Revert "dawn_wire: Implement CreateBufferMapped on top of mappedAtCreation"

This reverts commit 0811ecc775.

Reason for revert: Makes the Dawn roll fail.

Original change's description:
> dawn_wire: Implement CreateBufferMapped on top of mappedAtCreation
> 
> This inverts the shimming to have the old mapping at creation method
> be implemented on top of the new method..
> 
> Also updates Wire tests to use mappedAtCreation instead of
> CreateBufferMapped.
> 
> Bug: dawn:445
> 
> Change-Id: I77dcfe72040e5bf187c41fe99c8dd785d5156a07
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/25701
> Commit-Queue: Corentin Wallez <cwallez@chromium.org>
> Reviewed-by: Austin Eng <enga@chromium.org>

TBR=cwallez@chromium.org,senorblanco@chromium.org,enga@chromium.org

Change-Id: Ied940d505fdf576860697dee8df2548c73581eba
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: dawn:445
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/25980
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

dawn_wire.json

@@ -38,7 +38,7 @@
             { "name": "write flush info length", "type": "uint64_t" },
             { "name": "write flush info", "type": "uint8_t", "annotation": "const*", "length": "write flush info length", "skip_serialize": true}
         ],
-        "device create buffer": [
+        "device create buffer mapped": [
             { "name": "device", "type": "device" },
             { "name": "descriptor", "type": "buffer descriptor", "annotation": "const*" },
             { "name": "result", "type": "ObjectHandle", "handle_type": "buffer" },
@@ -108,8 +108,6 @@
             "BufferSetSubData",
             "BufferGetConstMappedRange",
             "BufferGetMappedRange",
-            "DeviceCreateBuffer",
-            "DeviceCreateBufferMapped",
             "DevicePopErrorScope",
             "DeviceSetDeviceLostCallback",
             "DeviceSetUncapturedErrorCallback",
@@ -121,6 +119,8 @@
         "client_handwritten_commands": [
             "BufferDestroy",
             "BufferUnmap",
+            "DeviceCreateBuffer",
+            "DeviceCreateBufferMapped",
             "DeviceCreateErrorBuffer",
             "DeviceGetDefaultQueue",
             "DeviceInjectError",

src/dawn_wire/client/Buffer.cpp

@@ -29,61 +29,89 @@ namespace dawn_wire { namespace client {
             return device_->CreateErrorBuffer();
         }
 
-        std::unique_ptr<MemoryTransferService::WriteHandle> writeHandle = nullptr;
-        void* writeData = nullptr;
-        size_t writeHandleCreateInfoLength = 0;
-
-        // If the buffer is mapped at creation, create a write handle that will represent the
-        // mapping of the whole buffer.
-        if (descriptor->mappedAtCreation) {
-            // Create the handle.
-            writeHandle.reset(
-                wireClient->GetMemoryTransferService()->CreateWriteHandle(descriptor->size));
-            if (writeHandle == nullptr) {
-                device_->InjectError(WGPUErrorType_OutOfMemory, "Buffer mapping allocation failed");
-                return device_->CreateErrorBuffer();
-            }
-
-            // Open the handle, it may fail by returning a nullptr in writeData.
-            size_t writeDataLength = 0;
-            std::tie(writeData, writeDataLength) = writeHandle->Open();
-            if (writeData == nullptr) {
-                device_->InjectError(WGPUErrorType_OutOfMemory, "Buffer mapping allocation failed");
-                return device_->CreateErrorBuffer();
-            }
-            ASSERT(writeDataLength == descriptor->size);
-
-            // Get the serialization size of the write handle.
-            writeHandleCreateInfoLength = writeHandle->SerializeCreateSize();
-        }
-
-        // Create the buffer and send the creation command.
         auto* bufferObjectAndSerial = wireClient->BufferAllocator().New(device_);
         Buffer* buffer = bufferObjectAndSerial->object.get();
+        // Store the size of the buffer so that mapping operations can allocate a
+        // MemoryTransfer handle of the proper size.
         buffer->mSize = descriptor->size;
 
