Book Image

Mastering Embedded Linux Programming

By : Chris Simmonds
Book Image

Mastering Embedded Linux Programming

By: Chris Simmonds

Overview of this book

Mastering Embedded Linux Programming takes you through the product cycle and gives you an in-depth description of the components and options that are available at each stage. You will begin by learning about toolchains, bootloaders, the Linux kernel, and how to configure a root filesystem to create a basic working device. You will then learn how to use the two most commonly used build systems, Buildroot and Yocto, to speed up and simplify the development process. Building on this solid base, the next section considers how to make best use of raw NAND/NOR flash memory and managed flash eMMC chips, including mechanisms for increasing the lifetime of the devices and to perform reliable in-field updates. Next, you need to consider what techniques are best suited to writing applications for your device. We will then see how functions are split between processes and the usage of POSIX threads, which have a big impact on the responsiveness and performance of the final device The closing sections look at the techniques available to developers for profiling and tracing applications and kernel code using perf and ftrace.
Table of Contents (22 chapters)
Mastering Embedded Linux Programming
About the Author
About the Reviewers

After the kernel has booted

We saw in Chapter 4, Porting and Configuring the Kernel, how the kernel bootstrap code seeks to find a root filesystem, either initramfs or a filesystem specified by root= on the kernel command line, and then to execute a program which, by default, is /init for initramfs, and /sbin/init for a regular filesystem. The init program has root privilege and since it is the first process to run, it has a process ID (PID) of 1. If, for some reason, init cannot be started, the kernel will panic.

The init program is the ancestor of all other processes, as shown here by the pstree command, which is part of the psmisc package in most distrubutions:

# pstree -gn


The job of the init program is to take control of the system and set it running. It may be as simple as a shell command running a shell script – there is an example at the start of Chapter 5, Building a Root Filesystem—but...