清楚詳解Android?進程間圖傳遞圖形buffer原理
進程間圖怎么傳遞圖形buffer
寫這篇文章的目的:講解 進程間圖怎么傳遞圖形buffer的
最近研究圖形緩存怎么在進程之間傳遞的,谷歌了所有的博客,發(fā)現(xiàn)沒人講的清楚
圖形緩存是Android繪制的核心內(nèi)容,8.0版本后卻沒有講清楚明白的。
source.android.com/docs/core/a… 這里handle中有些線索,但沒細說。
Android 不同進程間,并不傳遞圖形緩存,而是使用“共享內(nèi)存”機制操作圖形緩存。
但是“共享內(nèi)存”用到的fd怎么傳遞的,沒人講清楚
fd 時進程級別的 int 數(shù)值,正常情況不同進程的 fd 并不能傳遞。而 GraphicBuffer 這個對象怎么做到傳遞 共享內(nèi)存fd 的?Java層的 Parcel 類有個 writeFileDescriptor 函數(shù),用于傳遞 fd ,那么native層,hal層又是怎么傳遞的呢?
本文并不面面俱到,只講核心內(nèi)容。需要的一些比較硬的知識儲備:
- 了解binder
- 用戶層:binder數(shù)據(jù)傳輸中,數(shù)據(jù)對象Parcel類,生成序列化對象過程,以及解包過程。
- 內(nèi)核層:binder 內(nèi)核中,對不同數(shù)據(jù)對象的解析
- 內(nèi)存知識:了解共享內(nèi)存,了解mmap,了解內(nèi)存分配和映射的本質(zhì)
- 對內(nèi)存了解的不夠深的話,一些地方還是比較難去理解的,并不是單純看代碼看的懂的,這或許是大部分博客講不明白的原因
- 了解Linux驅(qū)動
- 了解Surface 到 SurfaceFlinger 交互過程
大綱
- 一、Surface::dequeueBuffer 代碼流程簡述
- 二、進程間圖傳遞圖形buffer詳解
- 【1】SurfaceFlinger進程 和 IAllocator 服務(wù)之間傳遞圖形顯示的Buffer
- 【2】App進程同 SurfaceFlinger 進程之間傳遞 GraphicBuffer 對象服務(wù)端 requestBuffer 流程
- 【3】linux內(nèi)核部分,binder驅(qū)動對 BINDER_TYPE_FDA 、BINDER_TYPE_FD 類型的處理
- 總結(jié):
一、Surface.dequeueBuffer 代碼流程簡述
圖形內(nèi)存的分配核心在于 Surface.dequeueBuffer
流程。
- Surface.dequeueBuffer會調(diào)用 BufferQueueProducer.dequeueBuffer 去 SurfaceFlinger 端獲取BufferSlot數(shù)組中可用Slot的下標值
- 這個 BufferSlot 如果沒有 GraphicBuffer,就會去new一個,并在構(gòu)造函數(shù)中申請圖形緩存,并把圖形緩存映射到當前進程
- 同時把 BufferQueueProducer::dequeueBuffer 返回值的標記位設(shè)置為
BUFFER_NEEDS_REALLOCATION
- BufferQueueProducer.dequeueBuffer 的返回值如果帶有
BUFFER_NEEDS_REALLOCATION
標記,會調(diào)用 BufferQueueProducer.requestBuffer 獲取 GraphicBuffer,同時把圖形緩存映射到當前進程
調(diào)用過程
- Surface.dequeueBuffer【App·進程端】
- BpGraphicBufferProducer.dequeueBuffer【接口層】
- BufferQueueProducer.dequeueBuffer 【SurfaceFlinger 進程端】
dequeueBuffer 函數(shù)參數(shù)outSlot指針帶回一個BufferSlot數(shù)組的下標 ,返回值返回標記位,但并未返回 GraphicBuffer
dequeueBuffer 函數(shù)中,在獲取的 BufferSlot 沒有GraphicBuffer時,會new一個GraphicBuffer,同時返回值的標記為 BUFFER_NEEDS_REALLOCATION
new GraphicBuffer( width, height, format, BQ_LAYER_COUNT, usage, {mConsumerName.string(), mConsumerName.size()});
- GraphicBuffer 構(gòu)造函數(shù)中會調(diào)用initWithSize,內(nèi)部調(diào)用分配圖形緩存的代碼
- initWithSize(inWidth, inHeight, inFormat, inLayerCount, inUsage, std::move(requestorName));
- GraphicBufferAllocator.allocate
- allocateHelper(width, height, format, layerCount, usage, handle, stride, requestorName, true)
- Gralloc4Allocator.allocate
- hwbinder 服務(wù)調(diào)用:
- IAllocator::getService()->allocate(descriptor, bufferCount,[&](const auto& tmpError, const auto& tmpStride,const auto& tmpBuffers){...}
- 之后的代碼需要看廠家的具體實現(xiàn),最后無非是調(diào)用到內(nèi)核驅(qū)動層分配內(nèi)存,比如調(diào)用ion驅(qū)動層分配ion內(nèi)存
- SurfaceFlinger 和 IAllocator 服務(wù)怎么傳遞 共享內(nèi)存的,轉(zhuǎn)“進程間圖傳遞圖形buffer詳解【1】”章節(jié)
- 回調(diào)函數(shù)中調(diào)用 IMapper.importBuffer(tmpBuffers[i], &outBufferHandles[i]); // 內(nèi)部使用 mmap 把內(nèi)存映射到當前進程
- Gralloc4Allocator.allocate
- allocateHelper(width, height, format, layerCount, usage, handle, stride, requestorName, true)
- GraphicBufferAllocator.allocate
- BufferQueueProducer.dequeueBuffer 【SurfaceFlinger 進程端】
- 在 dequeueBuffer 返回值的標記為 BUFFER_NEEDS_REALLOCATION 時,
- App端需要調(diào)用 requestBuffer,獲取 GraphicBuffer 對象,
- 同時,把 SurfaceFlinger 分配的圖形緩存,映射到App進程
