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

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Message-ID: <9fffb5be-eced-4207-86fc-8939de1ab16e@kernel.org>
Date: Fri, 1 Aug 2025 06:47:46 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Nicolas Pitre <nico@...xnic.net>,
 Christophe Leroy <christophe.leroy@...roup.eu>
Cc: 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 31. 07. 25, 22:58, Nicolas Pitre wrote:
> 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.

Oh, right -- it's easy to revert (no conflicts).

We could use _IOC(0, 'V', number, 0) directly, but I am not sure, that's 
worth it.

thanks,
-- 
js
suse labs