[RFC PATCH v2 5/7] dax: memcpy before zeroing range

[Shiyang Ruan]

From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>

However, this needed more iomap fields, so it was easier
to pass iomap and compute inside the function rather
than passing a log of arguments.

Note, there is subtle difference between iomap_sector and
dax_iomap_sector(). Can we replace dax_iomap_sector with
iomap_sector()? It would need pos & PAGE_MASK though or else
bdev_dax_pgoff() return -EINVAL.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
---
 fs/dax.c               | 21 ++++++++++++++++-----
 fs/iomap/buffered-io.c |  8 ++++----
 include/linux/dax.h    | 12 ++++++------
 3 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index a4f90f3faddb..eab6bb256205 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1117,11 +1117,16 @@ static int dax_copy_edges(loff_t pos, loff_t length, struct iomap *srcmap,
 	return ret;
 }
 
-int __dax_zero_page_range(struct block_device *bdev,
-		struct dax_device *dax_dev, sector_t sector,
-		unsigned int offset, unsigned int size)
+int __dax_zero_page_range(struct iomap *iomap, struct iomap *srcmap, loff_t pos,
+			  unsigned int offset, unsigned int size)
 {
-	if (dax_range_is_aligned(bdev, offset, size)) {
+	sector_t sector = dax_iomap_sector(iomap, pos & PAGE_MASK);
+	struct block_device *bdev = iomap->bdev;
+	struct dax_device *dax_dev = iomap->dax_dev;
+	int ret = 0;
+
+	if (iomap == srcmap &&
+	    dax_range_is_aligned(bdev, offset, size)) {
 		sector_t start_sector = sector + (offset >> 9);
 
 		return blkdev_issue_zeroout(bdev, start_sector,
@@ -1141,11 +1146,17 @@ int __dax_zero_page_range(struct block_device *bdev,
 			dax_read_unlock(id);
 			return rc;
 		}
+		if (iomap != srcmap) {
+			ret = dax_copy_edges(pos, size, srcmap, kaddr, false);
+			if (ret)
+				goto out_unlock;
+		}
 		memset(kaddr + offset, 0, size);
 		dax_flush(dax_dev, kaddr + offset, size);
+out_unlock:
 		dax_read_unlock(id);
 	}
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(__dax_zero_page_range);
 
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index c62e807956b6..3fa79389e4d0 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -960,10 +960,9 @@ static int iomap_zero(struct inode *inode, loff_t pos, unsigned offset,
 }
 
 static int iomap_dax_zero(loff_t pos, unsigned offset, unsigned bytes,
-		struct iomap *iomap)
+		struct iomap *iomap, struct iomap *srcmap)
 {
-	return __dax_zero_page_range(iomap->bdev, iomap->dax_dev,
-			iomap_sector(iomap, pos & PAGE_MASK), offset, bytes);
+	return __dax_zero_page_range(iomap, srcmap, pos, offset, bytes);
 }
 
 static loff_t
@@ -985,7 +984,8 @@ iomap_zero_range_actor(struct inode *inode, loff_t pos, loff_t count,
 		bytes = min_t(loff_t, PAGE_SIZE - offset, count);
 
 		if (IS_DAX(inode))
-			status = iomap_dax_zero(pos, offset, bytes, iomap);
+			status = iomap_dax_zero(pos, offset, bytes, iomap,
+						srcmap);
 		else
 			status = iomap_zero(inode, pos, offset, bytes, iomap,
 					srcmap);
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 4533bfb99683..7adf3b9e1061 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -12,6 +12,7 @@
 
 typedef unsigned long dax_entry_t;
 
+struct iomap;
 struct iomap_ops;
 struct dax_device;
 struct dax_operations {
@@ -226,13 +227,12 @@ int dax_file_range_compare(struct inode *src, loff_t srcoff,
 			   const struct iomap_ops *ops);
 
 #ifdef CONFIG_FS_DAX
-int __dax_zero_page_range(struct block_device *bdev,
-		struct dax_device *dax_dev, sector_t sector,
-		unsigned int offset, unsigned int length);
+int __dax_zero_page_range(struct iomap *iomap, struct iomap *srcmap, loff_t pos,
+			  unsigned int offset, unsigned int size);
 #else
-static inline int __dax_zero_page_range(struct block_device *bdev,
-		struct dax_device *dax_dev, sector_t sector,
-		unsigned int offset, unsigned int length)
+static inline int __dax_zero_page_range(struct iomap *iomap,
+					struct iomap *srcmap, loff_t pos,
+					unsigned int offset, unsigned int size)
 {
 	return -ENXIO;
 }
-- 
2.23.0