- BpGraphicBufferProducer->requestBuffer(buf, &gbuf);【接口層】
- BufferQueueProducer.requestBuffer-----請求返回 GraphicBuffer 對象
- SurfaceFlinger 進程端 requestBuffer 代碼非常簡單,僅僅是把 dequeueBuffer 過程中分配的對象賦值給參數(shù) gbuf ,傳遞給 App
- 那么,圖形緩存的 fd 是怎么傳到App端的,App又是怎么映射的圖形緩存呢?
- 核心在 BpGraphicBufferProducer.requestBuffer 函數(shù)中 GraphicBuffer 對象的構(gòu)建過程:
- status_t result =remote()->transact(REQUEST_BUFFER, data, &reply);
- 接下來GraphicBuffer 傳輸過程,見 進程間圖傳遞圖形buffer詳解【2】
- *buf = new GraphicBuffer();
- result = reply.read(**buf);
- read 過程會調(diào)用 GraphicBuffer.unflatten
- GraphicBuffer.unflatten 函數(shù)內(nèi)部調(diào)用了 GraphicBufferMapper.importBuffer
- 內(nèi)部也是調(diào)用IMapper.importBuffer,最終使用 mmap 把內(nèi)存映射到當前進程
- 調(diào)用 mmap 過程,可以參考 hardware/google/gchips/GrallocHAL/src/hidl_common/Mapper.cpp 代碼
- cs.android.com/android/pla…
- GraphicBuffer.unflatten 函數(shù)內(nèi)部調(diào)用了 GraphicBufferMapper.importBuffer
- read 過程會調(diào)用 GraphicBuffer.unflatten
- status_t result =remote()->transact(REQUEST_BUFFER, data, &reply);
- BpGraphicBufferProducer.dequeueBuffer【接口層】
二、進程間圖傳遞圖形buffer詳解
【1】SurfaceFlinger進程 和 IAllocator 服務(wù)之間傳遞圖形顯示的Buffer
IAllocator 服務(wù)全稱為 android.hardware.graphics.allocator@4.0::IAllocator/default
高通平臺上的進程名為:vendor.qti.hardware.display.allocator-service
SurfaceFlinger IAllocator 接口的 allocate 函數(shù)
// frameworks/native/libs/ui/Gralloc4.cpp status_t Gralloc4Allocator::allocate(std::string requestorName, uint32_t width, uint32_t height, android::PixelFormat format, uint32_t layerCount, uint64_t usage, uint32_t bufferCount, uint32_t* outStride, buffer_handle_t* outBufferHandles, bool importBuffers) const { //... //===================關(guān)鍵代碼============ auto ret = mAllocator->allocate(descriptor, bufferCount, [&](const auto& tmpError, const auto& tmpStride, const auto& tmpBuffers) {// const auto& tmpBuffers 是個 hidl_handle 類型 error = static_cast<status_t>(tmpError); if (tmpError != Error::NONE) { return; } if (importBuffers) { for (uint32_t i = 0; i < bufferCount; i++) { error = mMapper.importBuffer(tmpBuffers[i], &outBufferHandles[i]); if (error != NO_ERROR) { for (uint32_t j = 0; j < i; j++) { mMapper.freeBuffer(outBufferHandles[j]); outBufferHandles[j] = nullptr; } return; } } } else { //.... } *outStride = tmpStride; }); //... return (ret.isOk()) ? error : static_cast<status_t>(kTransactionError); }
allocator服務(wù)端的hidl接口實現(xiàn)
不看具體的allocate函數(shù)實現(xiàn),重點看數(shù)據(jù)傳輸過程
//out/soong/.intermediates/hardware/interfaces/graphics/allocator/4.0/android.hardware.graphics.allocator@4.0_genc++/gen/android/hardware/graphics/allocator/4.0/AllocatorAll.cpp // 這部分代碼是 hidl 接口編譯完成后,out目錄自動生成的代碼,源碼目錄下沒有 // Methods from ::android::hardware::graphics::allocator::V4_0::IAllocator follow. ::android::status_t BnHwAllocator::_hidl_allocate( ::android::hidl::base::V1_0::BnHwBase* _hidl_this, const ::android::hardware::Parcel &_hidl_data, ::android::hardware::Parcel *_hidl_reply, TransactCallback _hidl_cb) { //... //========================調(diào)用服務(wù)端真正的實現(xiàn)===================== ::android::hardware::Return<void> _hidl_ret = static_cast<IAllocator*>(_hidl_this->getImpl().get())->allocate(*descriptor, count, [&](const