Merge tag 'ovl-vfs-6.8' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/overlayfs/vfs

Pull backing file updates from Amir Goldstein:

These patches essentially just lift some overlayfs code to common code.
The motivation is to reuse common stacking code for the FUSE passthrough
patches that I am shaping up for upstream. The FUSE passthrough work
will be coming in over the next cycles.

I have been testing those patches with my fuse-backing-fd development
branch for quite some time and I think both you and Miklos gave a
conceptual ACK to some version of this work.

* tag 'ovl-vfs-6.8' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/overlayfs/vfs:
  fs: factor out backing_file_mmap() helper
  fs: factor out backing_file_splice_{read,write}() helpers
  fs: factor out backing_file_{read,write}_iter() helpers
  fs: prepare for stackable filesystems backing file helpers

Signed-off-by: Christian Brauner <brauner@kernel.org>

2 files changed, 42 insertions, 3 deletions

diff --git a/include/linux/backing-file.h b/include/linux/backing-file.h
new file mode 100644
index 000000000000..3f1fe1774f1b
--- /dev/null
+++ b/include/linux/backing-file.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Common helpers for stackable filesystems and backing files.
+ *
+ * Copyright (C) 2023 CTERA Networks.
+ */
+
+#ifndef _LINUX_BACKING_FILE_H
+#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);
+ssize_t backing_file_splice_read(struct file *in, loff_t *ppos,
+				 struct pipe_inode_info *pipe, size_t len,
+				 unsigned int flags,
+				 struct backing_file_ctx *ctx);
+ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
+				  struct file *out, loff_t *ppos, size_t len,
+				  unsigned int flags,
+				  struct backing_file_ctx *ctx);
+int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
+		      struct backing_file_ctx *ctx);
+
+#endif /* _LINUX_BACKING_FILE_H */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 900d0cd55b50..db5d07e6e02e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2575,9 +2575,6 @@ struct file *dentry_open(const struct path *path, int flags,
 			 const struct cred *creds);
 struct file *dentry_create(const struct path *path, int flags, umode_t mode,
 			   const struct cred *cred);
-struct file *backing_file_open(const struct path *user_path, int flags,
-			       const struct path *real_path,
-			       const struct cred *cred);
 struct path *backing_file_user_path(struct file *f);
 
 /*