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From: Clemens Ladisch <clemens@ladisch.de>
To: "Lorenzo Fundaró" <lfundaro@etu.utc.fr>
Cc: alsa-devel@alsa-project.org
Subject: Re: about ioctl calls
Date: Thu, 26 May 2011 12:28:03 +0200	[thread overview]
Message-ID: <4DDE2B33.1090809@ladisch.de> (raw)
In-Reply-To: <BANLkTi=NFkcwxPiwULYxtLGv+=dgjXgFdg@mail.gmail.com>

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
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  reply	other threads:[~2011-05-26 10:25 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-26 10:07 about ioctl calls Lorenzo Fundaró
2011-05-26 10:28 ` Clemens Ladisch [this message]
2011-05-26 12:37   ` Lorenzo Fundaró

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