IO Manager

Overview

The IO Manager is the kernel component responsible for managing all I/O operations in Windows. It provides the infrastructure for device drivers, handles I/O request packets (IRPs), and implements the Windows I/O model.

Key responsibilities

• Creation and management of device objects.
• Dispatching IRPs to appropriate driver routines.
• Synchronizing access to devices.
• Providing I/O completion mechanisms.
• Supporting plug‑and‑play, power management, and security checks.

Functions

Below are the most commonly used IO Manager functions. Click a function name to view its detailed documentation.

Structures

• DEVICE_OBJECT – Represents a device created by a driver.
• IRP – I/O request packet that describes an I/O operation.
• IO_STACK_LOCATION – Stack frame that driver routines use to access parameters.
• FILE_OBJECT – Represents an open instance of a file or device.

Constants & Enumerations

typedef enum _IO_ALLOCATION_ACTION {
    KeepObject,
    DeallocateObject,
    DeallocateObjectKeepRegisters
} IO_ALLOCATION_ACTION;

#define IO_NO_INCREMENT 0
#define IO_NO_PARAMETERS 0x00000000

Remarks

The IO Manager interacts heavily with the Plug and Play (PnP) and Power Manager subsystems. When developing a kernel‑mode driver, you must follow the IRP processing rules and correctly set the Status field before completing the request.

Best practices

1. Validate all input buffers before accessing them.
2. Use IoMarkIrpPending when an operation will be completed asynchronously.
3. Always set the appropriate IRP_MJ_* major function codes during driver initialization.
4. Release any allocated resources in the driver’s Unload routine.

See also

• Plug and Play (PnP)
• Power Manager
• Windows Driver Development Guide