Re: [PATCH 03/11] compat_ioctl: remove translation for sound ioctls

From: Al Viro
Date: Sun Sep 09 2018 - 00:18:37 EST

On Sat, Sep 08, 2018 at 04:28:09PM +0200, Arnd Bergmann wrote:
> The SNDCTL_* and SOUND_* commands are the old OSS user interface.
> I checked all the sound ioctl commands listed in fs/compat_ioctl.c
> to see if we still need the translation handlers. Here is what I
> found:
> - sound/oss/ is (almost) gone from the kernel, this is what actually
> needed all the translations
> - The ALSA emulation for OSS correctly handles all compat_ioctl
> commands already.
> - sound/oss/dmasound/ is the last holdout of the original OSS code,
> this is only used on arch/m68k, which has no 64-bit mode and
> hence needs no compat handlers
> - arch/um/drivers/hostaudio_kern.c may run in 64-bit mode with
> 32-bit x86 user space underneath it. This rare corner case is
> the only one that still needs the compat handlers.
> By adding a simple redirect of .compat_ioctl to .unlocked_ioctl in the
> UML driver, we can remove all the COMPATIBLE_IOCTL() annotations without
> a change in functionality. For completeness, I'm adding the same thing
> to the dmasound file, knowing that it makes no difference.

> diff --git a/arch/um/drivers/hostaudio_kern.c b/arch/um/drivers/hostaudio_kern.c
> index 7f9dbdbc4eb7..0278a642a622 100644
> --- a/arch/um/drivers/hostaudio_kern.c
> +++ b/arch/um/drivers/hostaudio_kern.c
> @@ -298,6 +298,7 @@ static const struct file_operations hostaudio_fops = {
> .write = hostaudio_write,
> .poll = hostaudio_poll,
> .unlocked_ioctl = hostaudio_ioctl,
> + .compat_ioctl = hostaudio_ioctl,

Umm... OK, seeing that it's not going to be used on s390... It's still
not quite right, though, and I'm afraid that places where we have the
same ->unlocked_ioctl and ->compat_ioctl need an audit - there probably
had been other folks who'd stepped into the same.