[alsa-devel] clarification on mmap

Harsha, Priya priya.harsha at intel.com
Mon Feb 23 17:51:24 CET 2009

Thank you. Can I use .ack callback to know that the mmaped buffer has been filled by the user? How would I know how much the user has written into the buffer that time? 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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