linux-kernel - Re: [PATCH 07/33] tty: vt: use

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Message-ID: <9811012p-4q9q-284q-n2qr-7597s16p8sq5@syhkavp.arg>
Date: Thu, 31 Jul 2025 16:58:41 -0400 (EDT)
From: Nicolas Pitre <nico@...xnic.net>
To: Christophe Leroy <christophe.leroy@...roup.eu>
cc: "Jiri Slaby (SUSE)" <jirislaby@...nel.org>, gregkh@...uxfoundation.org, 
    Christian Zigotzky <chzigotzky@...osoft.de>, linux-serial@...r.kernel.org, 
    linux-kernel@...r.kernel.org, 
    "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 07/33] tty: vt: use _IO() to define ioctl numbers

On Thu, 31 Jul 2025, Christophe Leroy wrote:

> 
> 
> Le 31/07/2025 à 16:35, Christophe Leroy a écrit :
> > Hi Jiri,
> > 
> > Le 11/06/2025 à 12:02, Jiri Slaby (SUSE) a écrit :
> >> _IO*() is the proper way of defining ioctl numbers. All these vt numbers
> >> were synthetically built up the same way the _IO() macro does.
> >>
> >> So instead of implicit hex numbers, use _IO() properly.
> >>
> >> To not change the pre-existing numbers, use only _IO() (and not _IOR()
> >> or _IOW()). The latter would change the numbers indeed.
> > 
> > On powerpc your assumption is wrong, because _IOC_NONE is not 0:
> > 
> > $ git grep _IOC_NONE arch/powerpc/
> > arch/powerpc/include/uapi/asm/ioctl.h:#define _IOC_NONE 1U
> > 
> > Therefore the value changes even with _IO(), leading to failure of Xorg as
> > reported by Christian.
> > 
> 
> And is likely an issue on the 4 following architectures:
> 
> $ git grep _IOC_NONE arch/ | grep 1U
> arch/alpha/include/uapi/asm/ioctl.h:#define _IOC_NONE	1U
> arch/mips/include/uapi/asm/ioctl.h:#define _IOC_NONE	1U
> arch/powerpc/include/uapi/asm/ioctl.h:#define _IOC_NONE	1U
> arch/sparc/include/uapi/asm/ioctl.h:#define _IOC_NONE        1U

IMHO this one patch could simply be reverted and the "old" code let be.


Nicolas