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    SubjectRe: [PATCH v2 2/5] ext4: call dax_get_unmapped_area() for DAX pmd mappings
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    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

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