[alsa-devel] about ioctl calls

[Clemens Ladisch]

Lorenzo Fundaró wrote:
> I have a program that constantly make ioctl calls like this:
> 
> ioctl(4, 0x4122, 0x8b703)
> ioctl(4, 0x4122, 0xbfb65768)
> 
> I suspect that this call pertains to ALSA, since I have straced other
> programs that play music and they always use in the ioctl request field the
> 0x4122 code.

This is SNDRV_PCM_IOCTL_HWSYNC.

> I am interested on finding out what's in the third argument of the ioctl
> call,
> is it a sort of struct that contains the audio samples ?

The samples and some control structures are in mmap()ed memory.
This ioctl tells the kernel to synchronize and update hardware status.

There is no third parameter; the values shown are random stack contents.


Regards,
Clemens