auto &_hidl_out_error, const auto &_hidl_out_stride, const auto &_hidl_out_buffers) { if (_hidl_callbackCalled) { LOG_ALWAYS_FATAL("allocate: _hidl_cb called a second time, but must be called once."); } _hidl_callbackCalled = true; //===============函數(shù)調(diào)用完成后,開始寫返回數(shù)據(jù)======================== ::android::hardware::writeToParcel(::android::hardware::Status::ok(), _hidl_reply); _hidl_err = _hidl_reply->writeInt32((int32_t)_hidl_out_error); if (_hidl_err != ::android::OK) { goto _hidl_error; } // 返回數(shù)據(jù) tmpStride 的值 _hidl_err = _hidl_reply->writeUint32(_hidl_out_stride); if (_hidl_err != ::android::OK) { goto _hidl_error; } size_t _hidl__hidl_out_buffers_parent; _hidl_err = _hidl_reply->writeBuffer(&_hidl_out_buffers, sizeof(_hidl_out_buffers), &_hidl__hidl_out_buffers_parent); if (_hidl_err != ::android::OK) { goto _hidl_error; } size_t _hidl__hidl_out_buffers_child; _hidl_err = ::android::hardware::writeEmbeddedToParcel( _hidl_out_buffers, _hidl_reply, _hidl__hidl_out_buffers_parent, 0 /* parentOffset */, &_hidl__hidl_out_buffers_child); if (_hidl_err != ::android::OK) { goto _hidl_error; } //關(guān)鍵代碼====傳輸上邊的回調(diào)函數(shù)的參數(shù) const auto& tmpBuffers 的每個元素, 數(shù)據(jù)類型是 hidl_handle 類型 for (size_t _hidl_index_0 = 0; _hidl_index_0 < _hidl_out_buffers.size(); ++_hidl_index_0) { // 關(guān)鍵函數(shù) android::hardware::writeEmbeddedToParcel _hidl_err = ::android::hardware::writeEmbeddedToParcel( _hidl_out_buffers[_hidl_index_0], _hidl_reply, _hidl__hidl_out_buffers_child, _hidl_index_0 * sizeof(::android::hardware::hidl_handle)); if (_hidl_err != ::android::OK) { goto _hidl_error; } } //... if (_hidl_err != ::android::OK) { return; } _hidl_cb(*_hidl_reply); }); _hidl_ret.assertOk(); if (!_hidl_callbackCalled) { LOG_ALWAYS_FATAL("allocate: _hidl_cb not called, but must be called once."); } return _hidl_err; }
android::hardware::writeEmbeddedToParcel
// system/libhidl/transport/HidlBinderSupport.cpp status_t writeEmbeddedToParcel(const hidl_handle &handle, Parcel *parcel, size_t parentHandle, size_t parentOffset) { //此處調(diào)用了 hwbinder/Parcel.cpp 的writeEmbeddedNativeHandle 函數(shù) status_t _hidl_err = parcel->writeEmbeddedNativeHandle( handle.getNativeHandle(), parentHandle, parentOffset + hidl_handle::kOffsetOfNativeHandle); return _hidl_err; } // system/libhwbinder/Parcel.cpp status_t Parcel::writeEmbeddedNativeHandle(const native_handle_t *handle, size_t parent_buffer_handle, size_t parent_offset) { return writeNativeHandleNoDup(handle, true /* embedded */, parent_buffer_handle, parent_offset); } status_t Parcel::writeNativeHandleNoDup(const native_handle_t *handle, bool embedded, size_t parent_buffer_handle, size_t parent_offset) { //... struct binder_fd_array_object fd_array { .hdr = { .type = BINDER_TYPE_FDA }, // 關(guān)鍵代碼: BINDER_TYPE_FDA 類型,binder內(nèi)核驅(qū)動代碼對這個類型有專門的處理 .num_fds = static_cast<binder_size_t>(handle->numFds), .parent = buffer_handle, .parent_offset = offsetof(native_handle_t, data), }; return writeObject(fd_array); }
之后的代碼,見 binder驅(qū)動對 BINDER_TYPE_FDA 、BINDER_TYPE_FD 類型的處理
【2】App進程同 SurfaceFlinger 進程之間傳遞 GraphicBuffer 對象
GraphicBuffer 對象
服務(wù)端 requestBuffer 流程
