Source Code Secrets
Authors: William Jolitz and Lynne Jolitz
Publisher: Peer-to-Peer Communications
Pages: 530 (hard cover)
Reviewer: Phil Hughes
Before you get too excited about a new book about the Linux kernel, let me clear the air—The Basic Kernel is about 386BSD. If you are a savvy OS person, you've already figured that out from the names of the authors; Bill and Lynne Jolitz are the creators of 386BSD. So, why review it? Because it is a good book that covers the internals of operating systems design—and 386BSD, the system it covers, is available in source code.
The Basic Kernel is the first volume in a series entitled Operating System Source Code Secrets. The second book in the series is titled Virtual Memory. The first thirty pages of the book explain why such a book is necessary, and define both what a kernel is and the notation used in the book.
The book then talks about what code needs to be done for the kernel, presenting code fragments with explanations. About 60 pages cover the assembly code necessary to interface to the 386 processor. Not being a 386 assembly language programmer (but having extensive systems programming experience), I had some problems here. The explanations were clearly for someone with an assembly language background. I would have liked to see more in the way of “how it works” explanations. However, if you are interested in 386 code, it is probably fine.
I felt more comfortable with the next chapter, covering C code. The beginning of that chapter is typical of what follows, so I will use it as an example. The trap.c routine is introduced, along with a listing and brief explanation of its functions, followed by a detailed explanation of what the functions are, how to call them and how they are implemented. The implementation details consist of code fragments with text explanations.
The book continues in this style, covering i386/trap.c, i386/cpu.c, kern/config.c, kern/malloc.c, kern/fork.c, kern/exit.c, kern/sig.c, kern/cred.c, kern/priv.c, kern/synch.c, kern/lock.c, kern/execve.c and kern/descrip.c. If you have looked at or worked with a POSIX kernel, you can probably guess what functions are found in these files.
Three appendices cover kernel source organization, network-level security and dynamic make files. The book ends with answers to the exercises included in the chapters, and an index with entries for all the functions described.
The book is well-written, and, I expect, accurate. If you want to know how the 386BSD kernel works, this book will tell you. And, if you want to know how to implement low-level functionality that requires dealing with 386 hardware, this book has a wealth of information on the subject.
What this book won't tell you is how Linux is implemented. While the same sort of tasks have to be done in Linux, different design decisions were made for 386BSD than for Linux. As I was reading the text, many times I was thinking, “Gee, I wonder if this is done the same way in Linux?” If that comparison is of interest to you, buying both The Basic Kernel and Linux Kernel Internals (reviewed in Linux Journal, December, 1996) would probably fill your needs.
Phil Hughes is the publisher of Linux Journal.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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