| Platform SDK: Fax Services |
The fax service calls the fax service provider's FAX_LINECALLBACK function to inform the service provider when an end user enables or disables the sending or receiving of faxes on a virtual fax device. The fax service provider registers the callback function by passing its address when the fax service calls the FaxDevInitialize function.
The fax service calls the FaxDevInitialize function using the following values.
| Parameter | Value |
|---|---|
| FaxHandle | NULL |
| hDevice | The identifier of the virtual fax device. |
| dwMessage | LINE_DEVSPECIFIC |
| dwInstance | Zero |
| dwParam1 | The fax service generates a value for this parameter. If the virtual fax device is enabled to receive faxes, this parameter has a nonzero value. If fax reception is disabled, this parameter is equal to zero. |
| dwParam2 | The fax service generates a value for this parameter. If the virtual fax device is enabled to send faxes, this parameter has a nonzero value. If fax sending is disabled, this parameter is equal to zero. |
| dwParam3 | Zero |
The fax service calls FAX_LINECALLBACK multiple times, once for each virtual device the fax service provider supports, even if the status of only one virtual device changes.
For more information about identifiers for virtual fax devices, see the description of the DeviceIdPrefix parameter of the FaxDevVirtualDeviceCreation function.
For more information about enabling or disabling the transmission and reception of faxes on a fax device, see FaxEnumPorts, FaxGetPort, FaxSetPort, FAX_PORT_INFO, and Fax Device Management in the Fax Service Client API documentation.