tim jones article on IBM developerWorks

Tim Jones's articles ...

Anatomy of Linux journaling file systems In recent history, journaling file systems were viewed as an oddity and thought of primarily in terms of research. But today, a journaling file system (ext3) is the default in Linux. Discover the ideas behind journaling file systems, and learn how they provide better integrity in the face of a power failure or system crash. Learn about the various journaling file systems in use today, and peek into the next generation of journaling file systems.	04 Jun 2008
Anatomy of Linux flash file systems You've probably heard of Journaling Flash File System (JFFS) and Yet Another Flash File System (YAFFS), but do you know what it means to have a file system that assumes an underlying flash device? This article introduces you to flash file systems for Linux, and explores how they care for their underlying consumable devices (flash parts) through wear leveling, and identifies the various flash file systems available along with their fundamental designs.	20 May 2008
Anatomy of real-time Linux architectures It's not that Linux isn't fast or efficient, but in some cases fast just isn't good enough. What's needed instead is the ability to deterministically meet scheduling deadlines with specific tolerances. Discover the various real-time Linux alternatives and how they achieve real time -- from the early architectures that mimic virtualization solutions to the options available today in the standard 2.6 kernel.	15 Apr 2008
Desktop development for the OLPC laptop The XO laptop (of the One-Laptop-Per-Child initiative) is an inexpensive laptop project intended to help educate children around the world. The laptop includes many innovations, such as a novel, inexpensive, and durable hardware design and the use of GNU/Linux as the underlying operating system. The XO also includes an application environment written in Python with a human interface called Sugar, accessible to everyone (including kids). This article is excerpted from the developerWorks tutorial "Application development for the OLPC laptop," which takes a look at the Sugar APIs and shows how to develop and debug a graphical activity in Sugar using Python.	26 Feb 2008
Anatomy of the Linux SCSI subsystem The Small Computer Systems Interface (SCSI) is a collection of standards that define the interface and protocols for communicating with a large number of devices (predominantly storage related). Linux provides a SCSI subsystem to permit communication with these devices. Linux is a great example of a layered architecture that joins high-level drivers, such as disk or CD-ROM drivers, to a physical interface such as Fibre Channel or Serial Attached SCSI (SAS). This article introduces you to the Linux SCSI subsystem and discusses where this subsystem is going in the future.	14 Nov 2007
Anatomy of Linux synchronization methods In your Linux education, you may have learned about concurrency, critical sections, and locking, but how do you use these concepts within the kernel? This article reviews the locking mechanisms available within the 2.6 kernel, including atomic operators, spinlocks, reader/writer locks, and kernel semaphores. It also explores where each mechanism is most applicable for building safe and efficient kernel code.	31 Oct 2007
Anatomy of the Linux file system When it comes to file systems, Linux is the Swiss Army knife of operating systems. Linux supports a large number of file systems, from journaling to clustering to cryptographic. Linux is a wonderful platform for using standard and more exotic file systems and also for developing file systems. This article explores the virtual file system (VFS) -- sometimes called the virtual filesystem switch -- in the Linux kernel and then reviews some of the major structures that tie file systems together.	30 Oct 2007
System emulation with QEMU QEMU is an open source emulator for complete PC systems. In addition to emulating a processor, QEMU permits emulation of all necessary subsystems, such as networking and video hardware. It also permits emulation of advanced concepts, such as symmetric multiprocessing systems (up to 255 CPUs) and other processor architectures, such as ARM or PowerPC. This article explores QEMU and its architecture and shows how to emulate a guest operating system on a Linux host.	25 Sep 2007
Anatomy of the Linux networking stack One of the greatest features of the Linux operating system is its networking stack. It was initially a derivative of the BSD stack and is well organized with a clean set of interfaces. Its interfaces range from the protocol agnostics, such as the common sockets layer interface or the device layer, to the specific interfaces of the individual networking protocols. This article explores the structure of the Linux networking stack from the perspective of its layers and also examines some of its major structures.	27 Jun 2007
Anatomy of the Linux kernel The Linux kernel is the core of a large and complex operating system, and while it's huge, it is well organized in terms of subsystems and layers. In this article, you explore the general structure of the Linux kernel and get to know its major subsystems and core interfaces. Where possible, you get links to other IBM articles to help you dig deeper.	06 Jun 2007
