you are doing this in the file so it dosn't change again.
> 
> thanks,
> 
OK. I will add some comments
> greg k-h
>