[resend PATCH v2 04/33] dax: introduce dax_operations

[Dan Williams]

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 <h...@lst.de>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
---
 drivers/dax/dax.h    |    4 +++-
 drivers/dax/device.c |    6 +++++-
 drivers/dax/super.c  |    6 +++++-
 include/linux/dax.h  |   10 ++++++++++
 4 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/dax/dax.h b/drivers/dax/dax.h
index 246a24d68d4c..617bbc24be2b 100644
--- a/drivers/dax/dax.h
+++ b/drivers/dax/dax.h
@@ -13,7 +13,9 @@
 #ifndef __DAX_H__
 #define __DAX_H__
 struct dax_device;
-struct dax_device *alloc_dax(void *private, const char *host);
+struct dax_operations;
+struct dax_device *alloc_dax(void *private, const char *host,
+               const struct dax_operations *ops);
 void put_dax(struct dax_device *dax_dev);
 bool dax_alive(struct dax_device *dax_dev);
 void kill_dax(struct dax_device *dax_dev);
diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index db68f4fa8ce0..a0db055054a4 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -645,7 +645,11 @@ struct dev_dax *devm_create_dev_dax(struct dax_region 
*dax_region,
                goto err_id;
        }
 
-       dax_dev = alloc_dax(dev_dax, NULL);
+       /*
+        * No 'host' or dax_operations since there is no access to this
+        * device outside of mmap of the resulting character device.
+        */
+       dax_dev = alloc_dax(dev_dax, NULL, NULL);
        if (!dax_dev)
                goto err_dax;
 
diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index bb22956a106b..45ccfc043da8 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)
@@ -204,7 +206,8 @@ 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;
@@ -225,6 +228,7 @@ 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;
 
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 9b2d5ba10d7d..74ebb92b625a 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -7,6 +7,16 @@
 #include <asm/pgtable.h>
 
 struct iomap_ops;
+struct dax_device;
+struct dax_operations {
+       /*
+        * direct_access: translate a device-relative
+        * logical-page-offset into an absolute physical pfn. Return the
+        * number of pages available for DAX at that pfn.
+        */
+       long (*direct_access)(struct dax_device *, pgoff_t, long,
+                       void **, pfn_t *);
+};
 
 int dax_read_lock(void);
 void dax_read_unlock(int id);