Windows Kernel I/O Drivers
The Windows I/O subsystem is a critical component of the operating system, responsible for managing all input and output operations between hardware devices and user-mode applications. Kernel-mode drivers are the software components that interact directly with the hardware, translating high-level I/O requests from the system into low-level commands that the hardware can understand.
Key Concepts
- I/O Request Packets (IRPs): The primary mechanism for communication between the I/O manager, drivers, and file system. IRPs encapsulate all information needed for an I/O operation.
- Driver Object: A data structure that represents a loaded driver and contains pointers to the driver's dispatch routines.
- Device Object: A data structure that represents a physical or logical device managed by a driver.
- Dispatch Routines: Functions within a driver that handle specific I/O operations (e.g.,
IRP_MJ_READ,IRP_MJ_WRITE,IRP_MJ_DEVICE_CONTROL). - I/O Manager: A kernel component that manages I/O operations, queues IRPs, and dispatches them to the appropriate drivers.
- WDM (Windows Driver Model) and WDF (Windows Driver Frameworks): Frameworks that provide a structured approach to driver development. WDM is the foundational model, while WDF (including UMDF and KMDF) offers a more object-oriented and simplified development experience.
Driver Types
Drivers can be categorized based on their function:
- Bus Drivers: Control a particular type of bus (e.g., PCI, USB).
- Class Drivers: Provide a common interface for a class of devices (e.g., disk drives, printers).
- Function Drivers: The primary driver for a specific device.
- Filter Drivers: Intercept I/O requests to modify or augment functionality.
- Port Drivers: Control a specific type of I/O port.
Driver Development
Developing kernel-mode drivers requires a deep understanding of the Windows operating system internals, C programming, and specific driver frameworks. Tools like the Windows Driver Kit (WDK) are essential for building, debugging, and testing drivers.
Common Driver Functions
- Handling I/O requests and creating/completing IRPs.
- Interacting with hardware registers.
- Managing device power states.
- Registering for Plug and Play and Power Management events.
Key Kernel Functions for Drivers
IoCreateDevice: Creates a device object.
IoCreateCompletionRoutine: Sets up a completion routine for an IRP.
IoQueueIoWorkItem: Queues an I/O work item for asynchronous processing.
WdfDriverCreate (KMDF): Initializes a kernel-mode driver object.
WdfDeviceCreate (KMDF): Creates a framework device object.
IRP_MJ_READ, IRP_MJ_WRITE, IRP_MJ_DEVICE_CONTROL: Major IRP codes handled by dispatch routines.