fs: factor out backing_file_{read,write}_iter() helpers

Overlayfs submits files io to backing files on other filesystems.
Factor out some common helpers to perform io to backing files, into
fs/backing-file.c.

Suggested-by: Miklos Szeredi <miklos@szeredi.hu>
Link: https://lore.kernel.org/r/CAJfpeguhmZbjP3JLqtUy0AdWaHOkAPWeP827BBWwRFEAUgnUcQ@mail.gmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/include/linux/backing-file.h b/include/linux/backing-file.h
index 55c9e804f780..0648d548a418 100644
--- a/include/linux/backing-file.h
+++ b/include/linux/backing-file.h
@@ -9,9 +9,24 @@
 #define _LINUX_BACKING_FILE_H
 
 #include <linux/file.h>
+#include <linux/uio.h>
+#include <linux/fs.h>
+
+struct backing_file_ctx {
+	const struct cred *cred;
+	struct file *user_file;
+	void (*accessed)(struct file *);
+	void (*end_write)(struct file *);
+};
 
 struct file *backing_file_open(const struct path *user_path, int flags,
 			       const struct path *real_path,
 			       const struct cred *cred);
+ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
+			       struct kiocb *iocb, int flags,
+			       struct backing_file_ctx *ctx);
+ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
+				struct kiocb *iocb, int flags,
+				struct backing_file_ctx *ctx);
 
 #endif /* _LINUX_BACKING_FILE_H */