virtiofs: impersonate Windows users for host filesystem access

Cargo.lock

@@ -10635,6 +10635,7 @@ dependencies = [
  "tempfile",
  "test_with_tracing",
  "thiserror 2.0.16",
+ "tracelimit",
  "tracing",
  "virtio",
  "virtio_resources",
@@ -11386,6 +11387,7 @@ dependencies = [
  "vmgs_resources",
  "vmm_test_igvm_agent",
  "vmm_test_macros",
+ "windows-sys 0.61.0",
  "x509-cert",
  "x86defs",
  "zerocopy",

Guide/src/reference/openvmm/management/grpc.md

@@ -84,6 +84,19 @@ If a write fails, OpenVMM logs the error and disconnects the file backend.
 Further console output is discarded; the backend does not automatically retry
 or reopen the file.
 
+## Passing handles on Windows
+
+Some API fields reference OS handles by name. For example,
+`VirtioFs.WindowsOptions.user_token_name` names an access token that virtio-fs
+impersonates for host file access.
+
+Clients register these handles over the same socket using the
+[resource-passing protocol]. Because Windows Unix sockets cannot carry handles,
+the client duplicates each handle into the OpenVMM process with
+`DuplicateHandle`, which requires `PROCESS_DUP_HANDLE` access to it, and sends
+the handle value under a name. OpenVMM makes its own duplicate; the client then
+closes its copy in OpenVMM.
+
 ## Graceful guest shutdown
 
 `ShutdownVM` requests a cooperative guest power-off, non-forced by default.
@@ -246,3 +259,4 @@ When editing `vmservice.proto`, follow the
 [Protocol Buffers enum conventions](../../../dev_guide/contrib/code.md#protocol-buffers-enums).
 
 [`vmservice.proto`]: https://github.com/microsoft/openvmm/blob/main/openvmm/openvmm_ttrpc_vmservice/src/vmservice.proto
+[resource-passing protocol]: https://github.com/microsoft/openvmm/blob/main/openvmm/openvmm_ttrpc_vmservice/src/resource_passing.md

openvmm/openvmm_entry/Cargo.toml

@@ -118,6 +118,7 @@ win_etw_tracing.workspace = true
 workspace = true
 features = [
   "Win32_Foundation",
+  "Win32_Security",
   "Win32_Storage_FileSystem",
 ]
 

openvmm/openvmm_entry/src/lib.rs

@@ -1920,6 +1920,7 @@ async fn vm_config_from_command_line(
             fs: virtio_resources::fs::VirtioFsBackend::HostFs {
                 root_path: args.path.clone(),
                 mount_options: args.options.clone(),
+                windows_options: None,
             },
         }
         .into_resource();