[alsa-devel] about ioctl calls
clemens at ladisch.de
Thu May 26 12:28:03 CEST 2011
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
> 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.
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