[RFC PATCH v4 11/17] fs: Add async write file modification handling.

[Stefan Roesch <shr@fb.com>]

This adds a file_modified_async() function to return -EAGAIN if the
request either requires to remove privileges or needs to update the file
modification time. This is required for async buffered writes, so the
request gets handled in the io worker of io-uring.

Signed-off-by: Stefan Roesch <shr@fb.com>
---
 fs/inode.c         | 25 ++++++++++++++++++++++++-
 fs/xfs/xfs_file.c  |  2 +-
 include/linux/fs.h |  1 +
 3 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 4bb7f583cc6b..3a5d0fa468ab 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2137,6 +2137,27 @@ EXPORT_SYMBOL(file_update_time);
  * Return: 0 on success, negative errno on failure.
  */
 int file_modified(struct file *file)
+{
+	return file_modified_async(file, 0);
+}
+EXPORT_SYMBOL(file_modified);
+
+/**
+ * file_modified_async - handle mandated vfs changes when modifying a file
+ * @file: file that was modified
+ * @flags: kiocb flags
+ *
+ * When file has been modified ensure that special
+ * file privileges are removed and time settings are updated.
+ *
+ * If IOCB_NOWAIT is set, special file privileges will not be removed and
+ * time settings will not be updated. It will return -EAGAIN.
+ *
+ * Context: Caller must hold the file's inode lock.
+ *
+ * Return: 0 on success, negative errno on failure.
+ */
+int file_modified_async(struct file *file, int flags)
 {
 	int ret;
 	struct dentry *dentry = file_dentry(file);
@@ -2163,10 +2184,12 @@ int file_modified(struct file *file)
 	ret = file_needs_update_time(inode, file, &now);
 	if (ret <= 0)
 		return ret;
+	if (flags & IOCB_NOWAIT)
+		return -EAGAIN;
 
 	return __file_update_time(inode, file, &now, ret);
 }
-EXPORT_SYMBOL(file_modified);
+EXPORT_SYMBOL(file_modified_async);
 
 int inode_needs_sync(struct inode *inode)
 {
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 5bddb1e9e0b3..793918c83755 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -410,7 +410,7 @@ xfs_file_write_checks(
 		spin_unlock(&ip->i_flags_lock);
 
 out:
-	return file_modified(file);
+	return file_modified_async(file, iocb->ki_flags);
 }
 
 static int
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3b479d02e210..9760283af7dc 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2382,6 +2382,7 @@ static inline void file_accessed(struct file *file)
 }
 
 extern int file_modified(struct file *file);
+extern int file_modified_async(struct file *file, int flags);
 
 int sync_inode_metadata(struct inode *inode, int wait);
 
-- 
2.30.2