3 files changed, 52 insertions, 3 deletions

diff --git a/fs/libfs.c b/fs/libfs.c
index 7ff3cb904acd..0fb590d79f30 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1060,6 +1060,45 @@ int noop_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 }
 EXPORT_SYMBOL(noop_fsync);
 
+int noop_set_page_dirty(struct page *page)
+{
+        /*
+         * Unlike __set_page_dirty_no_writeback that handles dirty page
+         * tracking in the page object, dax does all dirty tracking in
+         * the inode address_space in response to mkwrite faults. In the
+         * dax case we only need to worry about potentially dirty CPU
+         * caches, not dirty page cache pages to write back.
+         *
+         * This callback is defined to prevent fallback to
+         * __set_page_dirty_buffers() in set_page_dirty().
+         */
+        return 0;
+}
+EXPORT_SYMBOL_GPL(noop_set_page_dirty);
+
+void noop_invalidatepage(struct page *page, unsigned int offset,
+                unsigned int length)
+{
+        /*
+         * There is no page cache to invalidate in the dax case, however
+         * we need this callback defined to prevent falling back to
+         * block_invalidatepage() in do_invalidatepage().
+         */
+}
+EXPORT_SYMBOL_GPL(noop_invalidatepage);
+
+ssize_t noop_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
+{
+        /*
+         * iomap based filesystems support direct I/O without need for
+         * this callback. However, it still needs to be set in
+         * inode->a_ops so that open/fcntl know that direct I/O is
+         * generally supported.
+         */
+        return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(noop_direct_IO);
+
 /* Because kfree isn't assignment-compatible with void(void*) ;-/ */
 void kfree_link(void *p)
 {
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 0185ecdae135..ae27a7efe7ab 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -38,6 +38,7 @@ static inline void put_dax(struct dax_device *dax_dev)
 }
 #endif
 
+struct writeback_control;
 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);
@@ -57,6 +58,8 @@ static inline void fs_put_dax(struct dax_device *dax_dev)
 }
 
 struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
+int dax_writeback_mapping_range(struct address_space *mapping,
+                struct block_device *bdev, struct writeback_control *wbc);
 #else
 static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
 {
@@ -76,6 +79,12 @@ static inline struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
 {
         return NULL;
 }
+
+static inline int dax_writeback_mapping_range(struct address_space *mapping,
+                struct block_device *bdev, struct writeback_control *wbc)
+{
+        return -EOPNOTSUPP;
+}
 #endif
 
 int dax_read_lock(void);
@@ -121,7 +130,4 @@ static inline bool dax_mapping(struct address_space *mapping)
         return mapping->host && IS_DAX(mapping->host);
 }
 
-struct writeback_control;
-int dax_writeback_mapping_range(struct address_space *mapping,
-                struct block_device *bdev, struct writeback_control *wbc);
 #endif
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 79c413985305..44f7f7080faa 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3129,6 +3129,10 @@ extern int simple_rmdir(struct inode *, struct dentry *);
 extern int simple_rename(struct inode *, struct dentry *,
                          struct inode *, struct dentry *, unsigned int);
 extern int noop_fsync(struct file *, loff_t, loff_t, int);
+extern int noop_set_page_dirty(struct page *page);
+extern void noop_invalidatepage(struct page *page, unsigned int offset,
+                unsigned int length);
+extern ssize_t noop_direct_IO(struct kiocb *iocb, struct iov_iter *iter);
 extern int simple_empty(struct dentry *);
 extern int simple_readpage(struct file *file, struct page *page);
 extern int simple_write_begin(struct file *file, struct address_space *mapping,