/* this function will flush buffer on a file descriptor. */
int dfs_file_flush(struct dfs_file *fd)
/* this function will flush buffer on a file descriptor. */
int dfs_file_flush(struct dfs_file *fd)
{
    if (fd == NULL)
        return -EINVAL;
    if (fd->vnode->fops->flush == NULL)
        return -ENOSYS;
    return fd->vnode->fops->flush(fd);
}