fsdax,xfs: port unshare to fsdax

Implement unshare in fsdax mode: copy data from srcmap to iomap.

Link: https://lkml.kernel.org/r/1669908753-169-1-git-send-email-ruansy.fnst@fujitsu.com
Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/dax.c

@@ -1245,6 +1245,58 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
 }
 #endif /* CONFIG_FS_DAX_PMD */
 
+static s64 dax_unshare_iter(struct iomap_iter *iter)
+{
+	struct iomap *iomap = &iter->iomap;
+	const struct iomap *srcmap = iomap_iter_srcmap(iter);
+	loff_t pos = iter->pos;
+	loff_t length = iomap_length(iter);
+	int id = 0;
+	s64 ret = 0;
+	void *daddr = NULL, *saddr = NULL;
+
+	/* 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;
+
+	ret = dax_iomap_direct_access(srcmap, pos, length, &saddr, NULL);
+	if (ret < 0)
+		goto out_unlock;
+
+	ret = copy_mc_to_kernel(daddr, saddr, length);
+	if (ret)
+		ret = -EIO;
+
+out_unlock:
+	dax_read_unlock(id);
+	return ret;
+}
+
+int dax_file_unshare(struct inode *inode, loff_t pos, loff_t len,
+		const struct iomap_ops *ops)
+{
+	struct iomap_iter iter = {
+		.inode		= inode,
+		.pos		= pos,
+		.len		= len,
+		.flags		= IOMAP_WRITE | IOMAP_UNSHARE | IOMAP_DAX,
+	};
+	int ret;
+
+	while ((ret = iomap_iter(&iter, ops)) > 0)
+		iter.processed = dax_unshare_iter(&iter);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dax_file_unshare);
+
 static int dax_memzero(struct iomap_iter *iter, loff_t pos, size_t size)
 {
 	const struct iomap *iomap = &iter->iomap;

fs/xfs/xfs_reflink.c

@@ -1693,6 +1693,10 @@ xfs_reflink_unshare(
 
 	inode_dio_wait(inode);
 
+	if (IS_DAX(inode))
+		error = dax_file_unshare(inode, offset, len,
+				&xfs_dax_write_iomap_ops);
+	else
 		error = iomap_file_unshare(inode, offset, len,
 				&xfs_buffered_write_iomap_ops);
 	if (error)

include/linux/dax.h

@@ -205,6 +205,8 @@ static inline void dax_unlock_mapping_entry(struct address_space *mapping,
 }
 #endif
 
+int dax_file_unshare(struct inode *inode, loff_t pos, loff_t len,
+		const struct iomap_ops *ops);
 int dax_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
 		const struct iomap_ops *ops);
 int dax_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,