Anatomy of the Linux slab allocator Good operating system performance depends in part on the operating system's ability to efficiently manage resources. In the old days, heap memory managers were the norm, but performance suffered due to fragmentation and the need for memory reclamation. Today, the Linux kernel uses a method that originated in Solaris but has been used in embedded systems for quite some time, allocating memory as objects based on their size. This article explores the ideas behind the slab allocator and examines its interfaces and their use.	15 May 2007
Sugar, the XO laptop, and One Laptop per Child One Laptop per Child (OLPC) is an organization whose mission is to develop a low-cost laptop (USD100) with accompanying software to spread computer literacy to children around the world. Because the device targets children, it must provide a novel user interface and applications that allow children to experiment with tools for expression and learning. The operating system for the OLPC is a port of the Linux kernel but with a unique interface called Sugar. In this article, learn about the Sugar human interface, see how to virtualize an OLPC laptop on a standard PC using QEMU, and take a tour of Sugar and the OLPC capabilities.	24 Apr 2007
Discover the Linux Kernel Virtual Machine Linux and flexibility go hand in hand, and the options for virtualization are no different. But recently, a change in the Linux virtualization landscape has appeared with the introduction of the Kernel virtual Machine, or KVM. KVM is the first virtualization solution to be part of the mainline Linux kernel (V2.6.20). KVM supports the virtualization of Linux guest operating systems -- even Windows with hardware that is virtualization-aware. Learn about the architecture of the Linux KVM as well as why its tight integration with the kernel may change the way you use Linux.	18 Apr 2007
Virtualization with coLinux Virtualization with VMware, Xen, and Kernel-based Virtual Machine (KVM) are all the rage these days. But did you know that you can run Linux cooperatively with Microsoft Windows? This article explores Cooperative Linux (coLinux), starting with a quick introduction to virtualization and then looking at the approach taken by coLinux. You'll also see how to get coLinux up and running on Windows.	31 Mar 2007
Kernel command using Linux system calls Linux system calls -- we use them every day. But do you know how a system call is performed from user-space to the kernel? Explore the Linux system call interface (SCI), learn how to add new system calls (and alternatives for doing so), and discover utilities related to the SCI.	21 Mar 2007
Linux and symmetric multiprocessing As evidenced by major central processing unit (CPU) vendors, multi-core processors are poised to dominate the desktop and embedded space. With multiprocessing comes greater performance but also new problems. This article explores the ideas behind multiprocessing and developing applications for Linux that exploit SMP.	14 Mar 2007
Parallelize applications for faster Linux booting One of the biggest complaints about Linux, particularly from developers, is the speed with which Linux boots. By default, Linux is a general-purpose operating system that can serve as a client desktop or server right out of the box. Because of this flexibility, Linux serves a wide base but is suboptimal for any particular configuration. This article shows you options to increase the speed with which Linux boots, including two options for parallelizing the initialization process. It also shows you how to visualize graphically the performance of the boot process.	07 Mar 2007
Virtual Linux Virtualization means many things to many people. A big focus of virtualization currently is server virtualization, or the hosting of multiple independent operating systems on a single host computer. This article explores the ideas behind virtualization and then discusses some of the many ways to implement virtualization. We also look at some of the other virtualization technologies out there, such as operating system virtualization on Linux.	29 Dec 2006
Data visualization tools for Linux Applications for graphical visualization of data on Linux are varied, from simple 2-D plots to 3-D surfaces, scientific graphics programming, and graphical simulation. Luckily, there are many open source possibilities, including gnuplot, GNU Octave, Scilab, MayaVi, Maxima, OpenDX, and others. Each has its advantages and disadvantages and targets different applications. Explore a variety of open source graphical visualization tools to better decide which is best for your application. [This article has been updated to include coverage of OpenDX - Ed.]	30 Nov 2006
Build a Web spider on Linux Web spiders are software agents that traverse the Internet gathering, filtering, and potentially aggregating information for a user. Using common scripting languages and their collection of Web modules, you can easily develop Web spiders. This article shows you how to build spiders and scrapers for Linux to crawl a Web site and gather information, stock data, in this case.	14 Nov 2006
