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The Completely Fair Scheduler (CFS) governs CPU allocation in the Linux kernel by tracking virtual execution time. Rather than relying on fixed time slices, CFS maintains a running average of how long each schedulable unit has consumed processor resources. The system continuously selects the entity with the lowest accumulated virtual runtime fo ...

This example demonstrates how to implement a GPIO-controlled LED driver that ensures only one user process can access the LED at a time using a counting semaphore initialized to 1 (binary semaphore). The semaphore is acquired in the open() handler and released in the release() handler, effectively serializign access across multiple processes. D ...

The Linux kernel employs the struct irq_chip abstraction to represent interrupt controller hardware. Since different processor architectures manage interrupts uniquely, this structure encapsulates callback functon pointers directed at the underlying hardware control logic. Key operations such as enabling, masking, and configuring affinity are r ...

System Call: This is the most common method. A user-space program requests the kernel to perform a specific action through the system call interface (e.g., open, read, write, fork). System calls serve as the bridge between user-space and kernel-space, allowing user programs to request kernel services. Interrupts: Interrupts include soft interru ...

Understanding the select System Call The select system call provides synchronous I/O multiplexing, allowing a program to monitor multiple file descriptors for readiness. This analysis explores its internal implementation in the Linux kernel. User Interface The select API is defined as follows: #include <sys/select.h> int select(int maxfd ...

The epoll(2) mechanism in the Linux kernel provides an efficeint I/O event notification system. This analysis is based on kernel version 5.0.18 and explores its internal structures, system calls, and handling of ready events. Core Data Structures The primary data structure representing an epoll instance is struct eventpoll: struct eventpoll { ...

Virtual File System Abstraction Linux accommodates a wide variety of storage formats, including ext4, XFS, FAT, NTFS, and iso9660. Despite the differences in on-disk structures and underlying hardware, the operating system presents a unified directory tree to applications. Operations like directory listing, reading, and writing behave identi ...

Background Embedded development often requires network connectivity between the target board and host PC. When the target device lacks a native RJ45 Ethernet port, USB-to-Ethernet adapters provide a practical solution. This guide covers the kernel configuration needed to enable USB networking support. Hardware Prerequisites A USB-to-Ethernet do ...