dax: introduce dax_operations

Track a set of dax_operations per dax_device that can be set at
alloc_dax() time. These operations will be used to stop the abuse of
block_device_operations for communicating dax capabilities to
filesystems. It will also be used to replace the "pmem api" and move
pmem-specific cache maintenance, and other dax-driver-specific
filesystem-dax operations, to dax device methods. In particular this
allows us to stop abusing __copy_user_nocache(), via memcpy_to_pmem(),
with a driver specific replacement.

This is a standalone introduction of the operations. Follow on patches
convert each dax-driver and teach fs/dax.c to use ->direct_access() from
dax_operations instead of block_device_operations.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 8d446674c1da..1a58542ee8fd 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -17,6 +17,7 @@
 #include <linux/cdev.h>
 #include <linux/hash.h>
 #include <linux/slab.h>
+#include <linux/dax.h>
 #include <linux/fs.h>
 
 static int nr_dax = CONFIG_NR_DEV_DAX;
@@ -61,6 +62,7 @@ struct dax_device {
 	const char *host;
 	void *private;
 	bool alive;
+	const struct dax_operations *ops;
 };
 
 bool dax_alive(struct dax_device *dax_dev)
@@ -208,7 +210,8 @@ static void dax_add_host(struct dax_device *dax_dev, const char *host)
 	spin_unlock(&dax_host_lock);
 }
 
-struct dax_device *alloc_dax(void *private, const char *__host)
+struct dax_device *alloc_dax(void *private, const char *__host,
+		const struct dax_operations *ops)
 {
 	struct dax_device *dax_dev;
 	const char *host;
@@ -229,6 +232,7 @@ struct dax_device *alloc_dax(void *private, const char *__host)
 		goto err_dev;
 
 	dax_add_host(dax_dev, host);
+	dax_dev->ops = ops;
 	dax_dev->private = private;
 	return dax_dev;