[PATCH] fsdax: unshare: zero destination if srcmap is HOLE or UNWRITTEN

[Shiyang Ruan]

unshare copies data from source to destination. But if the source is
HOLE or UNWRITTEN extents, we should zero the destination, otherwise the
result will be unexpectable.

Fixes: d984648e428b ("fsdax,xfs: port unshare to fsdax")
Signed-off-by: Shiyang Ruan <ruansy.f...@fujitsu.com>
---
 fs/dax.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 9800b93ee14d..5d2e9b10030e 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1258,15 +1258,20 @@ static s64 dax_unshare_iter(struct iomap_iter *iter)
        /* don't bother with blocks that are not shared to start with */
        if (!(iomap->flags & IOMAP_F_SHARED))
                return length;
-       /* don't bother with holes or unwritten extents */
-       if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN)
-               return length;
 
        id = dax_read_lock();
        ret = dax_iomap_direct_access(iomap, pos, length, &daddr, NULL);
        if (ret < 0)
                goto out_unlock;
 
+       /* zero the distance if srcmap is HOLE or UNWRITTEN */
+       if (srcmap->flags & IOMAP_F_SHARED || srcmap->type == IOMAP_UNWRITTEN) {
+               memset(daddr, 0, length);
+               dax_flush(iomap->dax_dev, daddr, length);
+               ret = length;
+               goto out_unlock;
+       }
+
        ret = dax_iomap_direct_access(srcmap, pos, length, &saddr, NULL);
        if (ret < 0)
                goto out_unlock;
-- 
2.39.2