Topic Mapping¶

Topic Page	Main Purpose	Related Days
poll and select	Basic readiness-based I/O model	Day15, Day50
epoll	Scalable fd multiplexing and dispatch architecture	Day48-Day51
timerfd	Timer events inside epoll loops	Day48, Day51
signalfd	Graceful shutdown through fd-based signal handling	Day49
eventfd	Lightweight event notification counter	Day52, Day56
fasync and SIGIO	Asynchronous driver notification model	Day52

Event Loop API Reference Pages¶

API Page	Purpose
poll	Basic readiness polling
epoll	Scalable fd event notification
timerfd	Timers as file descriptors
signalfd	Signals as file descriptors
eventfd	Counter-based event notification

Topic	Labs	Notes	API Reference
UNIX Domain Socket	Day53, Day54	UNIX Domain Socket IPC notes	`socketpair`, socket APIs
File Descriptor Passing	Day55	SCM_RIGHTS / FD Passing	`sendmsg`, `recvmsg`, `SCM_RIGHTS`
POSIX Shared Memory	Day56	POSIX Shared Memory IPC	`shm_open`, `mmap`
POSIX Message Queue	Day57	POSIX Message Queue IPC	`mq_open`
POSIX Semaphore	Day58	POSIX Semaphore Sync	`sem_init`, process-shared sync

The Kernel Driver topic has been expanded from a landing page into dedicated review pages and API reference pages.

Topic Page	Main Purpose	Related Days
Character Device Basics	Character device registration and `/dev` interface	Day05, Day06, Day09, Day50
Platform Driver and Device Tree Binding	Device Tree `compatible` matching and platform driver probe	Day08-Day10
GPIO and IRQ Driver	GPIO IRQ, debounce, and deferred processing	Day09, Day11, Day13, Day14
Blocking and Non-blocking I/O	Blocking read, `O_NONBLOCK`, and `-EAGAIN`	Day12, Day18, Day50
Wait Queue and poll Support	Driver `.poll`, wait queues, and epoll readiness	Day12, Day15, Day50, Day51
Driver Control Plane	ioctl and sysfs configuration design	Day16, Day17
fasync and SIGIO	Signal-based async notification and eventfd bridge	Day52

API Page	Purpose
file_operations	Device file operation callbacks
device_create	`/dev` node creation
wait queues	Sleep/wakeup support in drivers
poll_wait	Driver poll/epoll integration
non-blocking I/O	`O_NONBLOCK` and `-EAGAIN` behavior
ioctl	Device control commands
sysfs attributes	Text-based configuration and status
fasync_helper	`SIGIO` async notification

The Subsystem topic has been expanded into handbook-style pages that connect Device Tree, GPIO, hwmon, IIO, Input, and TTY/UART learning paths.

Topic Page	Main Purpose	Related Days
Linux Subsystems	Subsystem-level overview and learning path	Day04-Day44
Device Tree Overlay	Hardware description, overlays, and driver binding	Day04-Day09
GPIO and gpiod	Descriptor-based GPIO lookup and GPIO IRQ flow	Day09, Day11-Day14
hwmon	Standard hardware monitoring sysfs ABI	Day20-Day22
IIO	Sensor channels, triggers, buffers, FIFO, and timestamps	Day33-Day42
Input	Input event reporting through `/dev/input/eventX`	Day43-Day44
TTY and UART	Serial device stack and user-space UART access	Day29, Day31

API Page	Purpose
devm_iio_device_alloc	Allocate an IIO device with managed lifetime
devm_iio_device_register	Register an IIO device
iio_push_to_buffers	Push one scan frame into the IIO buffer
iio_push_to_buffers_with_timestamp	Push one scan frame with timestamp
iio_trigger_poll	Notify an IIO trigger event
devm_input_allocate_device	Allocate an input device
input_register_device	Register an input device
input_set_capability	Declare supported input events
input_report_key	Report a key state
input_sync	Synchronize an input event frame
gpiod_to_irq	Convert a GPIO descriptor to an IRQ number
devm_hwmon_device_register_with_info	Register a hwmon device

Topic	Related Labs	Related Notes	API Reference
Cross Compilation	Day07	Kernel Module Cross Compilation Notes	-
Kernel Module Build	Day05, Day07	Linux Kernel Module	`module_platform_driver()`
Device Tree Overlay Build	Day04, Day09	Device Tree Overlay, Device Tree Naming	`of_device_id`, `platform_driver`
Kernel Version and vermagic	Day05, Day07	Kernel Module Cross Compilation Notes	-