src/server/pfs/fuse/file.go
func (c *counter) wait(n int64) {
	c.mu.Lock()
	defer c.mu.Unlock()
	for c.n < n {
		c.cond.Wait()
	}
}
func (c *counter) wait(n int64) {
	c.mu.Lock()
	defer c.mu.Unlock()
	for c.n < n {
		c.cond.Wait()
	}
}
// wait until more than n bytes have been written