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, 27 insertions, 7 deletions

diff --git a/include/linux/dax.h b/include/linux/dax.h
index 00ebac854bb7..5ec1f6c47716 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -18,6 +18,20 @@ struct dax_operations {
 			void **, pfn_t *);
 };
 
+#if IS_ENABLED(CONFIG_DAX)
+struct dax_device *dax_get_by_host(const char *host);
+void put_dax(struct dax_device *dax_dev);
+#else
+static inline struct dax_device *dax_get_by_host(const char *host)
+{
+	return NULL;
+}
+
+static inline void put_dax(struct dax_device *dax_dev)
+{
+}
+#endif
+
 int bdev_dax_pgoff(struct block_device *, sector_t, size_t, pgoff_t *pgoff);
 #if IS_ENABLED(CONFIG_FS_DAX)
 int __bdev_dax_supported(struct super_block *sb, int blocksize);
@@ -25,23 +39,29 @@ static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
 {
 	return __bdev_dax_supported(sb, blocksize);
 }
+
+static inline struct dax_device *fs_dax_get_by_host(const char *host)
+{
+	return dax_get_by_host(host);
+}
+
+static inline void fs_put_dax(struct dax_device *dax_dev)
+{
+	put_dax(dax_dev);
+}
+
 #else
 static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
 {
 	return -EOPNOTSUPP;
 }
-#endif
 
-#if IS_ENABLED(CONFIG_DAX)
-struct dax_device *dax_get_by_host(const char *host);
-void put_dax(struct dax_device *dax_dev);
-#else
-static inline struct dax_device *dax_get_by_host(const char *host)
+static inline struct dax_device *fs_dax_get_by_host(const char *host)
 {
 	return NULL;
 }
 
-static inline void put_dax(struct dax_device *dax_dev)
+static inline void fs_put_dax(struct dax_device *dax_dev)
 {
 }
 #endif