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Linux Systems Programming

Robert Love
Published by O'Reilly Media
388 pages
£ 30.99
Published: October 2007
reviewed by Alain Williams
   in the December 2007 issue (pdf), (html)

If you want to start C programming on a Linux system this book is for you. Its aim is to introduce you to the system calls that you will need as well as some of glibc (the GNU C library).

The book is more than a copy of the manual pages, it has that with a discussion on why or alternative ways of doing it and then illustrates the system call with a code fragment, often complete programs that you can compile and run. Some of the chapters contain a few pages on what the kernel has to do to provide the system calls described.

The first real chapter is on file I/O: open(), close(), read(), write(), creating, seeking. Blocking and non blocking I/O with select() and poll(). There are comments on portability of some constructs. The next chapter covers the same area but using the stdio library: fopen() and friends. Interesting comments on thread safety. Chapter 4 is about Advanced File I/O: scatter/gather I/O, Epoll(), memory mapped and asynchronous I/O and file advice hints to the kernel.

Next is processes: what they are, getpid(), the exec family, fork(), and a lot on wait()ing. Uids (what different ones a process has), sessions and process groups. Process scheduling in the kernel is discussed although that is already going out of date since it seems to be a favourite re-write area of the kernel hackers; but the system calls to manipulate the various priorities, real time scheduling are well worth reading.

Half way through the book we reach file and directory management: the traditional stat(), chmod() and also POSIX extended attributes: getxattr(), etc. Then directory manipulation: mkdir(), readdir(), links. I learned a lot about the file monitoring systems calls, the inotify family, these will tell a process when something has happened to a file.

Memory management is mainly at the glibc malloc() and posix additions level. How to set malloc options and get statistics is covered. Memory manipulation memcpy() is followed by memory locking. Signals come next, this includes a list of reentrant functions.

The last chapter is on time: time of day, how to measure and sleep for intervals, what POSIX has to say about it. I always find time more complicated than I think it ought to be. System time setting with adjtime() is talked about, I still didn't understand all of it but I suspect that no one other than David L Mills (who wrote it) really does.

I found the appendix on GCC Extensions to the C language interesting.

I came across the book because I was looking for one that contained all the funny Linux calls that you don't see on other Unix systems, things like: clone(), splice() and sync_file_range(); also C program startup (linking of shared objects) and the magic behind 32 and 64 bit file offset sizes. This book does not talk about them, a book with these would be useful.

Summary: worth while getting if you want to write in C on a Linux box, but disappointing that it does not cover more of the uniquely Linux system calls.

Disclosure: I was one of the technical reviewers of the book.

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