| Platform SDK: Hardware |
Applications, including services, can register to receive notification of device events. For example, a catalog service can receive notice of volumes being mounted or dismounted so it can adjust the paths to files on the volume. The system notifies an application that a device event has occurred by sending the application a WM_DEVICECHANGE message. The system notifies a service that a device event has occurred by invoking the service's event handler function, HandlerEx.
To receive device event notices, call the RegisterDeviceNotification function with a DEV_BROADCAST_HANDLE structure. Be sure to set the dbch_handle member to the device handle obtained from the CreateFile function. Also, set the dbch_devicetype member to DBT_DEVTYP_HANDLE. The function returns a device notification handle. Note that this is not the same as the volume handle.
When your application receives notification, if the event type is DBT_CUSTOMEVENT, you may have received one of the device events defined in IoEvent.h. To determine if one of these events has occurred, use the following steps.
| Device Event GUID | Meaning |
|---|---|
| GUID_IO_VOLUME_CHANGE | The volume label has changed. |
| GUID_IO_VOLUME_DISMOUNT | An attempt to dismount the volume is in progress. You should close all handles to files and directories on the volume. GUID_IO_VOLUME_DISMOUNT will not necessarily be preceded by a GUID_IO_VOLUME_LOCK notice. |
| GUID_IO_VOLUME_DISMOUNT_FAILED | An attempt to dismount a volume failed. This often happens because another process failed to respond to a GUID_IO_VOLUME_DISMOUNT notice by closing its outstanding handles. Because the dismount failed, you may reopen any handles to the affected volume. |
| GUID_IO_VOLUME_LOCK | Another process is attempting to lock the volume. You should close all handles to files and directories on the volume. |
| GUID_IO_VOLUME_LOCK_FAILED | An attempt to lock a volume failed. This often happens because another process failed to respond to a GUID_IO_VOLUME_LOCK notice by closing its outstanding handles. Because the lock failed, you may reopen any handles to the affected volume. |
| GUID_IO_VOLUME_MOUNT | The volume has been mounted by another process. You may open one or more handles to it. |
| GUID_IO_VOLUME_UNLOCK | The volume has been unlocked by another process. You may open one or more handles to it. |
The GUID_IO_VOLUME_DISMOUNT and GUID_IO_VOLUME_DISMOUNT_FAILED events are related, as are the GUID_IO_VOLUME_LOCK and GUID_IO_VOLUME_LOCK_FAILED event. The GUID_IO_VOLUME_DISMOUNT and GUID_IO_VOLUME_LOCK events indicate that an operation is being attempted. You should act on the event notification, and record the action taken. The GUID_IO_VOLUME_DISMOUNT_FAILED and GUID_IO_VOLUME_LOCK_FAILED events indicate that the attempted operation failed. You may then use your record to undo the actions you made in response to the operation.
The dbch_hdevnotify member of the DEV_BROADCAST_HANDLE structure indicates the affected device. Note that this is the device notification handle returned by RegisterDeviceNotification, not a volume handle. To perform operations on the volume, map this handle to the corresponding volume handle.