Note
Access to this page requires authorization. You can try signing in or changing directories.
Access to this page requires authorization. You can try changing directories.
An instance ID is a string reported by a device's enumerator (its bus driver) and distinguishes a device from other devices of the same type on a computer. An instance ID contains serial number information, if supported by the underlying bus, or some kind of ___location information. The string cannot contain any "\" characters or any other character disallowed in a response to a IRP_MN_QUERY_ID request; otherwise, the generic format of the string is bus-specific. The number of characters of an instance ID, excluding a NULL-terminator, must be less than MAX_DEVICE_ID_LEN. In addition, the instance ID is another input into the creation of the device instance ID, along with a device ID, and the maximum possible length of a device instance ID is MAX_DEVICE_ID_LEN. This requires that the length of the instance ID be enough less than MAX_DEVICE_ID_LEN that the device instance ID can be created as a string with length less than MAX_DEVICE_ID_LEN.
The UniqueID member of the DEVICE_CAPABILITIES structure for a device indicates if a bus-supplied instance ID is unique across the system, as follows:
If UniqueID is FALSE, the bus-supplied instance ID for a device is unique only to the device's bus. The Plug and Play (PnP) manager modifies the bus-supplied instance ID, and combines it with the corresponding device ID, to create a device instance ID that is unique in the system.
If UniqueID is TRUE, the device instance ID, formed from the bus-supplied device ID and instance ID, uniquely identifies a device in the system.
An instance ID is persistent across system restarts.
The PnP manager queries this string from the device's bus driver using an IRP_MN_QUERY_ID request with the Parameters.QueryId.IdType field set to BusQueryInstanceID.