FD 4 is where things get a bit more interesting, since it is a write-only handle to a character device, essentially /dev/log.
FD 4 中的内容比较有趣，因为它是一个字符设备的只读句柄，实质上是 /dev/log。
2
Retrieve character o (log n) o (1).
检索字符o (log n) o (1)。
3
As I mentioned in the overview section, random character access on a rope with many internal nodes is approximately o (log n), so traversal is o (n log n).