Version control for Linux Version control systems, or source management systems, are an important aspect of modern software development. Not using one is like driving a car too fast: it's fun and you might get to your destination faster, but an accident is inevitable. This article provides an overview of Software Configuration Management (SCM) systems and their benefits, including CVS, Subversion, Arch, and Git. It also reviews the most common SCM architectures. Finally, it explores some of the new approaches that are available and how they differ from the earlier methods. [Listing 4 has been updated to reflect improvements to Git's syntax. -Ed.]	16 Oct 2006
Open source robotics toolkits Building a robot involves skills from many disciplines, including embedded firmware and hardware design, sensor selection, controls systems design, and mechanical design. But simulation environments can provide a virtual arena for testing, measuring, and visualizing robotics algorithms without the high cost (and time) of development. This article introduces you to some of the open source robotics toolkits for Linux, demonstrates their capabilities, and helps you decide which is best for you.	05 Sep 2006
Boost application performance using asynchronous I/O The most common input/output (I/O) model used in Linux is synchronous I/O. After a request is made in this model, the application blocks until the request is satisfied. This is a great paradigm because the calling application requires no central processing unit (CPU) while it awaits the completion of the I/O request. But in some cases there's a need to overlap an I/O request with other processing. The Portable Operating System Interface (POSIX) asynchronous I/O (AIO) application program interface (API) provides this capability. In this article, get an overview of the API and see how to use it.	29 Aug 2006
BusyBox simplifies embedded Linux systems BusyBox is a single executable implementation of many standard Linux utilities. BusyBox contains simple utilities, such as cat and echo, as well as larger, more complex tools, such as grep, find, mount, and telnet (albeit, with fewer options than the traditional version); some refer to BusyBox as the Swiss Army knife of utilities. This article explores the purpose of BusyBox, how it works, and why it's important for memory-constrained environments.	15 Aug 2006
Linux initial RAM disk (initrd) overview The Linux initial RAM disk (initrd) is a temporary root file system that is mounted during system boot to support the two-state boot process. The initrd contains various executables and drivers that permit the real root file system to be mounted, after which the initrd RAM disk is unmounted and its memory freed. In many embedded Linux systems, the initrd is the final root file system. This article explores the initial RAM disk for Linux 2.6, including its creation and use in the Linux kernel.	31 Jul 2006
Inside the Linux scheduler The Linux kernel continues to evolve, incorporating new technologies and gaining in reliability, scalability, and performance. One of the most important features of the 2.6 kernel is a scheduler implemented by Ingo Molnar. This scheduler is dynamic, supports load-balancing, and operates in constant time -- O(1). This article explores these attributes of the Linux 2.6 scheduler, and more.	30 Jun 2006
Inside the Linux boot process The process of booting a Linux system consists of a number of stages. But whether you're booting a standard x86 desktop or a deeply embedded PowerPC target, much of the flow is surprisingly similar. This article explores the Linux boot process from the initial bootstrap to the start of the first user-space application. Along the way, you'll learn about various other boot-related topics such as the boot loaders, kernel decompression, the initial RAM disk, and other elements of Linux boot.	31 May 2006
Better networking with SCTP The Stream Control Transmission Protocol (SCTP) is a reliable transport protocol that provides stable, ordered delivery of data between two endpoints (much like TCP) and also preserves data message boundaries (like UDP). However, unlike TCP and UDP, SCTP offers such advantages as multi-homing and multi-streaming capabilities, both of which increase availability. In this article, get to know the key features of SCTP in the Linux 2.6 kernel and take a look at the server and client source code that shows the protocol's ability to deliver multi-streaming.	28 Feb 2006
Boost socket performance on Linux The Sockets API lets you develop client and server applications that can communicate across a local network or across the world via the Internet. Like any API, you can use the Sockets API in ways that promote high performance -- or inhibit it. This article explores four ways to use the Sockets API to squeeze the greatest performance out your application and to tune the GNU/Linux environment to achieve the best results. (Editor's note: we updated Tip 3 to correct an error in the calculation for Bandwidth Delay Product (BDP), spotted by an alert reader.)	03 Feb 2006
Five pitfalls of Linux sockets programming The Sockets API is the de facto standard API for networking applications development. Although the API is simple, new developers can experience some common problems. This article identifies the most common of these pitfalls and shows you how to overcome them.	20 Sep 2005