Stock span

Given a list of daily closing prices, the span on day $i$ is the number of consecutive days ending at day $i$ (including day $i$ itself) whose close is at most the close on day $i$. For prices 100, 80, 60, 70, 60, 75, 85 the spans are 1, 1, 1, 2, 1, 4, 6. Compute every span in $O(n)$ time.