TPM_ERROR and ScopedTssType: uses the first, creates the second.

scoped_tss_type.h

+// Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Implements a simple framework for scoping TSS values.
+// Based on chrome's base/scoped_ptr_malloc implementation.
+//
+// Example usage:
+//  ScopedTssContext context;

[gauravsh, 2011/03/29 19:16:06]

context_handle

[Will Drewry, 2011/03/29 19:42:22]

Ugh. I hate that variable name, but okay. :)

[gauravsh, 2011/03/29 20:21:54]

I just meant that you use context_handle later in this example, so be
consistent. :)

+//  TSS_RESULT result;
+//  if (!OpenAndConnectTpm(context_handle.get(), &result))

[gauravsh, 2011/03/29 20:21:54]

As I was saying, you use context_handle here, just make it consistent throughout
- either is fine.

+//    ...
+//  ScopedTssKey srk(*context);

[gauravsh, 2011/03/29 19:16:06]

context_handle

[Will Drewry, 2011/03/29 19:42:22]

Done.

+//  if (!LoadSrk(*context_handle, srk_handle.get(), &result))
+//    ...
+//
+// See the bottom of this file for common typedefs.
+
+#include <assert.h>
+#include <trousers/tss.h>
+#include <trousers/trousers.h>
+
+#include <base/compiler_specific.h>
+#include <vector>
+
+#ifndef CRYPTOHOME_SCOPED_TSS_TYPE_H_
+#define CRYPTOHOME_SCOPED_TSS_TYPE_H_
+
+namespace cryptohome {
+
+class ScopedTssContextRelease {
+ public:
+  inline void operator()(TSS_HCONTEXT unused, TSS_HCONTEXT context) const {
+    // Usually, only |context| is used, but if the ScopedTssContext is
+    // used slightly differently, it may end up with a context in |unused|.
+    // For now, treat that as a bug.
+    assert(unused == 0);
+    if (context)
+      Tspi_Context_Close(context);
+  }
+};
+
+class ScopedTssMemoryRelease {
+ public:
+  inline void operator()(TSS_HCONTEXT context, BYTE* memory) const {
+    if (memory)
+      Tspi_Context_FreeMemory(context, memory);

[gauravsh, 2011/03/29 19:16:06]

so in ScopedTssContextRelease, you check for (context) before calling close on
it. Any particularly reason why you don't this here.

Same comments for ScopeTssObjectRelease below (check for context and handle)

[Will Drewry, 2011/03/29 19:42:22]

For ContextRelease I assert it _is_ 0 and not that it isn't because  in that
case, we use the templated type for the context storage and not the context
itself.

However, I should be checking on the others ...

done!

+  }
+};
+
+class ScopedTssObjectRelease {
+ public:
+  inline void operator()(TSS_HCONTEXT context, TSS_HOBJECT handle) const {
+    Tspi_Context_CloseObject(context, handle);
+  }
+};
+
+// Provide a basic scoped container for TSS managed objects.
+template<class TssType, class ReleaseProc = ScopedTssObjectRelease>
+class ScopedTssType {
+ public:
+  explicit ScopedTssType(TSS_HCONTEXT c = 0, TssType t = 0) :
+     context_(c),
+     type_(t) {}
+  virtual ~ScopedTssType() {
+    release_(context_, type_);
+  }
+
+  // Allow pointer-like access for getting the value.
+  TssType& operator*() {
+    return type_;
+  }
+
+  // Return a pointer to the storage to allow in place changes.
+  // We could override &, but that seems like a bad idea.
+  virtual TssType* get() {
+    return &type_;
+  }
+
+  // Returns the assigned context.
+  virtual TSS_HCONTEXT context() {
+    return context_;
+  }
+
+  virtual TssType release() WARN_UNUSED_RESULT {
+    TssType tmp = type_;
+    type_ = 0;
+    context_ = 0;
+    return tmp;
+  }
+
+  virtual void reset(TSS_HCONTEXT c = 0, TssType t = 0) {
+    release_(context_, type_);
+    context_ = c;
+    type_ = t;
+  }
+
+ private:
+  static ReleaseProc const release_;
+  TSS_HCONTEXT context_;
+  TssType type_;
+};
+
+// Provide clear-cut helpers for the common cases.
+typedef ScopedTssType<TSS_HCONTEXT, ScopedTssContextRelease> ScopedTssContext;
+typedef ScopedTssType<BYTE*, ScopedTssMemoryRelease> ScopedTssMemory;
+
+typedef ScopedTssType<TSS_HOBJECT> ScopedTssObject;
+typedef ScopedTssType<TSS_HKEY> ScopedTssKey;
+typedef ScopedTssType<TSS_HPOLICY> ScopedTssPolicy;
+typedef ScopedTssType<TSS_HPCRS> ScopedTssPcrs;
+
+}  // namespace cryptohome
+
+#endif  // CRYPTOHOME_SCOPED_TSS_TYPE_H_