kernelExploring the Magic of Sysfs in Linux Kernel（sysfslinux）

The Linux kernel provides many management and debugging interfaces for users, one of the most powerful is sysfs. This article will introduce what is sysfs and how it works.

Sysfs is a pseudo filesystem that exports information about various system areas such as device drivers, kernel, firmware and hardware. It was initially developed for the 2.6 Linux kernel and still continues to be a very important part of the Linux kernel.

Sysfs is a special filesystem that reads and writes variables (text and binary data) in RAM using special directory files. It is used to export firmware information and allow drivers to interact with the kernel. The sysfs directory contains a variety of information about the system, including hardware and device drivers. The sysfs filesystem emulates the behavior of a pseudo filesystem, sending data to and from the kernel.

The sysfs filesystem is populated by kernel code. Whenever a kernel module, device driver or user-space application creates or modifies a sysfs entry, it is done by writing out a pseudo file and using a special function to notify the kernel of the new file and its contents. As the kernel interpets the files, it updates its internal data structures accordingly.

Sysfs can be used to get information about the system such as device drivers, hardware, firmware and configuration parameters. We can access the sysfs filesystem in our user-space applications. For example, the following code snippet will query the sysfs directory for the list of loaded kernel modules.

#include  
#include  
int main() 
{ 
    // path to sysfs 
    const char* sysfsPath = "/sys/module"; 
    // reading the sysfs entries 
    DIR* dp = opendir(sysfsPath); 
    struct dirent* ent; 
    while (ent = readdir(dp)) 
    { 
        // printing the kernel modules 
        printf("%s\n", ent->d_name); 
    } 
    // close the directory pointer 
    closedir(dp); 
    return 0; 
} 

Sysfs can also be used to manage various configuration options. Commonly used configuration files such as bootargs, hostname, etc. can be found in the sysfs filesystem. We can also use sysfs to discover devices connected to the system. The sysfs filesystem contains directory nodes of all attached devices under the /sys/bus/USB directory.

Sysfs is an extremely powerful and versatile tool that provides a lot of useful information and control over our Linux systems. It allows us to quickly peek under the hood and get insight into our systems. In addition, sysfs also provide debugging interfaces that can be used to troubleshoot system problems. Therefore, mastering the use of sysfs is an essential skill for Linux system administrators.