linux-kernel - Re: [PATCH 4/4] ALSA: add dummy function to support shared mmap in nommu Blackfin arch

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Date:	Tue, 02 Sep 2008 11:41:36 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	"Cai, Cliff" <Cliff.Cai@...log.com>
Cc:	"Bryan Wu" <cooloney@...nel.org>, <perex@...ex.cz>,
	<liam.girdwood@...fsonmicro.com>,
	<broonie@...nsource.wolfsonmicro.com>,
	<alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] ALSA: add dummy function to support shared mmap in nommu Blackfin arch

At Tue, 2 Sep 2008 11:16:37 +0800,
Cai, Cliff wrote:
> 
>  
> > @@ -3419,5 +3426,6 @@ const struct file_operations snd_pcm_f_ops[2] =
> {
> >  		.compat_ioctl = 	snd_pcm_ioctl_compat,
> >  		.mmap =			snd_pcm_mmap,
> >  		.fasync =		snd_pcm_fasync,
> > +		.get_unmapped_area =	dummy_get_unmapped_area,
> >  	}
> >  };
> 
> >I don't think adding this dummy get_unmapped_area unconditionally for
> every driver is good.  This overrides the default
> >mm->get_unmaped_area.
> But without this dummy function,shared mmap on nommu arch would
> fail,refer to validate_mmap_request() in mm/nommu.c.

Yes, I know it's needed for nommu.  That's why I wrote
"unconditionally" in the above.

> May be we can add a kernel config item to include or not include this
> function depending on non-mmu or mmu arch.  

Checking CONFIG_MMU may suffice?


Takashi
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