IOCTLCodes

IOCTLCodes are a mechanism used in Unix-like operating systems to control device-specific operations that are not covered by the standard input/output system calls. IOCTL stands for Input/Output Control. These codes are passed to the ioctl system call, which then directs the kernel to perform a specific action on a device driver. Each device driver defines its own set of IOCTLCodes to manage its unique functionalities.

When a user-space application needs to perform an operation on a device that is not a standard read or write, it typically uses the ioctl system call. The application provides the file descriptor for the device, the IOCTL code, and potentially a pointer to a buffer containing data for the operation or to receive data from the device. The kernel then interprets the IOCTL code and invokes the appropriate handler within the device driver.

IOCTLCodes are often defined as integer constants in header files associated with the specific device or subsystem. They are crucial for interacting with hardware devices, configuring network interfaces, managing file system operations, and performing various other low-level tasks. The specific values of these codes are not standardized across all devices and are determined by the device driver's author. Careful use of ioctl is important, as incorrect codes or data can lead to unexpected behavior or system instability.