// frameworks/native/libs/gui/IGraphicBufferProducer.cpp status_t BnGraphicBufferProducer::onTransact( uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags) { switch(code) { case REQUEST_BUFFER: { CHECK_INTERFACE(IGraphicBufferProducer, data, reply); int bufferIdx = data.readInt32(); sp<GraphicBuffer> buffer; int result = requestBuffer(bufferIdx, &buffer); reply->writeInt32(buffer != nullptr); if (buffer != nullptr) { reply->write(*buffer);// GraphicBuffer 對象回寫========!!!!!!!!!!!!!!===== } reply->writeInt32(result); return NO_ERROR; } //... } //... }
Parcel::write 寫對象流程,
Parcel::write Parcel.h
// frameworks/native/libs/binder/include/binder/Parcel.h template<typename T> status_t Parcel::write(const Flattenable<T>& val) {// 對象需要繼承 Flattenable const FlattenableHelper<T> helper(val); return write(helper); }
Parcel::write Parcel.cpp
// frameworks/native/libs/binder/Parcel.cpp status_t Parcel::write(const FlattenableHelperInterface& val) { status_t err; // size if needed const size_t len = val.getFlattenedSize(); // val.getFdCount(); 這個值為 GraphicBuffer.mTransportNumFds // 從這個接口獲取 // GrallocMapper::getTransportSize(buffer_handle_t bufferHandle, uint32_t* outNumFds, uint32_t* outNumInts) const size_t fd_count = val.getFdCount();// 這個值為 GraphicBuffer.mTransportNumFds //........... // 調(diào)用對象的 flatten 寫到緩存中 err = val.flatten(buf, len, fds, fd_count); // fd_count 不為0,需要寫 fd for (size_t i=0 ; i<fd_count && err==NO_ERROR ; i++) { err = this->writeDupFileDescriptor( fds[i] ); } if (fd_count) { delete [] fds; } return err; }
Parcel::writeDupFileDescriptor 寫fd流程
// frameworks/native/libs/binder/Parcel.cpp status_t Parcel::writeDupFileDescriptor(int fd) { int dupFd; if (status_t err = dupFileDescriptor(fd, &dupFd); err != OK) { return err; } //=============!!!!!!!!!!!!!=========== status_t err = writeFileDescriptor(dupFd, true /*takeOwnership*/); if (err != OK) { close(dupFd); } return err; } status_t Parcel::writeFileDescriptor(int fd, bool takeOwnership) { //........ #ifdef BINDER_WITH_KERNEL_IPC // frameworks/native/libs/binder/Android.bp 中定義了此宏 "-DBINDER_WITH_KERNEL_IPC", flat_binder_object obj; obj.hdr.type = BINDER_TYPE_FD;// 類型為 fd ,內(nèi)核會自動創(chuàng)建fd obj.flags = 0; obj.binder = 0; /* Don't pass uninitialized stack data to a remote process */ obj.handle = fd; obj.cookie = takeOwnership ? 1 : 0; return writeObject(obj, true); #else // BINDER_WITH_KERNEL_IPC LOG_ALWAYS_FATAL("Binder kernel driver disabled at build time"); (void)fd; (void)takeOwnership; return INVALID_OPERATION; #endif // BINDER_WITH_KERNEL_IPC }
之后的代碼,見 binder驅(qū)動對 BINDER_TYPE_FDA 、BINDER_TYPE_FD 類型的處理
【3】linux內(nèi)核部分,binder驅(qū)動對 BINDER_TYPE_FDA 、BINDER_TYPE_FD 類型的處理
binder_transaction
