[PATCH 15/18] btrfs: handle dax page zeroing

[Goldwyn Rodrigues <rgoldwyn@xxxxxxx>]

From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>

btrfs_dax_zero_block() zeros part of the page, either from the
front or the regular rest of the block.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
---
 fs/btrfs/ctree.h |  1 +
 fs/btrfs/dax.c   | 27 ++++++++++++++++++++++++++-
 fs/btrfs/inode.c |  4 ++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index d3d044125619..ee1ed18f8b3c 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3806,6 +3806,7 @@ vm_fault_t btrfs_dax_fault(struct vm_fault *vmf);
 int btrfs_dax_file_range_compare(struct inode *src, loff_t srcoff,
 		struct inode *dest, loff_t destoff, loff_t len,
 		bool *is_same);
+int btrfs_dax_zero_block(struct inode *inode, loff_t from, loff_t len, bool front);
 #else
 static inline ssize_t btrfs_file_dax_write(struct kiocb *iocb, struct iov_iter *from)
 {
diff --git a/fs/btrfs/dax.c b/fs/btrfs/dax.c
index a29628b403b3..a4b36d5b537c 100644
--- a/fs/btrfs/dax.c
+++ b/fs/btrfs/dax.c
@@ -132,7 +132,8 @@ static int btrfs_iomap_begin(struct inode *inode, loff_t pos,
 	 * This will be true for reads only since we have already
 	 * allocated em
 	 */
-	if (em->block_start == EXTENT_MAP_HOLE) {
+	if (em->block_start == EXTENT_MAP_HOLE ||
+			em->flags == EXTENT_FLAG_FILLING) {
 		iomap->type = IOMAP_HOLE;
 		return 0;
 	}
@@ -234,4 +235,28 @@ int btrfs_dax_file_range_compare(struct inode *src, loff_t srcoff,
 {
 	return dax_file_range_compare(src, srcoff, dest, destoff, len, is_same, &btrfs_iomap_ops);
 }
+
+/*
+ * zero a part of the page only. This should CoW (via iomap_begin) if required
+ */
+int btrfs_dax_zero_block(struct inode *inode, loff_t from, loff_t len, bool front)
+{
+	loff_t start = round_down(from, PAGE_SIZE);
+	loff_t end = round_up(from, PAGE_SIZE);
+	loff_t offset = from;
+	int ret = 0;
+
+	if (front) {
+		len = from - start;
+		offset = start;
+	} else	{
+		if (!len)
+			len = end - from;
+	}
+
+	if (len)
+		ret = iomap_zero_range(inode, offset, len, NULL, &btrfs_iomap_ops);
+
+	return (ret < 0) ? ret : 0;
+}
 #endif /* CONFIG_FS_DAX */
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index c2c0544009a7..f6a64607bc8c 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4833,6 +4833,10 @@ int btrfs_truncate_block(struct inode *inode, loff_t from, loff_t len,
 	    (!len || IS_ALIGNED(len, blocksize)))
 		goto out;
 
+#ifdef CONFIG_FS_DAX
+	if (IS_DAX(inode))
+		return btrfs_dax_zero_block(inode, from, len, front);
+#endif
 	block_start = round_down(from, blocksize);
 	block_end = block_start + blocksize - 1;
 
-- 
2.16.4