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

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Date:	Wed, 13 Apr 2016 09:08:36 -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 Tue, 2016-04-12 at 23:01 -0400, Matthew Wilcox wrote:
> On Tue, Apr 12, 2016 at 02:39:29PM -0600, Toshi Kani wrote:
> > 
> > To support DAX pmd mappings with unmodified applications,
> > filesystems need to align an mmap address by the pmd size.
> > 
> > @@ -708,6 +708,9 @@ const struct file_operations ext4_file_operations =
> > {
> >  	.open		= ext4_file_open,
> >  	.release	= ext4_release_file,
> >  	.fsync		= ext4_sync_file,
> > +#ifdef CONFIG_FS_DAX
> > +	.get_unmapped_area = dax_get_unmapped_area,
> > +#endif
> >  	.splice_read	= generic_file_splice_read,
> >  	.splice_write	= iter_file_splice_write,
> >  	.fallocate	= ext4_fallocate,
>
> 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.

Thanks,
-Toshi