         DeviceCreateBufferCmd cmd;
+        cmd.self = ToAPI(device_);
+        cmd.descriptor = descriptor;
+        cmd.result = ObjectHandle{buffer->id, bufferObjectAndSerial->generation};
+
+        wireClient->SerializeCommand(cmd);
+
+        return ToAPI(buffer);
+    }
+
+    // static
+    WGPUCreateBufferMappedResult Buffer::CreateMapped(Device* device_,
+                                                      const WGPUBufferDescriptor* descriptor) {
+        Client* wireClient = device_->GetClient();
+
+        WGPUCreateBufferMappedResult result;
+        result.data = nullptr;
+        result.dataLength = 0;
+
+        // This buffer is too large to be mapped and to make a WriteHandle for.
+        if (descriptor->size > std::numeric_limits<size_t>::max()) {
+            device_->InjectError(WGPUErrorType_OutOfMemory, "Buffer is too large for mapping");
+            result.buffer = device_->CreateErrorBuffer();
+            return result;
+        }
+
+        // Create a WriteHandle for the map request. This is the client's intent to write GPU
+        // memory.
+        std::unique_ptr<MemoryTransferService::WriteHandle> writeHandle =
+            std::unique_ptr<MemoryTransferService::WriteHandle>(
+                wireClient->GetMemoryTransferService()->CreateWriteHandle(descriptor->size));
+
+        if (writeHandle == nullptr) {
+            device_->InjectError(WGPUErrorType_OutOfMemory, "Buffer mapping allocation failed");
+            result.buffer = device_->CreateErrorBuffer();
+            return result;
+        }
+
+        // CreateBufferMapped is synchronous and the staging buffer for upload should be immediately
+        // available.
+        // Open the WriteHandle. This returns a pointer and size of mapped memory.
+        // |result.data| may be null on error.
+        std::tie(result.data, result.dataLength) = writeHandle->Open();
+        if (result.data == nullptr) {
+            device_->InjectError(WGPUErrorType_OutOfMemory, "Buffer mapping allocation failed");
+            result.buffer = device_->CreateErrorBuffer();
+            return result;
+        }
+
+        auto* bufferObjectAndSerial = wireClient->BufferAllocator().New(device_);
+        Buffer* buffer = bufferObjectAndSerial->object.get();
+        buffer->mSize = descriptor->size;
+        // Successfully created staging memory. The buffer now owns the WriteHandle.
+        buffer->mWriteHandle = std::move(writeHandle);
+        buffer->mMappedData = result.data;
+        buffer->mMapOffset = 0;
+        buffer->mMapSize = descriptor->size;
+
+        result.buffer = ToAPI(buffer);
+
+        // Get the serialization size of the WriteHandle.
+        size_t handleCreateInfoLength = buffer->mWriteHandle->SerializeCreateSize();
+
+        DeviceCreateBufferMappedCmd cmd;
         cmd.device = ToAPI(device_);
         cmd.descriptor = descriptor;
         cmd.result = ObjectHandle{buffer->id, bufferObjectAndSerial->generation};
-        cmd.handleCreateInfoLength = writeHandleCreateInfoLength;
+        cmd.handleCreateInfoLength = handleCreateInfoLength;
         cmd.handleCreateInfo = nullptr;
 
-        char* writeHandleSpace = wireClient->SerializeCommand(cmd, writeHandleCreateInfoLength);
+        char* writeHandleSpace =
+            buffer->device->GetClient()->SerializeCommand(cmd, handleCreateInfoLength);
 
-        if (descriptor->mappedAtCreation) {
         // Serialize the WriteHandle into the space after the command.
-            writeHandle->SerializeCreate(writeHandleSpace);
+        buffer->mWriteHandle->SerializeCreate(writeHandleSpace);
 
-            // Set the buffer state for the mapping at creation. The buffer now owns the write
+        return result;
-            // handle..
-            buffer->mWriteHandle = std::move(writeHandle);
-            buffer->mMappedData = writeData;
-            buffer->mMapOffset = 0;
-            buffer->mMapSize = buffer->mSize;
-        }
-
-        return ToAPI(buffer);
     }
 
     // static

src/dawn_wire/client/Buffer.h

@@ -29,6 +29,8 @@ namespace dawn_wire { namespace client {
         using ObjectBase::ObjectBase;
 
         static WGPUBuffer Create(Device* device, const WGPUBufferDescriptor* descriptor);
+        static WGPUCreateBufferMappedResult CreateMapped(Device* device,
+                                                         const WGPUBufferDescriptor* descriptor);
         static WGPUBuffer CreateError(Device* device);
 
