dax: fix up some of the block device related ifdefs

The DAX device <-> block device association is only enabled if
CONFIG_BLOCK is enabled.  Update dax.h to account for that and use
the right conditions for the fs_put_dax stub as well.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20211129102203.2243509-28-hch@lst.deSigned-off-by: Dan Williams <dan.j.williams@intel.com>

include/linux/dax.h

@@ -108,24 +108,15 @@ static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
 #endif
 
 struct writeback_control;
-#if IS_ENABLED(CONFIG_FS_DAX)
+#if defined(CONFIG_BLOCK) && defined(CONFIG_FS_DAX)
 int dax_add_host(struct dax_device *dax_dev, struct gendisk *disk);
 void dax_remove_host(struct gendisk *disk);
-
+struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev,
+		u64 *start_off);
 static inline void fs_put_dax(struct dax_device *dax_dev)
 {
 	put_dax(dax_dev);
 }
-
-struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev,
-		u64 *start_off);
-int dax_writeback_mapping_range(struct address_space *mapping,
-		struct dax_device *dax_dev, struct writeback_control *wbc);
-
-struct page *dax_layout_busy_page(struct address_space *mapping);
-struct page *dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end);
-dax_entry_t dax_lock_page(struct page *page);
-void dax_unlock_page(struct page *page, dax_entry_t cookie);
 #else
 static inline int dax_add_host(struct dax_device *dax_dev, struct gendisk *disk)
 {
@@ -134,17 +125,25 @@ static inline int dax_add_host(struct dax_device *dax_dev, struct gendisk *disk)
 static inline void dax_remove_host(struct gendisk *disk)
 {
 }
-
-static inline void fs_put_dax(struct dax_device *dax_dev)
-{
-}
-
 static inline struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev,
 		u64 *start_off)
 {
 	return NULL;
 }
+static inline void fs_put_dax(struct dax_device *dax_dev)
+{
+}
+#endif /* CONFIG_BLOCK && CONFIG_FS_DAX */
 
+#if IS_ENABLED(CONFIG_FS_DAX)
+int dax_writeback_mapping_range(struct address_space *mapping,
+		struct dax_device *dax_dev, struct writeback_control *wbc);
+
+struct page *dax_layout_busy_page(struct address_space *mapping);
+struct page *dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end);
+dax_entry_t dax_lock_page(struct page *page);
+void dax_unlock_page(struct page *page, dax_entry_t cookie);
+#else
 static inline struct page *dax_layout_busy_page(struct address_space *mapping)
 {
 	return NULL;