linux-ext4 - [PATCH 04/11] vfs: add a vfs helper for io

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Date:   Sun, 27 Aug 2023 21:28:28 +0800
From:   Hao Xu <hao.xu@...ux.dev>
To:     io-uring@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Cc:     Dominique Martinet <asmadeus@...ewreck.org>,
        Pavel Begunkov <asml.silence@...il.com>,
        Christian Brauner <brauner@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Stefan Roesch <shr@...com>, Clay Harris <bugs@...ycon.org>,
        Dave Chinner <david@...morbit.com>,
        "Darrick J . Wong" <djwong@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-cachefs@...hat.com,
        ecryptfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-unionfs@...r.kernel.org, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-btrfs@...r.kernel.org, codalist@...a.cs.cmu.edu,
        linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com,
        linux-mm@...ck.org, linux-nilfs@...r.kernel.org,
        devel@...ts.orangefs.org, linux-cifs@...r.kernel.org,
        samba-technical@...ts.samba.org, linux-mtd@...ts.infradead.org,
        Wanpeng Li <wanpengli@...cent.com>
Subject: [PATCH 04/11] vfs: add a vfs helper for io_uring file pos lock

From: Hao Xu <howeyxu@...cent.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@...cent.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