Re: [PATCH] dma-buf: add support for compat ioctl

[Marek Szyprowski]

Dear All,

On 2017-02-21 15:37, Marek Szyprowski wrote:
> Hi Christian,
>
> On 2017-02-21 14:59, Christian KÃnig wrote:
> > Am 21.02.2017 um 14:21 schrieb Marek Szyprowski:
> > > Add compat ioctl support to dma-buf. This lets one to use 
> > > DMA_BUF_IOCTL_SYNC
> > > ioctl from 32bit application on 64bit kernel. Data structures for 
> > > both 32
> > > and 64bit modes are same, so there is no need for additional 
> > > translation
> > > layer.
> >
> > Well I might be wrong, but IIRC compat_ioctl was just optional and if 
> > not specified unlocked_ioctl was called instead.
> >
> > If that is true your patch wouldn't have any effect at all.
>
> Well, then why I got -ENOTTY in the 32bit test app for this ioctl on 
> 64bit ARM64 kernel without this patch?

I've checked in fs/compat_ioctl.c, I see no fallback in 
COMPAT_SYSCALL_DEFINE3,
so one has to provide compat_ioctl callback to have ioctl working with 32bit
apps.

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland