Re: [PATCH 07/33] tty: vt: use _IO() to define ioctl numbers

Christophe Leroy
2025-07-31T14:50:39Z

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

Christophe