[PATCH 15/15] fs: create {sb,file}_write_not_started() helpers

From: Amir Goldstein <amir73il@gmail.com>
To: Christian Brauner <brauner@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>,
	Jens Axboe <axboe@kernel.dk>, Miklos Szeredi <miklos@szeredi.hu>,
	David Howells <dhowells@redhat.com>,
	linux-fsdevel@vger.kernel.org
Subject: [PATCH 15/15] fs: create {sb,file}_write_not_started() helpers
Date: Tue, 14 Nov 2023 17:33:21 +0200	[thread overview]
Message-ID: <20231114153321.1716028-16-amir73il@gmail.com> (raw)
In-Reply-To: <20231114153321.1716028-1-amir73il@gmail.com>

Create new helpers {sb,file}_write_not_started() that can be used
to assert that sb_start_write() is not held.

This is needed for fanotify "pre content" events.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 include/linux/fs.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 05780d993c7d..c085172f832f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1669,6 +1669,17 @@ static inline bool sb_write_started(const struct super_block *sb)
 	return __sb_write_started(sb, SB_FREEZE_WRITE);
 }
 
+/**
+ * sb_write_not_started - check if SB_FREEZE_WRITE is not held
+ * @sb: the super we write to
+ *
+ * May be false positive with !CONFIG_LOCKDEP/LOCK_STATE_UNKNOWN.
+ */
+static inline bool sb_write_not_started(const struct super_block *sb)
+{
+	return __sb_write_started(sb, SB_FREEZE_WRITE) <= 0;
+}
+
 /**
  * file_write_started - check if SB_FREEZE_WRITE is held
  * @file: the file we write to
@@ -1684,6 +1695,21 @@ static inline bool file_write_started(const struct file *file)
 	return sb_write_started(file_inode(file)->i_sb);
 }
 
+/**
+ * file_write_not_started - check if SB_FREEZE_WRITE is not held
+ * @file: the file we write to
+ *
+ * May be false positive with !CONFIG_LOCKDEP/LOCK_STATE_UNKNOWN.
+ * May be false positive with !S_ISREG, because file_start_write() has
+ * no effect on !S_ISREG.
+ */
+static inline bool file_write_not_started(const struct file *file)
+{
+	if (!S_ISREG(file_inode(file)->i_mode))
+		return true;
+	return sb_write_not_started(file_inode(file)->i_sb);
+}
+
 /**
  * sb_end_write - drop write access to a superblock
  * @sb: the super we wrote to
-- 
2.34.1

