[VFS] Add NullDevice (returns success for all calls), handle \Device\Harddisk0\ with it

XMountUtilityDrive code tries reading/writing from \Device\Harddisk0\Cache0 / Cache1 / Partition0, NullDevice handling \Device\Harddisk0 will make that code think that the reads/writes were successful, so the utility-drive mount can proceed without failing.

src/xenia/vfs/devices/null_device.cc

@@ -0,0 +1,62 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2021 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#include "xenia/vfs/devices/null_device.h"
+
+#include "xenia/base/filesystem.h"
+#include "xenia/base/logging.h"
+#include "xenia/base/math.h"
+#include "xenia/kernel/xfile.h"
+#include "xenia/vfs/devices/null_entry.h"
+
+namespace xe {
+namespace vfs {
+
+NullDevice::NullDevice(const std::string& mount_path,
+                       const std::initializer_list<std::string>& null_paths)
+    : Device(mount_path), null_paths_(null_paths), name_("NullDevice") {}
+
+NullDevice::~NullDevice() = default;
+
+bool NullDevice::Initialize() {
+  auto root_entry = new NullEntry(this, nullptr, mount_path_);
+  root_entry->attributes_ = kFileAttributeDirectory;
+  root_entry_ = std::unique_ptr<Entry>(root_entry);
+
+  for (auto path : null_paths_) {
+    auto child = NullEntry::Create(this, root_entry, path);
+    root_entry->children_.push_back(std::unique_ptr<Entry>(child));
+  }
+  return true;
+}
+
+void NullDevice::Dump(StringBuffer* string_buffer) {
+  auto global_lock = global_critical_region_.Acquire();
+  root_entry_->Dump(string_buffer, 0);
+}
+
+Entry* NullDevice::ResolvePath(const std::string_view path) {
+  XELOGFS("NullDevice::ResolvePath({})", path);
+
+  auto root = root_entry_.get();
+  if (path.empty()) {
+    return root_entry_.get();
+  }
+
+  for (auto& child : root->children()) {
+    if (!strcasecmp(child->path().c_str(), path.data())) {
+      return child.get();
+    }
+  }
+
+  return nullptr;
+}
+
+}  // namespace vfs
+}  // namespace xe

src/xenia/vfs/devices/null_device.h

@@ -0,0 +1,57 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2021 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#ifndef XENIA_VFS_DEVICES_NULL_DEVICE_H_
+#define XENIA_VFS_DEVICES_NULL_DEVICE_H_
+
+#include <string>
+
+#include "xenia/vfs/device.h"
+
+namespace xe {
+namespace vfs {
+
+class NullEntry;
+
+class NullDevice : public Device {
+ public:
+  NullDevice(const std::string& mount_path,
+             const std::initializer_list<std::string>& null_paths);
+  ~NullDevice() override;
+
+  bool Initialize() override;
+  void Dump(StringBuffer* string_buffer) override;
+  Entry* ResolvePath(const std::string_view path) override;
+
+  bool is_read_only() const override { return false; }
+
+  const std::string& name() const override { return name_; }
+  uint32_t attributes() const override { return 0; }
+  uint32_t component_name_max_length() const override { return 40; }
+
+  uint32_t total_allocation_units() const override { return 0x10; }
+  uint32_t available_allocation_units() const override { return 0x10; }
+
+  // STFC/cache code seems to require the product of the next two to equal
+  // 0x10000
+  uint32_t sectors_per_allocation_unit() const override { return 0x80; }
+
+  // STFC requires <= 0x1000
+  uint32_t bytes_per_sector() const override { return 0x200; }
+
+ private:
+  std::string name_;
+  std::unique_ptr<Entry> root_entry_;
+  std::vector<std::string> null_paths_;
+};
+
+}  // namespace vfs
+}  // namespace xe
+
+#endif  // XENIA_VFS_DEVICES_NULL_DEVICE_H_

