From: Darrick J. Wong <djwong@kernel.org>

Create a function that ensures that the storage backing part of a file
contains zeroes and will not trip over old media errors if the contents
are re-read.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/iomap/direct-io.c  |   75 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/iomap.h |    3 ++
 2 files changed, 78 insertions(+)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 4ecd255e0511..48826a49f976 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c

@@ -652,3 +652,78 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	return iomap_dio_complete(dio);
 }
 EXPORT_SYMBOL_GPL(iomap_dio_rw);
+
+static loff_t
+iomap_zeroinit_iter(struct iomap_iter *iter)
+{
+	struct iomap *iomap = &iter->iomap;
+	const struct iomap *srcmap = iomap_iter_srcmap(iter);
+	const u64 start = iomap->addr + iter->pos - iomap->offset;
+	const u64 nr_bytes = iomap_length(iter);
+	sector_t sector = start >> SECTOR_SHIFT;
+	sector_t nr_sectors = nr_bytes >> SECTOR_SHIFT;
+	int ret;
+
+	if (!iomap->bdev)
+		return -ECANCELED;
+
+	/* The physical extent must be sector-aligned for block layer APIs. */
+	if ((start | nr_bytes) & (SECTOR_SIZE - 1))
+		return -EINVAL;
+
+	/* Must be able to zero storage directly without fs intervention. */
+	if (iomap->flags & IOMAP_F_SHARED)
+		return -ECANCELED;
+	if (srcmap != iomap)
+		return -ECANCELED;
+
+	switch (iomap->type) {
+	case IOMAP_MAPPED:
+		ret = blkdev_issue_zeroout(iomap->bdev, sector, nr_sectors,
+				GFP_KERNEL, 0);