linux-kernel - Re: [PATCH v2 2/5] ext4: call dax_get_unmapped

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Message-ID: <1460573564.24985.60.camel@hpe.com>
Date:	Wed, 13 Apr 2016 12:52:44 -0600
From:	Toshi Kani <toshi.kani@....com>
To:	Matthew Wilcox <willy@...ux.intel.com>
Cc:	akpm@...ux-foundation.org, dan.j.williams@...el.com,
	linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Jan Kara <jack@...e.cz>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2 2/5] ext4: call dax_get_unmapped_area() for DAX pmd
 mappings

On Wed, 2016-04-13 at 14:22 -0400, Matthew Wilcox wrote:
> On Wed, Apr 13, 2016 at 09:08:36AM -0600, Toshi Kani wrote:
> > 
> > > 
> > > Could you do something like:
> > > 
> > >  #ifdef CONFIG_FS_DAX
> > >  struct page *read_dax_sector(struct block_device *bdev, sector_t n);
> > > +unsigned long dax_get_unmapped_area(struct file *filp, unsigned long
> > > addr,
> > > +               unsigned long len, unsigned long pgoff, unsigned long
> > > flags);
> > >  #else
> > >  static inline struct page *read_dax_sector(struct block_device
> > > *bdev,
> > >                  sector_t n)
> > >  {
> > >          return ERR_PTR(-ENXIO);
> > >  }
> > > +#define dax_get_unmapped_area	NULL
> > >  #endif
> > > 
> > > in patch 1/5.  Then there's no need for the ifdefs in each
> > > filesystem.
> >
> > I thought about it, but I do not think we can use an inline function to
> > an entry point.
>
> That's not an inline function.  It's just NULL.  So after the
> preprocessor is done with it, it just looks like:
> 
> 	.get_unmapped_area = NULL,
> 
> and it won't be called by get_unmapped_area().

Oh, I see. Good idea. I will do that.

Thanks,
-Toshi