We can now build xfs while CONFIG_DAX is set to 'm', resulting in a
link error when xfs is built-in:

fs/xfs/xfs_iomap.o: In function `xfs_file_iomap_end':
fs/xfs/xfs_iomap.c:1152: undefined reference to `put_dax'
fs/xfs/xfs_iomap.o: In function `xfs_file_iomap_begin':
fs/xfs/xfs_iomap.c:1071: undefined reference to `dax_get_by_host'

Previously, XFS could only be built with CONFIG_DAX=y because of
the CONFIG_BLOCK dependency. The other users of dax handle this
differently:

- In ext2 and ext4, there are checks for CONFIG_FS_DAX around every
  API usage, and CONFIG_FS_DAX is only enabled when CONFIG_DAX is
  built-in.

- CONFIG_BLK_DEV_MD implies 'select DAX', so it's always enabled
  there as well.

This changes XFS to do the same as ext2/4 and only call into the
API conditionally.

Fixes: ef51042472f5 ("block, dax: move "select DAX" from BLOCK to FS_DAX")
Signed-off-by: Arnd Bergmann <[email protected]>
---
 fs/xfs/xfs_iomap.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index a63f61c256bd..b732ba6f892c 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1067,7 +1067,7 @@ xfs_file_iomap_begin(
 
        /* optionally associate a dax device with the iomap bdev */
        bdev = iomap->bdev;
-       if (blk_queue_dax(bdev->bd_queue))
+       if (IS_ENABLED(CONFIG_FS_DAX) && blk_queue_dax(bdev->bd_queue))
                iomap->dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
        else
                iomap->dax_dev = NULL;
@@ -1149,7 +1149,9 @@ xfs_file_iomap_end(
        unsigned                flags,
        struct iomap            *iomap)
 {
-       put_dax(iomap->dax_dev);
+       if (IS_ENABLED(CONFIG_FS_DAX))
+               put_dax(iomap->dax_dev);
+
        if ((flags & IOMAP_WRITE) && iomap->type == IOMAP_DELALLOC)
                return xfs_file_iomap_end_delalloc(XFS_I(inode), offset,
                                length, written, iomap);
-- 
2.9.0

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