         ~Buffer();

src/dawn_wire/client/Device.cpp

@@ -146,20 +146,16 @@ namespace dawn_wire { namespace client {
     }
 
     WGPUBuffer Device::CreateBuffer(const WGPUBufferDescriptor* descriptor) {
+        if (descriptor->mappedAtCreation) {
+            return CreateBufferMapped(descriptor).buffer;
+        } else {
             return Buffer::Create(this, descriptor);
         }
+    }
 
     WGPUCreateBufferMappedResult Device::CreateBufferMapped(
         const WGPUBufferDescriptor* descriptor) {
-        WGPUBufferDescriptor descMappedAtCreation = *descriptor;
+        return Buffer::CreateMapped(this, descriptor);
-        descMappedAtCreation.mappedAtCreation = true;
-
-        WGPUCreateBufferMappedResult result;
-        result.buffer = CreateBuffer(&descMappedAtCreation);
-        result.data = FromAPI(result.buffer)->GetMappedRange(0, descriptor->size);
-        result.dataLength = result.data == nullptr ? 0 : descriptor->size;
-
-        return result;
     }
 
     WGPUBuffer Device::CreateErrorBuffer() {

src/dawn_wire/server/ServerBuffer.cpp

@@ -118,52 +118,50 @@ namespace dawn_wire { namespace server {
         return true;
     }
 
-    bool Server::DoDeviceCreateBuffer(WGPUDevice device,
+    bool Server::DoDeviceCreateBufferMapped(WGPUDevice device,
                                             const WGPUBufferDescriptor* descriptor,
                                             ObjectHandle bufferResult,
                                             uint64_t handleCreateInfoLength,
                                             const uint8_t* handleCreateInfo) {
-        // Create and register the buffer object.
+        if (handleCreateInfoLength > std::numeric_limits<size_t>::max()) {
+            // This is the size of data deserialized from the command stream, which must be
+            // CPU-addressable.
+            return false;
+        }
+
         auto* resultData = BufferObjects().Allocate(bufferResult.id);
         if (resultData == nullptr) {
             return false;
         }
         resultData->generation = bufferResult.generation;
-        resultData->handle = mProcs.deviceCreateBuffer(device, descriptor);
 
-        // If the buffer isn't mapped at creation, we are done.
+        WGPUCreateBufferMappedResult result = mProcs.deviceCreateBufferMapped(device, descriptor);
-        if (!descriptor->mappedAtCreation) {
+        ASSERT(result.buffer != nullptr);
-            return handleCreateInfoLength == 0;
+        if (result.data == nullptr && result.dataLength != 0) {
-        }
+            // Non-zero dataLength but null data is used to indicate an allocation error.
-
+            // Don't return false because this is not fatal. result.buffer is an ErrorBuffer
-        // This is the size of data deserialized from the command stream to create the write handle,
+            // and subsequent operations will be errors.
-        // which must be CPU-addressable.
+            // This should only happen when fuzzing with the Null backend.
-        if (handleCreateInfoLength > std::numeric_limits<size_t>::max()) {
-            return false;
-        }
-
-        void* mapping = mProcs.bufferGetMappedRange(resultData->handle, 0, descriptor->size);
-        if (mapping == nullptr) {
-            // A zero mapping is used to indicate an allocation error of an error buffer. This is a
-            // valid case and isn't fatal. Remember the buffer is an error so as to skip subsequent
-            // mapping operations.
             resultData->mapWriteState = BufferMapWriteState::MapError;
-            return true;
+        } else {
-        }
-
             // Deserialize metadata produced from the client to create a companion server handle.
             MemoryTransferService::WriteHandle* writeHandle = nullptr;
             if (!mMemoryTransferService->DeserializeWriteHandle(
                     handleCreateInfo, static_cast<size_t>(handleCreateInfoLength), &writeHandle)) {
                 return false;
             }
+            ASSERT(writeHandle != nullptr);
 
             // Set the target of the WriteHandle to the mapped GPU memory.
-        ASSERT(writeHandle != nullptr);
+            writeHandle->SetTarget(result.data, result.dataLength);
-        writeHandle->SetTarget(mapping, descriptor->size);
 
