Re: [ALSA patch] [PATCH - alsa-lib 4/4] pcm_file: add infile read support for mmap mode

["Takashi Sakamoto" <o-takashi@sakamocchi.jp>]

Hi,

On Tue, May 21, 2019, at 17:52, Takashi Iwai wrote:
> On Tue, 21 May 2019 10:37:43 +0200,
> Miartus, Adam (Arion Recruitment; ADITG/ESM) wrote:
> > 
> > > On Mon, 20 May 2019 18:51:06 +0200,
> > > Miartus, Adam (Arion Recruitment; ADITG/ESM) wrote:
> > > >
> > > > From: Adam Miartus <amiartus@de.adit-jv.com>
> > > >
> > > > mmap_begin callback is used to copy data from input file to mmaped
> > > > buffer
> > > >
> > > > guard for corner use of api (multiple mmap_begin calls by user) is
> > > > introduced to check if next continuous buffer was already overwritten
> > > >
> > > > buffer is overwritten with input file data only in case of stream
> > > > capture
> > > >
> > > > Signed-off-by: Adam Miartus <amiartus@de.adit-jv.com>
> > > > Reviewed-by: Timo Wischer <twischer@de.adit-jv.com>
> > > 
> > > Can't we copy the data in snd_pcm_file_mmap_commit() just like the
> > > playback case?
> > > 
> > > 
> > > thanks,
> > > 
> > > Takashi
> > 
> > My understanding is that in case of reading data in mmap mode user
> > would call mmap_begin, read the buffer and then call mmap_commit.
> > 
> > In this case overwriting the buffer in mmap_commit with data from
> > Input file would be too late. 
> 
> Hm, OK.  I basically hate to add a new ops, but this might be the only
> way if we have to implement that.

I'm interested in this patch, however the patch is not blasted by list server.
Would you please re-post your patchset so that the list server delivers them
to subscribers and I can see the contents?

> OTOH, is this mmap support mandatory?  IOW, is wrapping with the plug
> and mmap_emul performance-wise so bad?


Regards

Takashi Sakamoto