fsnotify: use accessor to set FMODE_NONOTIFY_*

The FMODE_NONOTIFY_* bits are a 2-bits mode.  Open coding manipulation
of those bits is risky.  Use an accessor file_set_fsnotify_mode() to
set the mode.

Rename file_set_fsnotify_mode() => file_set_fsnotify_mode_from_watchers()
to make way for the simple accessor name.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20250203223205.861346-2-amir73il@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

include/linux/fs.h

@@ -222,7 +222,6 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 #define FMODE_FSNOTIFY_HSM(mode)	0
 #endif
 
-
 /*
  * Attribute flags.  These should be or-ed together to figure out what
  * has been changed!
@@ -3140,6 +3139,12 @@ static inline void exe_file_allow_write_access(struct file *exe_file)
 	allow_write_access(exe_file);
 }
 
+static inline void file_set_fsnotify_mode(struct file *file, fmode_t mode)
+{
+	file->f_mode &= ~FMODE_FSNOTIFY_MASK;
+	file->f_mode |= mode;
+}
+
 static inline bool inode_is_open_for_write(const struct inode *inode)
 {
 	return atomic_read(&inode->i_writecount) > 0;