[PATCH v4 4/7] iomap: Introduce iomap_apply2() for operations on two files

[Shiyang Ruan]

Some operations, such as comparing a range of data in two files under
fsdax mode, requires nested iomap_open()/iomap_end() on two file.  Thus,
we introduce iomap_apply2() to accept arguments from two files and
iomap_actor2_t for actions on two files.

Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
---
 fs/iomap/apply.c      | 52 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/iomap.h |  7 +++++-
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/apply.c b/fs/iomap/apply.c
index 26ab6563181f..0493da5286ad 100644
--- a/fs/iomap/apply.c
+++ b/fs/iomap/apply.c
@@ -97,3 +97,55 @@ iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags,
 
 	return written ? written : ret;
 }
+
+loff_t
+iomap_apply2(struct inode *ino1, loff_t pos1, struct inode *ino2, loff_t pos2,
+		loff_t length, unsigned int flags, const struct iomap_ops *ops,
+		void *data, iomap_actor2_t actor)
+{
+	struct iomap smap = { .type = IOMAP_HOLE };
+	struct iomap dmap = { .type = IOMAP_HOLE };
+	loff_t written = 0, ret, ret2 = 0;
+	loff_t len1 = length, len2, min_len;
+
+	ret = ops->iomap_begin(ino1, pos1, len1, flags, &smap, NULL);
+	if (ret)
+		goto out;
+	if (WARN_ON(smap.offset > pos1)) {
+		written = -EIO;
+		goto out_src;
+	}
+	if (WARN_ON(smap.length == 0)) {
+		written = -EIO;
+		goto out_src;
+	}
+	len2 = min_t(loff_t, len1, smap.length);
+
+	ret = ops->iomap_begin(ino2, pos2, len2, flags, &dmap, NULL);
+	if (ret)
+		goto out_src;
+	if (WARN_ON(dmap.offset > pos2)) {
+		written = -EIO;
+		goto out_dest;
+	}
+	if (WARN_ON(dmap.length == 0)) {
+		written = -EIO;
+		goto out_dest;
+	}
+	min_len = min_t(loff_t, len2, dmap.length);
+
+	written = actor(ino1, pos1, ino2, pos2, min_len, data, &smap, &dmap);
+
+out_dest:
+	if (ops->iomap_end)
+		ret2 = ops->iomap_end(ino2, pos2, len2,
+				      written > 0 ? written : 0, flags, &dmap);
+out_src:
+	if (ops->iomap_end)
+		ret = ops->iomap_end(ino1, pos1, len1,
+				     written > 0 ? written : 0, flags, &smap);
+out:
+	if (written)
+		return written;
+	return ret ?: ret2;
+}
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index d202fd2d0f91..9493c48bcc9c 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -150,10 +150,15 @@ struct iomap_ops {
  */
 typedef loff_t (*iomap_actor_t)(struct inode *inode, loff_t pos, loff_t len,
 		void *data, struct iomap *iomap, struct iomap *srcmap);
-
+typedef loff_t (*iomap_actor2_t)(struct inode *ino1, loff_t pos1,
+		struct inode *ino2, loff_t pos2, loff_t len, void *data,
+		struct iomap *smap, struct iomap *dmap);
 loff_t iomap_apply(struct inode *inode, loff_t pos, loff_t length,
 		unsigned flags, const struct iomap_ops *ops, void *data,
 		iomap_actor_t actor);
+loff_t iomap_apply2(struct inode *ino1, loff_t pos1, struct inode *ino2,
+		loff_t pos2, loff_t length, unsigned int flags,
+		const struct iomap_ops *ops, void *data, iomap_actor2_t actor);
 
 ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
 		const struct iomap_ops *ops);
-- 
2.31.0