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Kernel and driver development for the Linux kernel

Core Technology

Article from ADMIN 23/2014

By Jürgen Quade and Eva-Katharina Kunst

The /proc filesystem facilitates the exchange of current data between the system and user. To access the data, you simply read and write to a file. This mechanism is the first step for understanding kernel programming. ü

In keeping with the central Unix philosophy that everything is a file, Linux systems publish system information through the virtual filesystems /proc and /sys (see the "Proc Filesystem" box). This brilliant mechanism gives the user read and write access to system internals with the read() and write() functions.

Proc Filesystem

The /proc virtual filesystem folders and files are not stored on a hard disk; rather, the kernel creates them dynamically on access. The term "proc" derives from "processes"; thus, it is clear that the /proc filesystem primarily provides information about computing processes (Figure 1).

For each computational process, the kernel creates a new directory with the process identification number as its name. Below the directory, you find extensive information about the job, including the call parameters (cmdline), shared file descriptors (fd) and environment variables (environ), and process statistics.

In addition to information about computing processes, the kernel uses the virtual filesystem to share information with the user system and receive configurations. All data for the current CPU is in /proc/cpuinfo, interrupt sources and the frequency of their occurrence is under /proc/interrupts, and info for activated device drivers with their device numbers is under /proc/devices. Writing 1 to /proc/sys/net/ipv4/ip_forward enables routing in the Linux kernel and configures the watchdog feature when written to /proc/sys/kernel/watchdog. KL:Navigating the /proc filesystem is both useful and instructive. A proc file name reveals how important a file in

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