Implement the WSLC plugin API

msipackage/package.wix.in

@@ -353,6 +353,14 @@
                     </RegistryKey>
                 </RegistryKey>
 
+                <!-- IWSLCPluginNotifier-->
+                <RegistryKey Root="HKCR" Key="Interface\{F3E6D5B2-1D40-4E8B-9C39-7A45D1C0F8A2}">
+                    <RegistryValue Value="IWSLCPluginNotifier" Type="string" />
+                    <RegistryKey Key="ProxyStubClsid32">
+                        <RegistryValue Value="{4EA0C6DD-E9FF-48E7-994E-13A31D10DC60}" Type="string" />
+                    </RegistryKey>
+                </RegistryKey>
+
                 <File Id="wslcsession.exe" Source="${BIN}/wslcsession.exe" />
             </Component>
             <Component Id="wslg" Guid="F0C8D6BA-1502-41E7-BF72-D93DFA134731" UninstallWhenSuperseded="yes" DisableRegistryReflection="yes" Bitness="always64">

src/windows/inc/WslPluginApi.h

@@ -26,6 +26,9 @@ extern "C" {
 #define WSLPLUGINAPI_ENTRYPOINTV1 WSLPluginAPIV1_EntryPoint
 #define WSL_E_PLUGIN_REQUIRES_UPDATE MAKE_HRESULT(SEVERITY_ERROR, FACILITY_ITF, 0x032A)
 
+// Maximum size for mount points returned by WSLCPluginAPI_MountFolder. This includes the null terminator.
+#define WSLC_MOUNTPOINT_LENGTH 256
+
 #define WSL_PLUGIN_REQUIRE_VERSION(_Major, _Minor, _Revision, Api) \
     if (Api->Version.Major < (_Major) || (Api->Version.Major == (_Major) && Api->Version.Minor < (_Minor)) || \
         (Api->Version.Major == (_Major) && Api->Version.Minor == (_Minor) && Api->Version.Revision < (_Revision))) \
@@ -85,13 +88,94 @@ struct WslOfflineDistributionInformation
     LPCWSTR Version;           // Distribution version. Introduced in 2.4.4
 };
 
+// Identifies a WSLC session inside the WSLC plugin API. Distinct from WSLSessionId.
+typedef DWORD WSLCSessionId;
+
+// Information about a WSLC session passed to plugin notifications.
+struct WSLCSessionInformation
+{
+    WSLCSessionId SessionId;
+    LPCWSTR DisplayName;
+    DWORD ApplicationPid;
+    HANDLE UserToken;
+    PSID UserSid;
+};
+
+// Opaque handle to a WSLC process created via WSLCPluginAPI_CreateProcess.
+// Must be released with WSLCPluginAPI_ReleaseProcess.
+typedef void* WSLCProcessHandle;
+
+typedef enum _WSLCProcessFd
+{
+    WSLCProcessFdStdin = 0,
+    WSLCProcessFdStdout = 1,
+    WSLCProcessFdStderr = 2
+} WSLCProcessFd;
+
 // Create plan9 mount between Windows & Linux
 typedef HRESULT (*WSLPluginAPI_MountFolder)(WSLSessionId Session, LPCWSTR WindowsPath, LPCWSTR LinuxPath, BOOL ReadOnly, LPCWSTR Name);
 
 // Execute a program in the root namespace.
 // On success, 'Socket' is connected to stdin & stdout (stderr goes to dmesg) // 'Arguments' is expected to be NULL terminated
 typedef HRESULT (*WSLPluginAPI_ExecuteBinary)(WSLSessionId Session, LPCSTR Path, LPCSTR* Arguments, SOCKET* Socket);
 
