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

[Marek Szyprowski <m.szyprowski@samsung.com>]

Dear All,

On 2017-02-21 15:37, Marek Szyprowski wrote:
> Hi Christian,
>
> On 2017-02-21 14:59, Christian König 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