reviewed the second edition
It has been well over five years since LWN
of Robert Love's
Linux Kernel Development
. Needless to say, things have changed a
little since the 2.6.10 release covered by that edition. As it happens,
the third edition has been out for a few months now; your editor has
finally had a chance to read through his copy and put together a review.
In summary, the third edition is a much-needed update, and Linux Kernel
remains a valuable resource, but there are some
disappointments to be found as well.
One has to dig a little bit to figure out which kernel version is covered
by the third edition; according to the preface, the target is 2.6.34.
Robert, ever the optimist, suggests that it will be good for a long time:
"As the Linux kernel matures, there is a greater chance of a snapshot
of the kernel remaining representative long into the future." Time
The third edition has been extensively updated, but it retains the same
structure as its predecessors. The preface talks of "all-new" chapters,
but the number of chapters remains the same. The scheduler discussion has
been updated to reflect the merging of the completely fair scheduler. Other
relatively recent kernel changes (mutexes, for example) have been added,
and there are changes throughout to reflect what has happened over the last
24 kernel releases.
There is a new chapter on kernel data structures; it contains
the linked list discussion previously found in Appendix A, along with
coverage of FIFOs, red-black trees, and the idr subsystem. The low-level
device model chapter has been combined with the chapter on loadable
modules, for some reason, but the discussion is not much changed. The
appendix on the random number generator is gone.
All told, the coverage of the core kernel is well written and clear, in an
approachable style. Linux Kernel Development is, at this time,
probably the best reference available for developers wanting to learn how
the kernel works and how the major pieces fit together. Your editor is
glad to have a copy on hand.
With that understanding in place, this, too, must be said: the update to
the third edition appears to have been done in a hurry. As a result, the
book contains a number of errors and inconsistencies, and it fails to cover
no end of interesting things which have happened in the kernel over the
last five years while retaining text which was obsolete even in previous
editions. Robert has not been hugely present in the kernel development
community in the last few years (he got a job at a company with a
reputation for removing developers from the community) and, unfortunately,
For example, this book (which covers 2.6.34) includes a section on the
anticipatory I/O scheduler - which was removed in 2.6.33. There is still
talk of the "Linus" scheduler - which (as is noted in the book) was a 2.4
feature. The mutual exclusion chapter discusses semaphores - which have
been deprecated for mutual exclusion purposes - with the section on mutexes
seemingly bolted on afterward.
(The book also says elsewhere that we cannot kill a process in an
uninterruptible sleep because it "may hold a semaphore")
There is a lengthy discussion of the old
"bottom half" mechanism which is long gone; the removed-in-2.5 task queue
mechanism also merits a section of its own. The unlamented
ksymoops tool, we are told, "probably came with your
Some things are simply wrong. We're told that do_exit() calls
del_timer_sync(), but that last happened in 2.6.15. The workqueue
discussion appears to be stuck in a 2.6.10 time warp; changes which were
merged for 2.6.20 are not reflected here. Kernel stack size is said to be
16K on 64-bit architectures because they usually have 8K pages. The
version of struct file shown on page 279 never existed; it
includes f_ep_lock which was renamed (by your editor) to
f_lock in 2.6.30. The "process address space" chapter says,
several times, that all Linux systems have three-level page tables, despite
the fact that the fourth level was added for 2.6.11. The device model
chapter no longer mentions struct subsystem, but it still appears
in the associated diagram.
And many things which should be discussed in a contemporary book aren't.
Developers working on the kernel now should probably be familiar with
control groups, contemporary debugging tools (kmemleak, lockdep, the fault
injection framework, ...), debugfs, ftrace, git, high-resolution timers, huge
pages, linux-next, multiple slab allocators, namespaces, perf, power
management and quality of service, read-copy-update, readahead, reverse
mapping in the VM subsystem, scheduler domains, splice(),
TASK_KILLABLE, threaded interrupt handlers, virtualization, and so on.
No book on the kernel can hope to be complete and still be something that a
person of ordinary strength can physically lift, but these topics are all
important enough that, one would assume, at least some of them would merit
coverage, but none are mentioned in the third edition.
Keeping up with all that is happening in the kernel is hard - your editor
hopes that readers will trust him to understand this. So it is not
surprising that some mistakes would slip through when a book is
fast-forwarded from 2.6.10 to 2.6.34. But the amount of old stuff that
leaked through, combined with the things which should have been mentioned
but weren't, seems a bit high; some of them should, at least, have been
caught in technical review. As a result, the third edition of Linux
Kernel Development is not as good as it could have been.
These grumbles notwithstanding, your editor will restate what was said
above: this book remains
the best overview of contemporary kernel development available today.
Robert is a talented and engaging writer who is able to cover complex
topics in a readily understandable manner. The third edition merits a
place on the "L1 bookshelf" (the one which can be reached without getting
out of the chair); developers who are working with the kernel will
probably want a copy.
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