Summary

In this chapter, we discussed the fundamentals of block devices and we looked at the data structures used by the block I/O layer: The bio, representing in-flight I/O; the buffer_head, representing a block-to-page mapping; and the request structure, representing a specific I/O request. We followed the I/O request on its brief but important life, culminating in the I/O scheduler. We discussed the dilemmas involved in scheduling I/O and went over the four I/O schedulers currently in the Linux kernel, as well as the old Linus Elevator from 2.4.

Next up, we will tackle the process address space.