+            // The buffer is mapped and has a valid mappedData pointer.
+            // The buffer may still be an error with fake staging data.
             resultData->mapWriteState = BufferMapWriteState::Mapped;
-        resultData->writeHandle.reset(writeHandle);
+            resultData->writeHandle =
+                std::unique_ptr<MemoryTransferService::WriteHandle>(writeHandle);
+        }
+        resultData->handle = result.buffer;
 
         return true;
     }

src/tests/unittests/wire/WireBufferMappingTests.cpp

@@ -477,72 +477,84 @@ TEST_F(WireBufferMappingTests, DestroyInsideMapWriteCallback) {
     FlushClient();
 }
 
-// Test successful buffer creation with mappedAtCreation=true
+// Test successful CreateBufferMapped
-TEST_F(WireBufferMappingTests, MappedAtCreationSuccess) {
+TEST_F(WireBufferMappingTests, CreateBufferMappedSuccess) {
     WGPUBufferDescriptor descriptor = {};
     descriptor.size = 4;
-    descriptor.mappedAtCreation = true;
 
     WGPUBuffer apiBuffer = api.GetNewBuffer();
+    WGPUCreateBufferMappedResult apiResult;
     uint32_t apiBufferData = 1234;
+    apiResult.buffer = apiBuffer;
+    apiResult.data = reinterpret_cast<uint8_t*>(&apiBufferData);
+    apiResult.dataLength = 4;
 
-    WGPUBuffer buffer = wgpuDeviceCreateBuffer(device, &descriptor);
+    WGPUCreateBufferMappedResult result = wgpuDeviceCreateBufferMapped(device, &descriptor);
 
-    EXPECT_CALL(api, DeviceCreateBuffer(apiDevice, _)).WillOnce(Return(apiBuffer));
+    EXPECT_CALL(api, DeviceCreateBufferMapped(apiDevice, _))
-    EXPECT_CALL(api, BufferGetMappedRange(apiBuffer, 0, 4)).WillOnce(Return(&apiBufferData));
+        .WillOnce(Return(apiResult))
+        .RetiresOnSaturation();
 
     FlushClient();
 
-    wgpuBufferUnmap(buffer);
+    wgpuBufferUnmap(result.buffer);
     EXPECT_CALL(api, BufferUnmap(apiBuffer)).Times(1);
 
     FlushClient();
 }
 
-// Test that releasing a buffer mapped at creation does not call Unmap
+// Test that releasing after CreateBufferMapped does not call Unmap
-TEST_F(WireBufferMappingTests, MappedAtCreationReleaseBeforeUnmap) {
+TEST_F(WireBufferMappingTests, ReleaseAfterCreateBufferMapped) {
     WGPUBufferDescriptor descriptor = {};
     descriptor.size = 4;
-    descriptor.mappedAtCreation = true;
 
     WGPUBuffer apiBuffer = api.GetNewBuffer();
+    WGPUCreateBufferMappedResult apiResult;
     uint32_t apiBufferData = 1234;
+    apiResult.buffer = apiBuffer;
+    apiResult.data = reinterpret_cast<uint8_t*>(&apiBufferData);
+    apiResult.dataLength = 4;
 
-    WGPUBuffer buffer = wgpuDeviceCreateBuffer(device, &descriptor);
+    WGPUCreateBufferMappedResult result = wgpuDeviceCreateBufferMapped(device, &descriptor);
 
-    EXPECT_CALL(api, DeviceCreateBuffer(apiDevice, _)).WillOnce(Return(apiBuffer));
+    EXPECT_CALL(api, DeviceCreateBufferMapped(apiDevice, _))
-    EXPECT_CALL(api, BufferGetMappedRange(apiBuffer, 0, 4)).WillOnce(Return(&apiBufferData));
+        .WillOnce(Return(apiResult))
+        .RetiresOnSaturation();
 
     FlushClient();
 
-    wgpuBufferRelease(buffer);
+    wgpuBufferRelease(result.buffer);
     EXPECT_CALL(api, BufferRelease(apiBuffer)).Times(1);
 
