Fix random "ERROR_FILE_NOT_FOUND" when unmounting with absolute path (#40092)

Fix ERROR_FILE_NOT_FOUND when unmounting a vhd with absolute path after the vm timeouts.

Author: chemwolf6922

src/windows/common/WslClient.cpp

@@ -1218,9 +1218,8 @@ int Unmount(_In_ const std::wstring& arg)
     wsl::windows::common::SvcComm service;
     const HRESULT result = wil::ResultFromException([&] { value = service.DetachDisk(disk); });
 
-    // support relative paths in unmount
-    // check is the result is the error code for "file not found" and the path is relative
-    if (result == HRESULT_FROM_WIN32(ERROR_FILE_NOT_FOUND) && PathIsRelative(disk))
+    // Retry with the normalized path to handle relative paths and \\?\ prefix mismatches.
+    if (result == HRESULT_FROM_WIN32(ERROR_FILE_NOT_FOUND))
     {
         // retry dismounting with the absolute path
         const auto absoluteDisk = wsl::windows::common::filesystem::GetFullPath(filesystem::UnquotePath(disk).c_str());

test/windows/MountTests.cpp

@@ -450,6 +450,29 @@ class MountTests
         VERIFY_ARE_EQUAL(LxsstuLaunchWsl(L"--unmount " + absolutePath.wstring()), (DWORD)0);
     }
 
+    TEST_METHOD(AbsolutePathVhdUnmountAfterVMTimeout)
+    {
+        SKIP_UNSUPPORTED_ARM64_MOUNT_TEST();
+        WSL2_TEST_ONLY();
+
+        WslKeepAlive keepAlive;
+
+        VERIFY_ARE_EQUAL(LxsstuLaunchWsl(L"--mount " TEST_MOUNT_VHD L" --vhd --bare"), (DWORD)0);
+
+        const auto disk = GetBlockDeviceInWsl();
+        VERIFY_IS_TRUE(IsBlockDevicePresent(disk));
+
+        WaitForVmTimeout(keepAlive);
+
+        const auto absolutePath = std::filesystem::absolute(TEST_MOUNT_VHD);
+
+        // Validate that the vhd path doesn't start with '\\?'
+        VERIFY_IS_FALSE(absolutePath.wstring().starts_with(L"\\"));
+
+        // Validate the unmounting by absolute path is successful
+        VERIFY_ARE_EQUAL(LxsstuLaunchWsl(L"--unmount " + absolutePath.wstring()), (DWORD)0);
+    }
+
     // Attach a disk, but don't mount it
     TEST_METHOD(TestBareMount)
     {