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

Hao Xu
2023-08-25T13:57:16Z

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