     FlushClient();
 }
 
-// Test that it is valid to map a buffer after it is mapped at creation and unmapped
+// Test that it is valid to map a buffer after CreateBufferMapped and Unmap
-TEST_F(WireBufferMappingTests, MappedAtCreationThenMapSuccess) {
+TEST_F(WireBufferMappingTests, CreateBufferMappedThenMapSuccess) {
     WGPUBufferDescriptor descriptor = {};
     descriptor.size = 4;
-    descriptor.mappedAtCreation = true;
 
     WGPUBuffer apiBuffer = api.GetNewBuffer();
-    uint32_t apiBufferData = 1234;
+    WGPUCreateBufferMappedResult apiResult;
+    uint32_t apiBufferData = 9863;
+    apiResult.buffer = apiBuffer;
+    apiResult.data = reinterpret_cast<uint8_t*>(&apiBufferData);
+    apiResult.dataLength = 4;
 
-    WGPUBuffer buffer = wgpuDeviceCreateBuffer(device, &descriptor);
+    WGPUCreateBufferMappedResult result = wgpuDeviceCreateBufferMapped(device, &descriptor);
 
-    EXPECT_CALL(api, DeviceCreateBuffer(apiDevice, _)).WillOnce(Return(apiBuffer));
+    EXPECT_CALL(api, DeviceCreateBufferMapped(apiDevice, _))
-    EXPECT_CALL(api, BufferGetMappedRange(apiBuffer, 0, 4)).WillOnce(Return(&apiBufferData));
+        .WillOnce(Return(apiResult))
+        .RetiresOnSaturation();
 
     FlushClient();
 
-    wgpuBufferUnmap(buffer);
+    wgpuBufferUnmap(result.buffer);
     EXPECT_CALL(api, BufferUnmap(apiBuffer)).Times(1);
 
     FlushClient();
 
-    wgpuBufferMapWriteAsync(buffer, ToMockBufferMapWriteCallback, nullptr);
+    wgpuBufferMapWriteAsync(result.buffer, ToMockBufferMapWriteCallback, nullptr);
 
     uint32_t zero = 0;
     EXPECT_CALL(api, OnBufferMapAsyncCallback(apiBuffer, _, _)).WillOnce(InvokeWithoutArgs([&]() {
@@ -560,23 +572,27 @@ TEST_F(WireBufferMappingTests, MappedAtCreationThenMapSuccess) {
     FlushServer();
 }
 
-// Test that it is invalid to map a buffer after mappedAtCreation but before Unmap
+// Test that it is invalid to map a buffer after CreateBufferMapped before Unmap
-TEST_F(WireBufferMappingTests, MappedAtCreationThenMapFailure) {
+TEST_F(WireBufferMappingTests, CreateBufferMappedThenMapFailure) {
     WGPUBufferDescriptor descriptor = {};
     descriptor.size = 4;
-    descriptor.mappedAtCreation = true;
 
     WGPUBuffer apiBuffer = api.GetNewBuffer();
-    uint32_t apiBufferData = 1234;
+    WGPUCreateBufferMappedResult apiResult;
+    uint32_t apiBufferData = 9863;
+    apiResult.buffer = apiBuffer;
+    apiResult.data = reinterpret_cast<uint8_t*>(&apiBufferData);
+    apiResult.dataLength = 4;
 
-    WGPUBuffer buffer = wgpuDeviceCreateBuffer(device, &descriptor);
+    WGPUCreateBufferMappedResult result = wgpuDeviceCreateBufferMapped(device, &descriptor);
 
-    EXPECT_CALL(api, DeviceCreateBuffer(apiDevice, _)).WillOnce(Return(apiBuffer));
+    EXPECT_CALL(api, DeviceCreateBufferMapped(apiDevice, _))
-    EXPECT_CALL(api, BufferGetMappedRange(apiBuffer, 0, 4)).WillOnce(Return(&apiBufferData));
+        .WillOnce(Return(apiResult))
+        .RetiresOnSaturation();
 
     FlushClient();
 
-    wgpuBufferMapWriteAsync(buffer, ToMockBufferMapWriteCallback, nullptr);
+    wgpuBufferMapWriteAsync(result.buffer, ToMockBufferMapWriteCallback, nullptr);
 
     EXPECT_CALL(api, OnBufferMapAsyncCallback(apiBuffer, _, _)).WillOnce(InvokeWithoutArgs([&]() {
         api.CallMapAsyncCallback(apiBuffer, WGPUBufferMapAsyncStatus_Error);
@@ -589,7 +605,7 @@ TEST_F(WireBufferMappingTests, MappedAtCreationThenMapFailure) {
 
