[PATCH 05/29] vfs: add a vfs helper for io_uring file pos lock

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From: Hao Xu <howeyxu@xxxxxxxxxxx>

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@xxxxxxxxxxx>
 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)
+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)
+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);

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