dax, xfs, ext4: compile out iomap-dax paths in the FS_DAX=n case

Tetsuo reports:

  fs/built-in.o: In function `xfs_file_iomap_end':
  xfs_iomap.c:(.text+0xe0ef9): undefined reference to `put_dax'
  fs/built-in.o: In function `xfs_file_iomap_begin':
  xfs_iomap.c:(.text+0xe1a7f): undefined reference to `dax_get_by_host'
  make: *** [vmlinux] Error 1
  $ grep DAX .config
  CONFIG_DAX=m
  # CONFIG_DEV_DAX is not set
  # CONFIG_FS_DAX is not set

When FS_DAX=n we can/must throw away the dax code in filesystems.
Implement 'fs_' versions of dax_get_by_host() and put_dax() that are
nops in the FS_DAX=n case.

Cc: <linux-xfs@vger.kernel.org>
Cc: <linux-ext4@vger.kernel.org>
Cc: Jan Kara <jack@suse.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Tested-by: Tony Luck <tony.luck@intel.com>
Fixes: ef51042472f5 ("block, dax: move 'select DAX' from BLOCK to FS_DAX")
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 26d77f9f8c12..2dcbd5698884 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -817,7 +817,7 @@ static int ext2_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
         iomap->bdev = bdev;
         iomap->offset = (u64)first_block << blkbits;
         if (blk_queue_dax(bdev->bd_queue))
-                iomap->dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
+                iomap->dax_dev = fs_dax_get_by_host(bdev->bd_disk->disk_name);
         else
                 iomap->dax_dev = NULL;
 
@@ -841,7 +841,7 @@ static int
 ext2_iomap_end(struct inode *inode, loff_t offset, loff_t length,
                 ssize_t written, unsigned flags, struct iomap *iomap)
 {
-        put_dax(iomap->dax_dev);
+        fs_put_dax(iomap->dax_dev);
         if (iomap->type == IOMAP_MAPPED &&
             written < length &&
             (flags & IOMAP_WRITE))