     FlushServer();
 
-    wgpuBufferUnmap(buffer);
+    wgpuBufferUnmap(result.buffer);
     EXPECT_CALL(api, BufferUnmap(apiBuffer)).Times(1);
 
     FlushClient();

src/tests/unittests/wire/WireMemoryTransferServiceTests.cpp

@@ -155,20 +155,24 @@ class WireMemoryTransferServiceTests : public WireTest {
         return std::make_pair(apiBuffer, buffer);
     }
 
-    std::pair<WGPUBuffer, WGPUBuffer> CreateBufferMapped() {
+    std::pair<WGPUCreateBufferMappedResult, WGPUCreateBufferMappedResult> CreateBufferMapped() {
         WGPUBufferDescriptor descriptor = {};
         descriptor.size = sizeof(mBufferContent);
-        descriptor.mappedAtCreation = true;
 
         WGPUBuffer apiBuffer = api.GetNewBuffer();
 
-        WGPUBuffer buffer = wgpuDeviceCreateBuffer(device, &descriptor);
+        WGPUCreateBufferMappedResult apiResult;
+        apiResult.buffer = apiBuffer;
+        apiResult.data = reinterpret_cast<uint8_t*>(&mMappedBufferContent);
+        apiResult.dataLength = sizeof(mMappedBufferContent);
 
-        EXPECT_CALL(api, DeviceCreateBuffer(apiDevice, _)).WillOnce(Return(apiBuffer));
+        WGPUCreateBufferMappedResult result = wgpuDeviceCreateBufferMapped(device, &descriptor);
-        EXPECT_CALL(api, BufferGetMappedRange(apiBuffer, 0, sizeof(mBufferContent)))
-            .WillOnce(Return(&mMappedBufferContent));
 
-        return std::make_pair(apiBuffer, buffer);
+        EXPECT_CALL(api, DeviceCreateBufferMapped(apiDevice, _))
+            .WillOnce(Return(apiResult))
+            .RetiresOnSaturation();
+
+        return std::make_pair(apiResult, result);
     }
 
     ClientReadHandle* ExpectReadHandleCreation() {
@@ -887,8 +891,8 @@ TEST_F(WireMemoryTransferServiceTests, BufferMapWriteDestroyBeforeUnmap) {
     }
 }
 
-// Test successful buffer creation with mappedAtCreation = true.
+// Test successful CreateBufferMapped.
-TEST_F(WireMemoryTransferServiceTests, MappedAtCreationSuccess) {
+TEST_F(WireMemoryTransferServiceTests, CreateBufferMappedSuccess) {
     // The client should create and serialize a WriteHandle on createBufferMapped.
     ClientWriteHandle* clientHandle = ExpectWriteHandleCreation();
 
@@ -900,9 +904,9 @@ TEST_F(WireMemoryTransferServiceTests, MappedAtCreationSuccess) {
     // The server should then deserialize the WriteHandle from the client.
     ServerWriteHandle* serverHandle = ExpectServerWriteHandleDeserialization();
 
-    WGPUBuffer buffer;
+    WGPUCreateBufferMappedResult result;
-    WGPUBuffer apiBuffer;
+    WGPUCreateBufferMappedResult apiResult;
-    std::tie(apiBuffer, buffer) = CreateBufferMapped();
+    std::tie(apiResult, result) = CreateBufferMapped();
     FlushClient();
 
     // Update the mapped contents.
@@ -912,33 +916,35 @@ TEST_F(WireMemoryTransferServiceTests, MappedAtCreationSuccess) {
     ExpectClientWriteHandleSerializeFlush(clientHandle);
     EXPECT_CALL(clientMemoryTransferService, OnWriteHandleDestroy(clientHandle)).Times(1);
 
-    wgpuBufferUnmap(buffer);
+    wgpuBufferUnmap(result.buffer);
 
     // The server deserializes the Flush message.
     ExpectServerWriteHandleDeserializeFlush(serverHandle, mUpdatedBufferContent);
 
