[PATCH v3 stable/linux-6.12.y 1/3] fs: constify file ptr in backing_file accessor helpers

[Cai Xinchen <caixinchen1@huawei.com>]

From: Amir Goldstein <amir73il@gmail.com>

[ Upstream commit 4e301d858af17ae2ce56886296e5458c5a08219a ]

Add internal helper backing_file_set_user_path() for the only
two cases that need to modify backing_file fields.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/20250607115304.2521155-2-amir73il@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Cai Xinchen <caixinchen1@huawei.com>
---
 fs/backing-file.c  |  4 ++--
 fs/file_table.c    | 13 ++++++++-----
 fs/internal.h      |  1 +
 include/linux/fs.h |  6 +++---
 4 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/fs/backing-file.c b/fs/backing-file.c
index 09a9be945d45..892361c31c3d 100644
--- a/fs/backing-file.c
+++ b/fs/backing-file.c
@@ -41,7 +41,7 @@ struct file *backing_file_open(const struct path *user_path, int flags,
 		return f;
 
 	path_get(user_path);
-	*backing_file_user_path(f) = *user_path;
+	backing_file_set_user_path(f, user_path);
 	error = vfs_open(real_path, f);
 	if (error) {
 		fput(f);
@@ -65,7 +65,7 @@ struct file *backing_tmpfile_open(const struct path *user_path, int flags,
 		return f;
 
 	path_get(user_path);
-	*backing_file_user_path(f) = *user_path;
+	backing_file_set_user_path(f, user_path);
 	error = vfs_tmpfile(real_idmap, real_parentpath, f, mode);
 	if (error) {
 		fput(f);
diff --git a/fs/file_table.c b/fs/file_table.c
index 2a08bc93b0b9..75a1908d51a9 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -48,17 +48,20 @@ struct backing_file {
 	struct path user_path;
 };
 
-static inline struct backing_file *backing_file(struct file *f)
-{
-	return container_of(f, struct backing_file, file);
-}
+#define backing_file(f) container_of(f, struct backing_file, file)
 
-struct path *backing_file_user_path(struct file *f)
+struct path *backing_file_user_path(const struct file *f)
 {
 	return &backing_file(f)->user_path;
 }
 EXPORT_SYMBOL_GPL(backing_file_user_path);
 
+void backing_file_set_user_path(struct file *f, const struct path *path)
+{
+	backing_file(f)->user_path = *path;
+}
+EXPORT_SYMBOL_GPL(backing_file_set_user_path);
+
 static inline void backing_file_free(struct backing_file *ff)
 {
 	path_put(&ff->user_path);
diff --git a/fs/internal.h b/fs/internal.h
index 8c1b7acbbe8f..a4352d333c61 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -100,6 +100,7 @@ extern void chroot_fs_refs(const struct path *, const struct path *);
 struct file *alloc_empty_file(int flags, const struct cred *cred);
 struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred);
 struct file *alloc_empty_backing_file(int flags, const struct cred *cred);
+void backing_file_set_user_path(struct file *f, const struct path *path);
 
 static inline void file_put_write_access(struct file *file)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 87720e1b5419..70bbc00a2bd2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2738,7 +2738,7 @@ 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 path *backing_file_user_path(struct file *f);
+struct path *backing_file_user_path(const struct file *f);
 
 /*
  * When mmapping a file on a stackable filesystem (e.g., overlayfs), the file
@@ -2750,14 +2750,14 @@ struct path *backing_file_user_path(struct file *f);
  * by fstat() on that same fd.
  */
 /* Get the path to display in /proc/<pid>/maps */
-static inline const struct path *file_user_path(struct file *f)
+static inline const struct path *file_user_path(const struct file *f)
 {
 	if (unlikely(f->f_mode & FMODE_BACKING))
 		return backing_file_user_path(f);
 	return &f->f_path;
 }
 /* Get the inode whose inode number to display in /proc/<pid>/maps */
-static inline const struct inode *file_user_inode(struct file *f)
+static inline const struct inode *file_user_inode(const struct file *f)
 {
 	if (unlikely(f->f_mode & FMODE_BACKING))
 		return d_inode(backing_file_user_path(f)->dentry);
-- 
2.18.0.huawei.25