What are the benefits and challenges of using Windows Service Control Manager (SCM) for user mode services?

1 Benefits of SCM

SCM provides several advantages for user mode services, such as the ability to specify dependencies, security context, and recovery actions. It also handles communication between the service and the operating system, such as reporting the status, receiving commands, and logging events. Furthermore, SCM enables you to start, stop, pause, resume, and configure your service remotely, using tools like the Services snap-in, the sc command, or the PowerShell cmdlets. Additionally, it supports the automatic or delayed start of your service, depending on the system state and other conditions.

2 Challenges of SCM

SCM poses some challenges for user mode services, such as the need to follow a specific programming model, the limitations on the service, and the potential errors, failures, and security risks. Additionally, it adds complexity to the development, testing, and deployment process, such as the need to register, install, and uninstall the service, and to debug it using tools like the Event Viewer, the DebugView, or the WinDbg.

3 Creating a user mode service

To create a user mode service, you must define the service name, display name, description, and type. Additionally, you must implement the service main function and the service control handler function, and register the service main function with the StartServiceCtrlDispatcher function. Furthermore, you must write the code for your service logic, such as initializing, performing, and cleaning up the tasks of your service. Finally, use the SetServiceStatus function to report the status of your service to SCM, such as SERVICE_START_PENDING, SERVICE_RUNNING, or SERVICE_STOPPED.

4 Installing a user mode service

To install a user mode service, you must compile your service code into an executable file, such as MyService.exe, and copy it to a suitable location, such as C:\Program Files\MyService. Then, use the CreateService function or the sc create command to create a service entry in the registry, specifying the service name, display name, description, type, and path to the executable file. Optionally, you can use the ChangeServiceConfig2 function or the sc description command to set the description of your service, which will appear in the Services snap-in or the sc query command. Additionally, you can use the ChangeServiceConfig function or the sc config command to configure the dependencies, security context, and recovery actions of your service, such as the services that your service depends on, the account that your service runs under, and the actions that SCM should take if your service fails.

5 Debugging a user mode service

To debug a user mode service, you must use the Event Viewer, DebugView, or OutputDebugString function to view messages and events generated by the service or SCM. Additionally, you should use WinDbg, Visual Studio, or the Attach to Process feature to attach a debugger to the process hosting the service and set breakpoints, examine variables, and step through the code. Lastly, you can use the Services snap-in, sc command, or PowerShell cmdlets to control the startup, shutdown, and configuration of the service.