dax: remove default copy_from_iter fallback

Require all dax-drivers to register a ->copy_from_iter() operation so
that it is clear which dax_operations are optional and which must be
implemented for filesystem-dax to operate.

Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

arch/powerpc/sysdev/axonram.c

@@ -45,6 +45,7 @@
 #include <linux/of_device.h>
 #include <linux/of_platform.h>
 #include <linux/pfn_t.h>
+#include <linux/uio.h>
 
 #include <asm/page.h>
 #include <asm/prom.h>
@@ -163,8 +164,15 @@ axon_ram_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pa
 	return __axon_ram_direct_access(bank, pgoff, nr_pages, kaddr, pfn);
 }
 
+static size_t axon_ram_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff,
+		void *addr, size_t bytes, struct iov_iter *i)
+{
+	return copy_from_iter(addr, bytes, i);
+}
+
 static const struct dax_operations axon_ram_dax_ops = {
 	.direct_access = axon_ram_dax_direct_access,
+	.copy_from_iter = axon_ram_copy_from_iter,
 };
 
 /**

drivers/block/brd.c

@@ -22,6 +22,7 @@
 #ifdef CONFIG_BLK_DEV_RAM_DAX
 #include <linux/pfn_t.h>
 #include <linux/dax.h>
+#include <linux/uio.h>
 #endif
 
 #include <linux/uaccess.h>
@@ -354,8 +355,15 @@ static long brd_dax_direct_access(struct dax_device *dax_dev,
 	return __brd_direct_access(brd, pgoff, nr_pages, kaddr, pfn);
 }
 
+static size_t brd_dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff,
+		void *addr, size_t bytes, struct iov_iter *i)
+{
+	return copy_from_iter(addr, bytes, i);
+}
+
 static const struct dax_operations brd_dax_ops = {
 	.direct_access = brd_dax_direct_access,
+	.copy_from_iter = brd_dax_copy_from_iter,
 };
 #endif
 

drivers/dax/super.c

@@ -179,8 +179,6 @@ size_t dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
 	if (!dax_alive(dax_dev))
 		return 0;
 
-	if (!dax_dev->ops->copy_from_iter)
-		return copy_from_iter(addr, bytes, i);
 	return dax_dev->ops->copy_from_iter(dax_dev, pgoff, addr, bytes, i);
 }
 EXPORT_SYMBOL_GPL(dax_copy_from_iter);

drivers/s390/block/dcssblk.c

@@ -18,6 +18,7 @@
 #include <linux/interrupt.h>
 #include <linux/platform_device.h>
 #include <linux/pfn_t.h>
+#include <linux/uio.h>
 #include <linux/dax.h>
 #include <asm/extmem.h>
 #include <asm/io.h>
@@ -43,8 +44,15 @@ static const struct block_device_operations dcssblk_devops = {
 	.release 	= dcssblk_release,
 };
 
+static size_t dcssblk_dax_copy_from_iter(struct dax_device *dax_dev,
+		pgoff_t pgoff, void *addr, size_t bytes, struct iov_iter *i)
+{
+	return copy_from_iter(addr, bytes, i);
+}
+
 static const struct dax_operations dcssblk_dax_ops = {
 	.direct_access = dcssblk_dax_direct_access,
+	.copy_from_iter = dcssblk_dax_copy_from_iter,
 };
 
 struct dcssblk_dev_info {

include/linux/dax.h

@@ -16,7 +16,7 @@ struct dax_operations {
 	 */
 	long (*direct_access)(struct dax_device *, pgoff_t, long,
 			void **, pfn_t *);
-	/* copy_from_iter: dax-driver override for default copy_from_iter */
+	/* copy_from_iter: required operation for fs-dax direct-i/o */
 	size_t (*copy_from_iter)(struct dax_device *, pgoff_t, void *, size_t,
 			struct iov_iter *);
 	/* flush: optional driver-specific cache management after writes */