[RFC PATCH] file: Wrap locking mechanism for f_pos_lock

[I Hsin Cheng]

As the implementation of "f->f_pos_lock" may change in the future,
wrapping the actual implementation of locking and unlocking of it can
provide better decoupling semantics.

"__f_unlock_pos()" already exist and does that, adding "__f_lock_pos()"
can provide full decoupling.

Signed-off-by: I Hsin Cheng <richard120310@xxxxxxxxx>
---
 fs/file.c            | 7 ++++++-
 include/linux/file.h | 1 +
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/file.c b/fs/file.c
index fb1011cf6b4a..b93ac67d276d 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -1181,6 +1181,11 @@ static inline bool file_needs_f_pos_lock(struct file *file)
 		(file_count(file) > 1 || file->f_op->iterate_shared);
 }
 
+void __f_lock_pos(struct file *f)
+{
+	mutex_lock(&f->f_pos_lock);
+}
+
 struct fd fdget_pos(unsigned int fd)
 {
 	struct fd f = fdget(fd);
@@ -1188,7 +1193,7 @@ struct fd fdget_pos(unsigned int fd)
 
 	if (file && file_needs_f_pos_lock(file)) {
 		f.word |= FDPUT_POS_UNLOCK;
-		mutex_lock(&file->f_pos_lock);
+		__f_lock_pos(file);
 	}
 	return f;
 }
diff --git a/include/linux/file.h b/include/linux/file.h
index 302f11355b10..16292bd95499 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -67,6 +67,7 @@ extern struct file *fget(unsigned int fd);
 extern struct file *fget_raw(unsigned int fd);
 extern struct file *fget_task(struct task_struct *task, unsigned int fd);
 extern struct file *fget_task_next(struct task_struct *task, unsigned int *fd);
+extern void __f_lock_pos(struct file *file);
 extern void __f_unlock_pos(struct file *);
 
 struct fd fdget(unsigned int fd);
-- 
2.43.0