[alsa-devel] clarification on mmap
tiwai at suse.de
Mon Feb 23 20:25:15 CET 2009
At Mon, 23 Feb 2009 22:21:24 +0530,
Harsha, Priya wrote:
> Thank you. Can I use .ack callback to know that the mmaped buffer
> has been filled by the user?
Not really. It's just for explicit read/write modes.
> How would I know how much the user has
> written into the buffer that time?
You can check appl_ptr at any time. This corresponds to the position
the app has filled.
> Would I need to have the pointers
> calculated and tracked myself or is there a field in the structures
> that I can read and find out?
> -----Original Message-----
> From: Takashi Iwai [mailto:tiwai at suse.de]
> Sent: Monday, February 23, 2009 8:57 PM
> To: Harsha, Priya
> Cc: alsa-devel at alsa-project.org
> Subject: Re: clarification on mmap
> At Mon, 23 Feb 2009 18:59:11 +0530,
> Harsha, Priya wrote:
> > Hi,
> > I have a question on mmap. If I give my .info to be _MMAP and
> > _MMAP_VALID. Will ALSA framework internally take care of mmap-ing
> > the kernel buffer that has been pre-allocated in the .probe call? Do
> > I need to do anything special to mmap a kernel buffer into user
> > space? Just accessing the runtime->dma_area would allow me to access
> > user data right?
> Yes. The buffers allocated via preallocator are supposed to be
> mmappable, so you can simply pass _MMAP* flag there.
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