Re: [PATCH 08/12] linux-user: Add support for setting alsa timer enhanced read using ioctl

[Laurent Vivier <laurent@vivier.eu>]

Le 15/01/2020 à 20:51, Arnd Bergmann a écrit :
> On Wed, Jan 15, 2020 at 8:17 PM Filip Bozuta <Filip.Bozuta@rt-rk.com> wrote:
>> On 15.1.20. 17:37, Arnd Bergmann wrote:
>>> On Wed, Jan 15, 2020 at 5:32 PM Laurent Vivier <laurent@vivier.eu> wrote:
>>>> Le 15/01/2020 à 17:18, Arnd Bergmann a écrit :
>>>>> On Wed, Jan 15, 2020 at 4:53 PM Filip Bozuta <Filip.Bozuta@rt-rk.com> wrote:
>>>> Do the kernel patches add new ioctl numbers to differentiate 32bit and
>>>> 64bit time_t?
>>>
>>> Yes, though SNDRV_TIMER_IOCTL_TREAD is worse: the ioctl argument
>>> is a pure 'int' that decides what format you get when you 'read' from the
>>> same file descriptor.
>>>
>>> For emulating 64-bit on 32-bit kernels, you have to use the new
>>> SNDRV_TIMER_IOCTL_TREAD64, and for emulating 32-bit on
>>> 64-bit kernels, you probably have to return -ENOTTY to
>>> SNDRV_TIMER_IOCTL_TREAD_OLD unless you also want to
>>> emulate the read() behavior.
>>> When a 32-bit process calls SNDRV_TIMER_IOCTL_TREAD64,
>>> you can translate that into the 64-bit
>>> SNDRV_TIMER_IOCTL_TREAD_OLD.
> 
>>
>> Thank you for bringing this up to my attention. Unfortunately i have
>> some duties of academic nature in next month so i won't have much time
>> fix this bug. I will try to fix this as soon as possible.
> 
> One more thing: I just realized it gets worse when emulating cross-endian,
> as then even without calling SNDRV_TIMER_IOCTL_TREAD, reading
> data from /dev/snd/timer requires byteswapping the two words.

We already have this case with netlink and we are able to translate data
on the fly.

Thanks,
Laurent