+//
+// WSLC plugin hooks.
+//
+
+// Called when a WSLC session is created. Returning an error prevents the session creation.
+typedef HRESULT (*WSLPluginAPI_OnSessionCreated)(const struct WSLCSessionInformation* Session);
+
+// Called when a WSLC session is about to stop. Errors are ignored.
+typedef HRESULT (*WSLPluginAPI_OnSessionStopping)(const struct WSLCSessionInformation* Session);
+
+// Called when a container starts. Returning an error prevents the container creation.
+// 'InspectContainer' is a JSON document that follows the wslc_schema::InspectContainer format.
+typedef HRESULT (*WSLPluginAPI_ContainerStarted)(const struct WSLCSessionInformation* Session, LPCSTR InspectContainer);
+
+// Called when a container is about to stop. 'ContainerId' is the container identifier. Errors are ignored.
+typedef HRESULT (*WSLPluginAPI_ContainerStopping)(const struct WSLCSessionInformation* Session, LPCSTR ContainerId);
+
+// Called when an image is created (either pulled, or imported). Errors are ignored.
+// 'InspectImage' is a JSON document that follows the wslc_schema::InspectImage format.
+// N.B. This callback is currently only invoked when images are pulled or imported. Images created via load or build are not reported.
+typedef HRESULT (*WSLPluginAPI_ImageCreated)(const struct WSLCSessionInformation* Session, LPCSTR InspectImage);
+
+// Called when an image is deleted. 'ImageId' is the deleted image identifier. Errors are ignored.
+typedef HRESULT (*WSLPluginAPI_ImageDeleted)(const struct WSLCSessionInformation* Session, LPCSTR ImageId);
+
+//
+// WSLC plugin API calls.
+//
+
+// Mount a Windows folder into the WSLC session VM. The mount path is returned via 'Mountpoint'.
+// 'Mountpoint' must point to a buffer of at least WSLC_MOUNTPOINT_LENGTH chars, including the null terminator.
+typedef HRESULT (*WSLCPluginAPI_MountFolder)(WSLCSessionId Session, LPCWSTR WindowsPath, BOOL ReadOnly, LPCWSTR Name, LPSTR Mountpoint);
+
+// Unmount a folder previously mounted via WSLCPluginAPI_MountFolder.
+typedef HRESULT (*WSLCPluginAPI_UnmountFolder)(WSLCSessionId Session, LPCSTR Mountpoint);
+
+// Create a process in the WSLC session's root namespace.
+// 'Arguments' and 'Env' are NULL-terminated arrays. 'Env' may be NULL.
+// 'Errno' is optional and receives the errno value if the process creation fails.
+// On success, 'Process' receives an opaque handle that must be released with WSLCPluginAPI_ReleaseProcess.
+typedef HRESULT (*WSLCPluginAPI_CreateProcess)(
+    WSLCSessionId Session, LPCSTR Executable, LPCSTR* Arguments, LPCSTR* Env, WSLCProcessHandle* Process, int* Errno);
+
+// Get a stdio handle from a WSLC process. The caller takes ownership and must close it with CloseHandle().
+typedef HRESULT (*WSLCPluginAPI_ProcessGetFd)(WSLCProcessHandle Process, WSLCProcessFd Fd, HANDLE* Handle);
+
+// Get the exit event for a WSLC process. Signaled when the process exits.
+// The caller takes ownership and must close it with CloseHandle().
+typedef HRESULT (*WSLCPluginAPI_ProcessGetExitEvent)(WSLCProcessHandle Process, HANDLE* ExitEvent);
+
+// Get the exit code of a WSLC process. The process must have exited.
+typedef HRESULT (*WSLCPluginAPI_ProcessGetExitCode)(WSLCProcessHandle Process, int* ExitCode);
+
+// Release a WSLC process handle. All outstanding handles obtained via
+// WSLCPluginAPI_ProcessGetFd/GetExitEvent must be closed before calling this.
+typedef void (*WSLCPluginAPI_ReleaseProcess)(WSLCProcessHandle Process);
+
 // Execute a program in a user distribution
 // On success, 'Socket' is connected to stdin & stdout (stderr goes to dmesg) // 'Arguments' is expected to be NULL terminated
 typedef HRESULT (*WSLPluginAPI_ExecuteBinaryInDistribution)(WSLSessionId Session, const GUID* Distribution, LPCSTR Path, LPCSTR* Arguments, SOCKET* Socket);
@@ -132,6 +216,14 @@ struct WSLPluginHooksV1
     WSLPluginAPI_OnDistributionStopping OnDistributionStopping;
     WSLPluginAPI_OnDistributionRegistered OnDistributionRegistered;   // Introduced in 2.1.2
     WSLPluginAPI_OnDistributionRegistered OnDistributionUnregistered; // Introduced in 2.1.2
+
+    // WSLC hooks. Plugins compiled against older headers leave these zero-initialized.
+    WSLPluginAPI_OnSessionCreated OnSessionCreated;
+    WSLPluginAPI_OnSessionStopping OnSessionStopping;
+    WSLPluginAPI_ContainerStarted ContainerStarted;
+    WSLPluginAPI_ContainerStopping ContainerStopping;
+    WSLPluginAPI_ImageCreated ImageCreated;
+    WSLPluginAPI_ImageDeleted ImageDeleted;
 };
 
