[PATCH v3 1/4] dax: introduce a fs_dax_get_by_bdev() helper

[Dan Williams <dan.j.williams@xxxxxxxxx>]

Add a helper that can replace the following common pattern:

	if (blk_queue_dax(bdev->bd_queue))
		fs_dax_get_by_host(bdev->bd_disk->disk_name);

This will be used to move dax_device lookup from iomap-operation time to
fs-mount time.

Cc: Jan Kara <jack@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 drivers/dax/super.c |   10 ++++++++++
 include/linux/dax.h |    6 ++++++
 2 files changed, 16 insertions(+)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 938eb4868f7f..b699aac268a6 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -46,6 +46,8 @@ void dax_read_unlock(int id)
 EXPORT_SYMBOL_GPL(dax_read_unlock);
 
 #ifdef CONFIG_BLOCK
+#include <linux/blkdev.h>
+
 int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
 		pgoff_t *pgoff)
 {
@@ -59,6 +61,14 @@ int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
 }
 EXPORT_SYMBOL(bdev_dax_pgoff);
 
+struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
+{
+	if (!blk_queue_dax(bdev->bd_queue))
+		return NULL;
+	return fs_dax_get_by_host(bdev->bd_disk->disk_name);
+}
+EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
+
 /**
  * __bdev_dax_supported() - Check if the device supports dax for filesystem
  * @sb: The superblock of the device
diff --git a/include/linux/dax.h b/include/linux/dax.h
index df97b7af7e2c..ac8afa18f707 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -57,6 +57,7 @@ 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);
 #else
 static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
 {
@@ -71,6 +72,11 @@ static inline struct dax_device *fs_dax_get_by_host(const char *host)
 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)
+{
+	return NULL;
+}
 #endif
 
 int dax_read_lock(void);