src/xenia/vfs/devices/null_entry.cc

@@ -0,0 +1,55 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2021 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#include "xenia/vfs/devices/null_entry.h"
+
+#include "xenia/base/filesystem.h"
+#include "xenia/base/logging.h"
+#include "xenia/base/mapped_memory.h"
+#include "xenia/base/math.h"
+#include "xenia/base/string.h"
+#include "xenia/vfs/device.h"
+#include "xenia/vfs/devices/null_file.h"
+
+namespace xe {
+namespace vfs {
+
+NullEntry::NullEntry(Device* device, Entry* parent, std::string path)
+    : Entry(device, parent, path) {}
+
+NullEntry::~NullEntry() = default;
+
+NullEntry* NullEntry::Create(Device* device, Entry* parent,
+                             const std::string& path) {
+  auto entry = new NullEntry(device, parent, path);
+
+  entry->create_timestamp_ = 0;
+  entry->access_timestamp_ = 0;
+  entry->write_timestamp_ = 0;
+
+  entry->attributes_ = kFileAttributeNormal;
+
+  entry->size_ = 0;
+  entry->allocation_size_ = 0;
+  return entry;
+}
+
+X_STATUS NullEntry::Open(uint32_t desired_access, File** out_file) {
+  if (is_read_only() && (desired_access & (FileAccess::kFileWriteData |
+                                           FileAccess::kFileAppendData))) {
+    XELOGE("Attempting to open file for write access on read-only device");
+    return X_STATUS_ACCESS_DENIED;
+  }
+
+  *out_file = new NullFile(desired_access, this);
+  return X_STATUS_SUCCESS;
+}
+
+}  // namespace vfs
+}  // namespace xe

src/xenia/vfs/devices/null_entry.h

@@ -0,0 +1,42 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2021 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#ifndef XENIA_VFS_DEVICES_NULL_ENTRY_H_
+#define XENIA_VFS_DEVICES_NULL_ENTRY_H_
+
+#include <string>
+
+#include "xenia/base/filesystem.h"
+#include "xenia/vfs/entry.h"
+
+namespace xe {
+namespace vfs {
+
+class NullDevice;
+
+class NullEntry : public Entry {
+ public:
+  NullEntry(Device* device, Entry* parent, std::string path);
+  ~NullEntry() override;
+
+  static NullEntry* Create(Device* device, Entry* parent,
+                           const std::string& path);
+
+  X_STATUS Open(uint32_t desired_access, File** out_file) override;
+
+  bool can_map() const override { return false; }
+
+ private:
+  friend class NullDevice;
+};
+
+}  // namespace vfs
+}  // namespace xe
+
+#endif  // XENIA_VFS_DEVICES_NULL_ENTRY_H_

src/xenia/vfs/devices/null_file.cc

@@ -0,0 +1,52 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2021 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#include "xenia/vfs/devices/null_file.h"
+
+#include "xenia/vfs/devices/null_entry.h"
+
+namespace xe {
+namespace vfs {
+
+NullFile::NullFile(uint32_t file_access, NullEntry* entry)
+    : File(file_access, entry) {}
+
+NullFile::~NullFile() = default;
+
+void NullFile::Destroy() { delete this; }
+
+X_STATUS NullFile::ReadSync(void* buffer, size_t buffer_length,
+                            size_t byte_offset, size_t* out_bytes_read) {
+  if (!(file_access_ & FileAccess::kFileReadData)) {
+    return X_STATUS_ACCESS_DENIED;
+  }
+
+  return X_STATUS_SUCCESS;
+}
+
+X_STATUS NullFile::WriteSync(const void* buffer, size_t buffer_length,
+                             size_t byte_offset, size_t* out_bytes_written) {
+  if (!(file_access_ &
+        (FileAccess::kFileWriteData | FileAccess::kFileAppendData))) {
+    return X_STATUS_ACCESS_DENIED;
+  }
+
+  return X_STATUS_SUCCESS;
+}
+
+X_STATUS NullFile::SetLength(size_t length) {
+  if (!(file_access_ & FileAccess::kFileWriteData)) {
+    return X_STATUS_ACCESS_DENIED;
+  }
+
+  return X_STATUS_SUCCESS;
+}
+
+}  // namespace vfs
+}  // namespace xe

src/xenia/vfs/devices/null_file.h

@@ -0,0 +1,40 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2021 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#ifndef XENIA_VFS_DEVICES_NULL_FILE_H_
+#define XENIA_VFS_DEVICES_NULL_FILE_H_
+
+#include <string>
+
+#include "xenia/base/filesystem.h"
+#include "xenia/vfs/file.h"
+
+namespace xe {
+namespace vfs {
+
+class NullEntry;
+
+class NullFile : public File {
+ public:
+  NullFile(uint32_t file_access, NullEntry* entry);
+  ~NullFile() override;
+
+  void Destroy() override;
+
+  X_STATUS ReadSync(void* buffer, size_t buffer_length, size_t byte_offset,
+                    size_t* out_bytes_read) override;
+  X_STATUS WriteSync(const void* buffer, size_t buffer_length,
+                     size_t byte_offset, size_t* out_bytes_written) override;
+  X_STATUS SetLength(size_t length) override;
+};
+
+}  // namespace vfs
+}  // namespace xe
+
+#endif  // XENIA_VFS_DEVICES_NULL_FILE_H_