// 這里使用的 3.8 的內(nèi)核版本,邏輯較為清晰 // 更新的內(nèi)核版本需要看 binder_apply_fd_fixups 函數(shù)部分 // https://android.googlesource.com/kernel/msm/+/refs/heads/android-msm-coral-4.14-android10/drivers/android/binder.c static void binder_transaction(struct binder_proc *proc, struct binder_thread *thread, struct binder_transaction_data *tr, int reply, binder_size_t extra_buffers_size) { //... case BINDER_TYPE_FD: { struct binder_fd_object *fp = to_binder_fd_object(hdr); //數(shù)據(jù)類型為 BINDER_TYPE_FD 時,調(diào)用了 binder_translate_fd int target_fd = binder_translate_fd(fp->fd, t, thread, in_reply_to); if (target_fd < 0) { return_error = BR_FAILED_REPLY; return_error_param = target_fd; return_error_line = __LINE__; goto err_translate_failed; } fp->pad_binder = 0; fp->fd = target_fd; binder_alloc_copy_to_buffer(&target_proc->alloc, t->buffer, object_offset, fp, sizeof(*fp)); } break; case BINDER_TYPE_FDA: { struct binder_object ptr_object; binder_size_t parent_offset; struct binder_fd_array_object *fda = to_binder_fd_array_object(hdr); size_t num_valid = (buffer_offset - off_start_offset) / sizeof(binder_size_t); struct binder_buffer_object *parent = binder_validate_ptr(target_proc, t->buffer, &ptr_object, fda->parent, off_start_offset, &parent_offset, num_valid); if (!parent) { binder_user_error("%d:%d got transaction with invalid parent offset or type\n", proc->pid, thread->pid); return_error = BR_FAILED_REPLY; return_error_param = -EINVAL; return_error_line = __LINE__; goto err_bad_parent; } if (!binder_validate_fixup(target_proc, t->buffer, off_start_offset, parent_offset, fda->parent_offset, last_fixup_obj_off, last_fixup_min_off)) { binder_user_error("%d:%d got transaction with out-of-order buffer fixup\n", proc->pid, thread->pid); return_error = BR_FAILED_REPLY; return_error_param = -EINVAL; return_error_line = __LINE__; goto err_bad_parent; } //數(shù)據(jù)類型為 BINDER_TYPE_FDA 時,調(diào)用了 binder_translate_fd ret = binder_translate_fd_array(fda, parent, t, thread, in_reply_to); if (ret < 0) { return_error = BR_FAILED_REPLY; return_error_param = ret; return_error_line = __LINE__; goto err_translate_failed; } last_fixup_obj_off = parent_offset; last_fixup_min_off = fda->parent_offset + sizeof(u32) * fda->num_fds; } break; //... }
binder_translate_fd_array 函數(shù)中對每一個fd都調(diào)用了 binder_translate_fd 函數(shù)
binder_translate_fd
static int binder_translate_fd(int fd, struct binder_transaction *t, struct binder_thread *thread, struct binder_transaction *in_reply_to) { struct binder_proc *proc = thread->proc; struct binder_proc *target_proc = t->to_proc; int target_fd; struct file *file; int ret; bool target_allows_fd; if (in_reply_to) target_allows_fd = !!(in_reply_to->flags & TF_ACCEPT_FDS); else target_allows_fd = t->buffer->target_node->accept_fds; if (!target_allows_fd) { binder_user_error("%d:%d got %s with fd, %d, but target does not allow fds\n", proc->pid, thread->pid, in_reply_to ? "reply" : "transaction", fd); ret = -EPERM; goto err_fd_not_accepted; } file = fget(fd);//從fd獲取 file 對象 if (!file) { binder_user_error("%d:%d got transaction with invalid fd, %d\n", proc->pid, thread->pid, fd); ret = -EBADF; goto err_fget; } //se權(quán)限處理 ret = security_binder_transfer_file(proc->tsk, target_proc->tsk, file); if (ret < 0) { ret = -EPERM; goto err_security; } //在目標進程中找到一個可用的fd target_fd = task_get_unused_fd_flags(target_proc, O_CLOEXEC); if (target_fd < 0) { ret = -ENOMEM; goto err_get_unused_fd; } // 調(diào)用task_fd_install將 file對象 關(guān)聯(lián)到目標進程中的fd task_fd_install(target_proc, target_fd, file); trace_binder_transaction_fd(t, fd, target_fd); binder_debug(BINDER_DEBUG_TRANSACTION, " fd %d -> %d\n", fd, target_fd); return target_fd; err_get_unused_fd: err_security: fput(file); err_fget: err_fd_not_accepted: return ret; }