     // After the handle is updated it can be destroyed.
     EXPECT_CALL(serverMemoryTransferService, OnWriteHandleDestroy(serverHandle)).Times(1);
-    EXPECT_CALL(api, BufferUnmap(apiBuffer)).Times(1);
+    EXPECT_CALL(api, BufferUnmap(apiResult.buffer)).Times(1);
 
     FlushClient();
 }
 
-// Test buffer creation with mappedAtCreation WriteHandle creation failure.
+// Test CreateBufferMapped WriteHandle creation failure.
-TEST_F(WireMemoryTransferServiceTests, MappedAtCreationWriteHandleCreationFailure) {
+TEST_F(WireMemoryTransferServiceTests, CreateBufferMappedWriteHandleCreationFailure) {
     // Mock a WriteHandle creation failure
     MockWriteHandleCreationFailure();
 
     WGPUBufferDescriptor descriptor = {};
     descriptor.size = sizeof(mBufferContent);
-    descriptor.mappedAtCreation = true;
 
-    WGPUBuffer buffer = wgpuDeviceCreateBuffer(device, &descriptor);
+    WGPUCreateBufferMappedResult result = wgpuDeviceCreateBufferMapped(device, &descriptor);
-    EXPECT_EQ(nullptr, wgpuBufferGetMappedRange(buffer, 0, sizeof(mBufferContent)));
+
+    // TODO(enga): Check that the client generated a context lost.
+    EXPECT_EQ(result.data, nullptr);
+    EXPECT_EQ(result.dataLength, 0u);
 }
 
-// Test buffer creation with mappedAtCreation DeserializeWriteHandle failure.
+// Test CreateBufferMapped DeserializeWriteHandle failure.
-TEST_F(WireMemoryTransferServiceTests, MappedAtCreationDeserializeWriteHandleFailure) {
+TEST_F(WireMemoryTransferServiceTests, CreateBufferMappedDeserializeWriteHandleFailure) {
     // The client should create and serialize a WriteHandle on createBufferMapped.
     ClientWriteHandle* clientHandle = ExpectWriteHandleCreation();
 
@@ -950,16 +956,16 @@ TEST_F(WireMemoryTransferServiceTests, MappedAtCreationDeserializeWriteHandleFai
     // The server should then deserialize the WriteHandle from the client.
     MockServerWriteHandleDeserializeFailure();
 
-    WGPUBuffer buffer;
+    WGPUCreateBufferMappedResult result;
-    WGPUBuffer apiBuffer;
+    WGPUCreateBufferMappedResult apiResult;
-    std::tie(apiBuffer, buffer) = CreateBufferMapped();
+    std::tie(apiResult, result) = CreateBufferMapped();
     FlushClient(false);
 
     EXPECT_CALL(clientMemoryTransferService, OnWriteHandleDestroy(clientHandle)).Times(1);
 }
 
-// Test buffer creation with mappedAtCreation handle Open failure.
+// Test CreateBufferMapped handle Open failure.
-TEST_F(WireMemoryTransferServiceTests, MappedAtCreationHandleOpenFailure) {
+TEST_F(WireMemoryTransferServiceTests, CreateBufferMappedHandleOpenFailure) {
     // The client should create a WriteHandle on createBufferMapped.
     ClientWriteHandle* clientHandle = ExpectWriteHandleCreation();
 
@@ -973,14 +979,16 @@ TEST_F(WireMemoryTransferServiceTests, MappedAtCreationHandleOpenFailure) {
 
     WGPUBufferDescriptor descriptor = {};
     descriptor.size = sizeof(mBufferContent);
-    descriptor.mappedAtCreation = true;
 
-    WGPUBuffer buffer = wgpuDeviceCreateBuffer(device, &descriptor);
+    WGPUCreateBufferMappedResult result = wgpuDeviceCreateBufferMapped(device, &descriptor);
-    EXPECT_EQ(nullptr, wgpuBufferGetMappedRange(buffer, 0, sizeof(mBufferContent)));
+
+    // TODO(enga): Check that the client generated a context lost.
+    EXPECT_EQ(result.data, nullptr);
+    EXPECT_EQ(result.dataLength, 0u);
 }
 
