[PATCH 04/11] vfs: add a vfs helper for io_uring file pos lock

[Hao Xu <hao.xu@linux.dev>]

From: Hao Xu <howeyxu@tencent.com>

Add a vfs helper file_pos_lock_nowait() for io_uring usage. The function
have conditional nowait logic, i.e. if nowait is needed, return -EAGAIN
when trylock fails.

Signed-off-by: Hao Xu <howeyxu@tencent.com>
---
 fs/file.c            | 13 +++++++++++++
 include/linux/file.h |  2 ++
 2 files changed, 15 insertions(+)

diff --git a/fs/file.c b/fs/file.c
index 35c62b54c9d6..8e5c38f5db52 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -1053,6 +1053,19 @@ void __f_unlock_pos(struct file *f)
 	mutex_unlock(&f->f_pos_lock);
 }
 
+int file_pos_lock_nowait(struct file *file, bool nowait)
+{
+	if (!(file->f_mode & FMODE_ATOMIC_POS))
+		return 0;
+
+	if (!nowait)
+		mutex_lock(&file->f_pos_lock);
+	else if (!mutex_trylock(&file->f_pos_lock))
+		return -EAGAIN;
+
+	return 1;
+}
+
 /*
  * We only lock f_pos if we have threads or if the file might be
  * shared with another process. In both cases we'll have an elevated
diff --git a/include/linux/file.h b/include/linux/file.h
index 6e9099d29343..bcc6ba0aec50 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -81,6 +81,8 @@ static inline void fdput_pos(struct fd f)
 	fdput(f);
 }
 
+extern int file_pos_lock_nowait(struct file *file, bool nowait);
+
 DEFINE_CLASS(fd, struct fd, fdput(_T), fdget(fd), int fd)
 
 extern int f_dupfd(unsigned int from, struct file *file, unsigned flags);
-- 
2.25.1