f2fs: disallow direct IO in atomic write

Atomic write needs page cache to cache data of transaction,
direct IO should never be allowed in atomic write, detect
and deny it when open atomic write file.
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -1825,6 +1825,9 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
 	if (!S_ISREG(inode->i_mode))
 		return -EINVAL;
 
+	if (filp->f_flags & O_DIRECT)
+		return -EINVAL;
+
 	ret = mnt_want_write_file(filp);
 	if (ret)
 		return ret;