Re: [PATCH 00/11] ALSA: firewire-motu: add ioctl commands to retrieve information in messages delivered by isoc packet

[Takashi Sakamoto <o-takashi@sakamocchi.jp>]

Hi,

On Mon, Oct 18, 2021 at 02:57:29PM +0200, Takashi Iwai wrote:
> On Mon, 18 Oct 2021 14:46:54 +0200,
> Takashi Sakamoto wrote:
> > 
> > Hi,
> > 
> > On Mon, Oct 18, 2021 at 10:05:32AM +0200, Takashi Iwai wrote:
> > > On Sun, 17 Oct 2021 11:25:37 +0200,
> > > Takashi Sakamoto wrote:
> > > > 
> > > > Would I ask you opinion about my concern about firewire UAPI header? Is
> > > > it allowed to use float type instead of __u32 type?
> > > 
> > > I guess the safest way would be like include/uapi/linux/acct.h.
> > > The ifdef KERNEL will be omitted at installation, so user-space would
> > > see only float type while the kernel sees only __u32.
> > 
> > Yes. I've already found the header and it would be the safest, However,
> > conditional macro sometimes confuses userspace developers...
> 
> I believe that the ifdef will be dropped automagically during
> installing the files, so that user-space will see only float.
> 
> You can try to patch and run make headers_install.

Oh, I thought that the headers are simply copied when installing...
Indeed, I can find 'scripts/headers_install.sh' does the work in
'headers' make target invoked by the 'headers_install' target.

```
$ tail -n10 include/uapi/sound/firewire.h 
 */
struct snd_firewire_motu_command_dsp_meter {
#ifdef __KERNEL__
	__u32 data[SNDRV_FIREWIRE_MOTU_COMMAND_DSP_METER_COUNT];
#else
	float data[SNDRV_FIREWIRE_MOTU_COMMAND_DSP_METER_COUNT];
#endif
};

#endif /* _UAPI_SOUND_FIREWIRE_H_INCLUDED */
$ make headers
$ tail -n5 usr/include/sound/firewire.h 
 */
struct snd_firewire_motu_command_dsp_meter {
	float data[SNDRV_FIREWIRE_MOTU_COMMAND_DSP_METER_COUNT];
};

#endif /* _SOUND_FIREWIRE_H_INCLUDED */
```

It would be achieved to use different type with the same storage size
between kernel and userspace. After writing some userspace test
applications, I'll post the patch. Thanks for your advice.

> Takashi


Regards

Takashi Sakamoto