Linux Kernel Architecture

Purpose

Provide a mental map of the Linux kernel: boot sequence, major subsystems, key data structures, and where to look in source — complementing skills/kernel/kernel-internals with architecture-level navigation for driver and subsystem work.

When to Use

First time exploring linux.git for a feature or bug
Understanding how boot reaches init and driver probe
Tracing a syscall or interrupt through subsystems
Onboarding before skills/kernel-dev/platform-device-model or driver skills

Workflow

1. Boot flow (x86/ARM64 simplified)

firmware/UEFI
├── arch/*/boot — decompress kernel, early setup
├── start_kernel() — mm, scheduler, timers, IRQ subsys
├── rest_init() → kernel_init → run_init_process
└── userspace init (systemd)

Driver module_init / device_initcall run during start_kernel before init.

2. Major subsystems

Subsystem	Path (typical)	Key structs
Scheduler	`kernel/sched/`	`task_struct`, `sched_entity`
Memory	`mm/`	`struct page`, `mm_struct`, `vm_area_struct`
VFS	`fs/`	`inode`, `dentry`, `file`, `super_block`
Block	`block/`	`request_queue`, `gendisk`
Net	`net/`	`sk_buff`, `net_device`
Drivers	`drivers/`	`device`, `device_driver`
Syscalls	`kernel/`, `fs/`, `mm/`	`SYSCALL_DEFINE*`

3. Initcall levels

/* include/linux/init.h — order matters */
early_initcall → core_initcall → postcore_initcall
→ arch_initcall → subsys_initcall → fs_initcall
→ device_initcall → late_initcall

Platform drivers usually register at subsys_initcall or via module_init.

4. Finding code

# Locate symbol
grep -rn "platform_driver_register" drivers/

# Trace config
./scripts/config --state CONFIG_FOO

# File hierarchy docs
ls Documentation/admin-guide/

5. Agent usage

/linux-kernel-architecture Where does page fault handling live and what calls it?

Common Problems

Symptom	Cause	Fix
Driver probes too early	Initcall vs DT ordering	Defer with `deferred_probe`
Symbol missing	Built as module	`modprobe` or built-in `CONFIG_*`
Wrong subsystem	Similar names in `drivers/`	Follow `struct bus_type`
Boot hang	Early printk disabled	`earlyprintk`, `initcall_debug`

Related Skills

skills/kernel/kernel-internals — scheduler, SLUB, VFS depth
skills/kernel-dev/kernel-memory-management — mm/ details
skills/kernel-dev/platform-device-model — driver model
skills/kernel-dev/device-tree — hardware description
skills/low-level-programming/linux-kernel-modules — LKM basics