Summary - Kernel basics

Combine syscall and ioctl to write a system info tool.

Summary - Kernel basics

In this group you learned the boundary between the kernel and user programs: mode switching, system calls, ioctl for device control, the /proc virtual filesystem and dmesg logs.

Kernel services are always invoked through numbered syscalls. Devices are controlled with ioctl commands; /proc exposes state as text; dmesg shows the log buffer. Next you'll write a mini task that combines the five concepts. Move on to the code step when ready.

Exercise Print kernel info

Define void print_kernel_info(const char *topic, const char *detail) with body printf("%s -> %s\n", topic, detail);. In main call it for five topics: ("kernel", "mode"), ("syscall", "trap"), ("ioctl", "device"), ("proc", "vfs"), ("dmesg", "log").

Show example solution

#include <stdio.h>

void print_kernel_info(const char *topic, const char *detail) {
    printf("%s -> %s\n", topic, detail);
}

int main(void) {
    print_kernel_info("kernel", "mode");
    print_kernel_info("syscall", "trap");
    print_kernel_info("ioctl", "device");
    print_kernel_info("proc", "vfs");
    print_kernel_info("dmesg", "log");
    return 0;
}

What's next?

Congratulations! You've completed the kernel basics. You now know how a user program reaches the kernel: ask for services with syscall, control devices with ioctl, read state from /proc and watch logs with dmesg.

The next group moves to driver basics: loading kernel modules, logging with printk, device numbers with dev_t and the file_operations structure. It builds on what you learned here. Continue when you're ready.

Test yourself

Which is used to send a device-specific command?
- printf
- ioctl
- malloc
- fopen
Show answer

ioctl — ioctl carries device-specific commands.
Match the five concepts

kernel

Protected core
syscall

Numbered service
ioctl

Device command
proc

Virtual filesystem
dmesg

Log buffer

Next lesson: Module loading

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