dax: fix build warnings with FS_DAX and !FS_IOMAP

As reported by Arnd:

  https://lkml.org/lkml/2017/1/10/756

Compiling with the following configuration:

  # CONFIG_EXT2_FS is not set
  # CONFIG_EXT4_FS is not set
  # CONFIG_XFS_FS is not set
  # CONFIG_FS_IOMAP depends on the above filesystems, as is not set
  CONFIG_FS_DAX=y

generates build warnings about unused functions in fs/dax.c:

  fs/dax.c:878:12: warning: `dax_insert_mapping' defined but not used [-Wunused-function]
   static int dax_insert_mapping(struct address_space *mapping,
              ^~~~~~~~~~~~~~~~~~
  fs/dax.c:572:12: warning: `copy_user_dax' defined but not used [-Wunused-function]
   static int copy_user_dax(struct block_device *bdev, sector_t sector, size_t size,
              ^~~~~~~~~~~~~
  fs/dax.c:542:12: warning: `dax_load_hole' defined but not used [-Wunused-function]
   static int dax_load_hole(struct address_space *mapping, void **entry,
              ^~~~~~~~~~~~~
  fs/dax.c:312:14: warning: `grab_mapping_entry' defined but not used [-Wunused-function]
   static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index,
                ^~~~~~~~~~~~~~~~~~

Now that the struct buffer_head based DAX fault paths and I/O path have
been removed we really depend on iomap support being present for DAX.
Make this explicit by selecting FS_IOMAP if we compile in DAX support.

This allows us to remove conditional selections of FS_IOMAP when FS_DAX
was present for ext2 and ext4, and to remove an #ifdef in fs/dax.c.

Link: http://lkml.kernel.org/r/1484087383-29478-1-git-send-email-ross.zwisler@linux.intel.com
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reported-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 2 deletions

diff --git a/fs/dax.c b/fs/dax.c
index ddcddfeaa03b..3af2da5e64ce 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -990,7 +990,6 @@ int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
 }
 EXPORT_SYMBOL_GPL(__dax_zero_page_range);
 
-#ifdef CONFIG_FS_IOMAP
 static sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)
 {
 	return iomap->blkno + (((pos & PAGE_MASK) - iomap->offset) >> 9);
@@ -1428,4 +1427,3 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 }
 EXPORT_SYMBOL_GPL(dax_iomap_pmd_fault);
 #endif /* CONFIG_FS_DAX_PMD */
-#endif /* CONFIG_FS_IOMAP */