Process

Kernel Lab 1: Observing Process and VFS Structs Primer on Kernel Data Structures 1. Process & Memory Management (MM) Struct Description Noteworthy Fields task_struct The kernel’s representation of a thread/process. mm (memory space), files (open files), fs (cwd/root), pid, comm (name). mm_struct The descriptor for an entire memory address space. mm_mt (the Maple Tree of VMAs), pgd (page global directory for hardware MMU). vm_area_struct A contiguous range of virtual memory with shared permissions (a VMA). vm_start, vm_end, vm_file (if it’s a memory-mapped file), vm_flags. 2. Virtual File System (VFS) The VFS bridges the gap between user-space file operations (like open() and read()) and the underlying hardware. ...

The Process Address Space — Intro Same flat (single contiguous range) address space model you already have from the article — nothing new conceptually. Key term to lock in: a memory area (this book’s name for what the article calls a VMA) is a permission-tagged interval within that address space. Access outside any valid area, or against an area’s permissions (write to read-only, execute non-executable) → segfault. The list of “what memory areas contain” is just a slightly different cut of the same segments from the article: text, data, bss, stack, shared library mappings, mmap’d files, shared memory, anonymous mappings (malloc). All non-overlapping — every valid address belongs to exactly one area. ...

Virtualizing the CPU — The Process The Core Idea The OS virtualizes the CPU by running one process, stopping it, running another, and so on. Done fast enough, this creates the illusion that many programs run simultaneously on what might be a single CPU core. The abstraction the OS exposes for this is the Process — simply put, a running program. A program is a lifeless set of instructions sitting on disk. A process is that program, brought to life by the OS. ...