Day51 - Timer-Based Pollable Event Driver

Objective

Extend the Day50 pollable character driver into a timer-driven asynchronous event framework.

Features implemented:

• delayed_work periodic event source
• timer start/stop commands
• manual trigger events
• runtime statistics
• queue overflow tracking
• sysfs runtime status
• epoll integration

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Lab 1 - Refactor Event Generation Helper

Goal

Move event generation into a shared helper function.

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Implementation

Create shared helper:

static int mypoll_generate_event(struct mypoll_dev *mydev,
                                 enum mypoll_event_source source)

Responsibilities:

• generate sequence number
• queue push
• overflow handling
• statistics update
• wait queue wakeup

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Lab 2 - Add delayed_work Timer Event Source

Goal

Generate periodic events inside the driver.

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Device Structure

Add:

struct delayed_work event_work;
unsigned int event_interval_ms;
bool event_running;

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Work Handler

static void mypoll_event_work_handler(struct work_struct *work)
{
    ...
}

Responsibilities:

• generate timer event
• re-schedule delayed_work

---

Initialization

INIT_DELAYED_WORK(&mydev->event_work,
                  mypoll_event_work_handler);

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Cleanup

cancel_delayed_work_sync(&mydev->event_work);

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Lab 3 - Add Control Commands

Goal

Control timer behavior from userspace.

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Supported Commands

Command	Description
start	Start periodic timer
stop	Stop periodic timer
trigger	Generate one manual event
reset_stats	Clear statistics
show_stats	Print runtime statistics

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Example

echo start > /dev/mypoll
echo stop > /dev/mypoll
echo trigger > /dev/mypoll

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Lab 4 - Add Event Source Information

Goal

Differentiate manual and timer events.

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Event Source Enum

enum mypoll_event_source {
    MYPOLL_EVENT_SOURCE_MANUAL = 0,
    MYPOLL_EVENT_SOURCE_TIMER,
};

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Event Structure

struct mypoll_event {
    u32 sequence;
    enum mypoll_event_source source;
};

---

Userspace Output

event=35 source=manual
event=36 source=timer

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Lab 5 - Add Runtime Statistics

Goal

Track runtime event behavior.

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Statistics Structure

struct mypoll_stats {
    u32 events_generated;
    u32 events_dropped;
    u32 events_manual;
    u32 events_timer;
};

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Overflow Policy

When queue is full:

queue full
    ↓
drop new event
    ↓
increment dropped counter

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Lab 6 - Add sysfs Runtime Status

Goal

Expose runtime driver state through sysfs.

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sysfs Node

/sys/class/mypoll/mypoll/stats

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sysfs Attribute

static DEVICE_ATTR_RO(stats);

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Example Output

event_sequence=83
generated=83
dropped=174
manual_triggered=1
timer_triggered=82
queue_depth=0
timer_running=0

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Lab 7 - epoll Integration

Goal

Verify that timer events work with epoll.

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Userspace Flow

epoll_wait()
    ↓
EPOLLIN
    ↓
read()

---

Result

Timer-generated events successfully wake epoll waiters.

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Lab 8 - Python Integration Test

Goal

Automate runtime validation.

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Tested Features

• manual trigger
• timer events
• timer stop
• epoll wakeup
• queue overflow
• reset statistics
• sysfs stats

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Example Output

===== Test 5: Queue overflow should increase dropped counter =====
[OK] Overflow observed: dropped=1, queue_depth=16

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Final Result

The driver evolved from a simple pollable character device into a reusable asynchronous event framework.

Key concepts learned:

• delayed_work scheduling
• asynchronous event flow
• runtime observability
• queue overflow handling
• epoll integration
• sysfs runtime statistics