 struct WSLPluginAPIV1
@@ -141,10 +233,19 @@ struct WSLPluginAPIV1
     WSLPluginAPI_ExecuteBinary ExecuteBinary;
     WSLPluginAPI_PluginError PluginError;
     WSLPluginAPI_ExecuteBinaryInDistribution ExecuteBinaryInDistribution; // Introduced in 2.1.2
+
+    // WSLC API calls.
+    WSLCPluginAPI_MountFolder WSLCMountFolder;                 // Introduced in 2.9.0
+    WSLCPluginAPI_UnmountFolder WSLCUnmountFolder;             // Introduced in 2.9.0
+    WSLCPluginAPI_CreateProcess WSLCCreateProcess;             // Introduced in 2.9.0
+    WSLCPluginAPI_ProcessGetFd WSLCProcessGetFd;               // Introduced in 2.9.0
+    WSLCPluginAPI_ProcessGetExitEvent WSLCProcessGetExitEvent; // Introduced in 2.9.0
+    WSLCPluginAPI_ProcessGetExitCode WSLCProcessGetExitCode;   // Introduced in 2.9.0
+    WSLCPluginAPI_ReleaseProcess WSLCReleaseProcess;           // Introduced in 2.9.0
 };
 
 typedef HRESULT (*WSLPluginAPI_EntryPointV1)(const struct WSLPluginAPIV1* Api, struct WSLPluginHooksV1* Hooks);
 
 #ifdef __cplusplus
 }
-#endif
+#endif

src/windows/service/exe/CMakeLists.txt

@@ -23,6 +23,7 @@ set(SOURCES
     HcsVirtualMachine.cpp
     WSLCSessionManager.cpp
     WSLCSessionManagerFactory.cpp
+    WSLCPluginNotifier.cpp
     main.rc
     ${CMAKE_CURRENT_BINARY_DIR}/../mc/${TARGET_PLATFORM}/${CMAKE_BUILD_TYPE}/wsleventschema.rc
     application.manifest)
@@ -53,7 +54,8 @@ set(HEADERS
     WslCoreVm.h
     HcsVirtualMachine.h
     WSLCSessionManager.h
-    WSLCSessionManagerFactory.h)
+    WSLCSessionManagerFactory.h
+    WSLCPluginNotifier.h)
 
 add_executable(wslservice ${SOURCES} ${HEADERS})
 add_dependencies(wslservice wslserviceidl wslservicemc)

src/windows/service/exe/LxssUserSessionFactory.cpp

@@ -30,7 +30,7 @@ srwlock g_sessionLock;
 std::optional<std::vector<std::shared_ptr<LxssUserSessionImpl>>> g_sessions =
     std::make_optional<std::vector<std::shared_ptr<LxssUserSessionImpl>>>();
 
-std::optional<wsl::windows::service::PluginManager> g_pluginManager;
+extern wsl::windows::service::PluginManager g_pluginManager;
 
 extern unique_event g_networkingReady;
 extern bool g_lxcoreInitialized;
@@ -53,9 +53,6 @@ void ClearSessionsAndBlockNewInstancesLockHeld(std::optional<std::vector<std::sh
 
         sessions.reset();
     }
-
-    // Unload plugins
-    g_pluginManager.reset();
 }
 
 void ClearSessionsAndBlockNewInstances()
@@ -84,12 +81,6 @@ void SetSessionPolicy(_In_ bool enabled)
         {
             g_sessions = std::make_optional<std::vector<std::shared_ptr<LxssUserSessionImpl>>>();
         }
-
-        if (!g_pluginManager.has_value())
-        {
-            g_pluginManager.emplace();
-            g_pluginManager->LoadPlugins();
-        }
     }
     else
     {
@@ -236,7 +227,7 @@ std::weak_ptr<LxssUserSessionImpl> CreateInstanceForCurrentUser()
 
         if (!userSession)
         {
-            userSession.reset(new LxssUserSessionImpl(tokenInfo->User.Sid, sessionId, *g_pluginManager));
+            userSession.reset(new LxssUserSessionImpl(tokenInfo->User.Sid, sessionId, g_pluginManager));
             g_sessions->emplace_back(userSession);
         }
     }