Expose the VM ID inside user distros (#13212)

* Add --vm-id to wslinfo usage string

* Pass the VM id to init

This change ensures that we pass the vm id to an
instances init. The id is then set as an environment
variable and can be accessed at runtime.

* Expose VM id to wslinfo

Add a new argument --vm-id to wslinfo so that
the caller can retrieve the VM id by calling the
binary.

Although it is an environment variable, it can be useful
here too to save additional string parsing from the caller.

localization/strings/en-US/Resources.resw

@@ -321,6 +321,9 @@ Please enable the "Windows Subsystem for Linux" optional component to use WSL1.<
     --msal-proxy-path
         Display the path to the MSAL proxy application.
 
+    --vm-id
+        Display the WSL VM ID.
+
     --version
         Display the version of the WSL package.
 
@@ -328,6 +331,7 @@ Please enable the "Windows Subsystem for Linux" optional component to use WSL1.<
         Do not print a newline.</value>
     <comment>{Locked="--networking-mode
 "}{Locked="--msal-proxy-path
+"}{Locked="--vm-id
 "}{Locked="--version
 "}Command line arguments, file names and string inserts should not be translated</comment>
   </data>

src/linux/init/main.cpp

@@ -2582,7 +2582,7 @@ void ProcessLaunchInitMessage(
             DISTRO_PATH,
             enableGuiApps,
             Config,
-            nullptr,
+            wsl::shared::string::FromSpan(Buffer, Message->VmIdOffset),
             wsl::shared::string::FromSpan(Buffer, Message->DistributionNameOffset),
             nullptr,
             wsl::shared::string::FromSpan(Buffer, Message->InstallPathOffset),

src/linux/init/wslinfo.cpp

@@ -23,12 +23,14 @@ Abstract:
 #include "defs.h"
 #include "Localization.h"
 #include "CommandLine.h"
+#include "../../shared/inc/lxinitshared.h"
 
 enum class WslInfoMode
 {
     GetNetworkingMode,
     MsalProxyPath,
-    WslVersion
+    WslVersion,
+    VMId
 };
 
 int WslInfoEntry(int Argc, char* Argv[])
@@ -65,6 +67,7 @@ Return Value:
     parser.AddArgument(UniqueSetValue<WslInfoMode, WslInfoMode::MsalProxyPath>{Mode, Usage}, WSLINFO_MSAL_PROXY_PATH);
     parser.AddArgument(UniqueSetValue<WslInfoMode, WslInfoMode::WslVersion>{Mode, Usage}, WSLINFO_WSL_VERSION);
     parser.AddArgument(UniqueSetValue<WslInfoMode, WslInfoMode::WslVersion>{Mode, Usage}, WSLINFO_WSL_VERSION_LEGACY);
+    parser.AddArgument(UniqueSetValue<WslInfoMode, WslInfoMode::VMId>{Mode, Usage}, WSLINFO_WSL_VMID);
     parser.AddArgument(NoOp{}, WSLINFO_WSL_HELP);
     parser.AddArgument(noNewLine, nullptr, WSLINFO_NO_NEWLINE);
 
@@ -144,6 +147,22 @@ Return Value:
     {
         std::cout << WSL_PACKAGE_VERSION;
     }
+    else if (Mode.value() == WslInfoMode::VMId)
+    {
+        auto value = UtilGetEnvironmentVariable(LX_WSL2_VM_ID_ENV);
+        if (value.empty())
+        {
+            std::cerr << Localization::MessageNoValueFound() << "\n";
+            return 1;
+        }
+
+        std::cout << value;
+    }
+    else
+    {
+        assert(false && "Unknown WslInfoMode");
+        return 1;
+    }
 
     if (!noNewLine)
     {

src/linux/init/wslinfo.h

@@ -20,6 +20,7 @@ Abstract:
 #define WSLINFO_NETWORKING_MODE "--networking-mode"
 #define WSLINFO_WSL_VERSION "--version"
 #define WSLINFO_WSL_VERSION_LEGACY "--wsl-version"
+#define WSLINFO_WSL_VMID "--vm-id"
 #define WSLINFO_WSL_HELP "--help"
 #define WSLINFO_NO_NEWLINE 'n'
 

test/windows/UnitTests.cpp

@@ -842,6 +842,18 @@ class UnitTests
                 L"Invalid command line argument: --invalid\nPlease use 'wslinfo --help' to get a list of supported "
                 L"arguments.\n");
         }
+
+        if (LxsstuVmMode())
+        {
+            // Get the VM ID from the distro and validate that it not null.
+            auto [vmId, vmIdErr] = LxsstuLaunchWslAndCaptureOutput(L"env | grep 'WSL2_VM_ID' | awk -F= '{print $2}'");
+            VERIFY_ARE_NOT_EQUAL(vmId, L"");
+
+            // Ensure that the response from wslinfo matches the VM id from the distros environment
+            auto [out, err] = LxsstuLaunchWslAndCaptureOutput(L"wslinfo --vm-id");
+            VERIFY_ARE_EQUAL(out, std::format(L"{}", vmId));
+            VERIFY_ARE_EQUAL(err, L"");
+        }
     }
 
     TEST_METHOD(WslPath)