[alsa-devel] Query regarding pcm->private_data

Clemens Ladisch cladisch at fastmail.net
Mon Jun 18 09:43:20 CEST 2007

Pharaoh . wrote:
> I am reading 'Wring an alsa driver'.  It says following about the
> private_data:
> You can allocate a record for the substream and store it in
> runtime->private_data. Usually, this is done in the open callback.
> Don't mix this with pcm->private_data. The pcm->private_data usually
> points the chip instance assigned statically at the creation of PCM, while the
> runtime->private_data points a dynamic data created at the PCM open callback.
> What does static and dynamic mean here?

Nothing much.  "Static" just means that this is not allocated/freed
together with a stream's runtime.  The my_chip data is usually allocated
from the heap, but the runtime->private_data is _more_ dynamic because
it is allocated every time a stream is opened.


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