-// Test buffer creation with mappedAtCreation = true DeserializeFlush failure.
+// Test CreateBufferMapped DeserializeFlush failure.
-TEST_F(WireMemoryTransferServiceTests, MappedAtCreationDeserializeFlushFailure) {
+TEST_F(WireMemoryTransferServiceTests, CreateBufferMappedDeserializeFlushFailure) {
     // The client should create and serialize a WriteHandle on createBufferMapped.
     ClientWriteHandle* clientHandle = ExpectWriteHandleCreation();
 
@@ -992,9 +1000,9 @@ TEST_F(WireMemoryTransferServiceTests, MappedAtCreationDeserializeFlushFailure)
     // The server should then deserialize the WriteHandle from the client.
     ServerWriteHandle* serverHandle = ExpectServerWriteHandleDeserialization();
 
-    WGPUBuffer buffer;
+    WGPUCreateBufferMappedResult result;
-    WGPUBuffer apiBuffer;
+    WGPUCreateBufferMappedResult apiResult;
-    std::tie(apiBuffer, buffer) = CreateBufferMapped();
+    std::tie(apiResult, result) = CreateBufferMapped();
     FlushClient();
 
     // Update the mapped contents.
@@ -1004,7 +1012,7 @@ TEST_F(WireMemoryTransferServiceTests, MappedAtCreationDeserializeFlushFailure)
     ExpectClientWriteHandleSerializeFlush(clientHandle);
     EXPECT_CALL(clientMemoryTransferService, OnWriteHandleDestroy(clientHandle)).Times(1);
 
-    wgpuBufferUnmap(buffer);
+    wgpuBufferUnmap(result.buffer);
 
     // The server deserializes the Flush message. Mock a deserialization failure.
     MockServerWriteHandleDeserializeFlushFailure(serverHandle);
@@ -1014,8 +1022,8 @@ TEST_F(WireMemoryTransferServiceTests, MappedAtCreationDeserializeFlushFailure)
     EXPECT_CALL(serverMemoryTransferService, OnWriteHandleDestroy(serverHandle)).Times(1);
 }
 
-// Test mappedAtCreation=true destroying the buffer before unmapping on the client side.
+// Test CreateBufferMapped destroying the buffer before unmapping on the client side.
-TEST_F(WireMemoryTransferServiceTests, MappedAtCreationDestroyBeforeUnmap) {
+TEST_F(WireMemoryTransferServiceTests, CreateBufferMappedDestroyBeforeUnmap) {
     // The client should create and serialize a WriteHandle on createBufferMapped.
     ClientWriteHandle* clientHandle = ExpectWriteHandleCreation();
 
@@ -1027,9 +1035,9 @@ TEST_F(WireMemoryTransferServiceTests, MappedAtCreationDestroyBeforeUnmap) {
     // The server should then deserialize the WriteHandle from the client.
     ServerWriteHandle* serverHandle = ExpectServerWriteHandleDeserialization();
 
-    WGPUBuffer buffer;
+    WGPUCreateBufferMappedResult result;
-    WGPUBuffer apiBuffer;
+    WGPUCreateBufferMappedResult apiResult;
-    std::tie(apiBuffer, buffer) = CreateBufferMapped();
+    std::tie(apiResult, result) = CreateBufferMapped();
     FlushClient();
 
     // Update the mapped contents.
@@ -1039,16 +1047,16 @@ TEST_F(WireMemoryTransferServiceTests, MappedAtCreationDestroyBeforeUnmap) {
     // immediately, both in the client and server side.
     {
         EXPECT_CALL(clientMemoryTransferService, OnWriteHandleDestroy(clientHandle)).Times(1);
-        wgpuBufferDestroy(buffer);
+        wgpuBufferDestroy(result.buffer);
 
         EXPECT_CALL(serverMemoryTransferService, OnWriteHandleDestroy(serverHandle)).Times(1);
-        EXPECT_CALL(api, BufferDestroy(apiBuffer)).Times(1);
+        EXPECT_CALL(api, BufferDestroy(apiResult.buffer)).Times(1);
         FlushClient();
 
         // The handle is already destroyed so unmap only results in a server unmap call.
-        wgpuBufferUnmap(buffer);
+        wgpuBufferUnmap(result.buffer);
 
-        EXPECT_CALL(api, BufferUnmap(apiBuffer)).Times(1);
+        EXPECT_CALL(api, BufferUnmap(apiResult.buffer)).Times(1);
         FlushClient();
     }
 }