附、圖形緩存的幾個重要數(shù)據(jù)類型
1、App端 Surface 同 SurfaceFlinger 用于傳遞共享內(nèi)存 fd 的對象 GraphicBuffer
GraphicBuffer
// frameworks/native/libs/ui/include/ui/GraphicBuffer.h class GraphicBuffer : public ANativeObjectBase<ANativeWindowBuffer, GraphicBuffer, RefBase>, public Flattenable<GraphicBuffer> { //... status_t flatten(void*& buffer, size_t& size, int*& fds, size_t& count) const; status_t unflatten(void const*& buffer, size_t& size, int const*& fds, size_t& count); //... } // frameworks/native/libs/ui/include/ui/ANativeObjectBase.h /* * This helper class turns a ANativeXXX object type into a C++ * reference-counted object; with proper type conversions. */ template <typename NATIVE_TYPE, typename TYPE, typename REF, typename NATIVE_BASE = android_native_base_t> class ANativeObjectBase : public NATIVE_TYPE, public REF { //... } //轉(zhuǎn)換后: class ANativeObjectBase : public ANativeWindowBuffer, public RefBase { //... }
- GraphicBuffer 繼承 ANativeWindowBuffer Flattenable
- Flattenable 兩個關(guān)鍵函數(shù) flatten unflatten,用于binder序列化時使用。
ANativeWindowBuffer
// /frameworks/native/libs/nativebase/include/nativebase/nativebase.h // 圖形Buffer的Size = stride * height * 每像素字節(jié)數(shù) typedef struct ANativeWindowBuffer { ... int width; // 圖形Buffer的寬度 int height; // 圖形Buffer的高度 int stride; // 圖形Buffer的步長,為了處理對齊問題,與width可能不同 int format; // 圖形Buffer的像素格式 const native_handle_t* handle; // 指向一塊圖形Buffer uint64_t usage; // 圖形Buffer的使用規(guī)則(gralloc會分配不同屬性的圖形Buffer) ... } ANativeWindowBuffer_t;
native_handle_t
// system/core/libcutils/include/cutils/native_handle.h typedef struct native_handle { int version; /* sizeof(native_handle_t) */ // //data[0]中的文件描述符個數(shù) int numFds; /* number of file-descriptors at &data[0] */ // //&data[numFds]中int的個數(shù) int numInts; /* number of ints at &data[numFds] */ int data[0]; /* numFds + numInts ints */ } native_handle_t;
buffer_handle_t 同 native_handle_t
// system/core/libcutils/include/cutils/native_handle.h typedef const native_handle_t* buffer_handle_t;
2、hidl接口 進程間傳遞 fd 使用的數(shù)據(jù)類型 (HWbinder 傳遞 fd 的對象)
- hidl_handle 用于 SurfaceFlinger 同 IAllocator HIDL接口的服務(wù)之間傳遞 共享內(nèi)存fd
- 高通平臺上,這個 HIDL 服務(wù)端對應(yīng)的進程是 vendor.qti.hardware.display.allocator-service
hidl_handle
struct hidl_handle { hidl_handle(); ~hidl_handle(); hidl_handle(const native_handle_t *handle); // copy constructor. hidl_handle(const hidl_handle &other); // move constructor. hidl_handle(hidl_handle &&other) noexcept; // assignment operators hidl_handle &operator=(const hidl_handle &other); hidl_handle &operator=(const native_handle_t *native_handle); hidl_handle &operator=(hidl_handle &&other) noexcept; void setTo(native_handle_t* handle, bool shouldOwn = false); const native_handle_t* operator->() const; // implicit conversion to const native_handle_t* operator const native_handle_t *() const; // explicit conversion const native_handle_t *getNativeHandle() const; // offsetof(hidl_handle, mHandle) exposed since mHandle is private. static const size_t kOffsetOfNativeHandle; private: void freeHandle(); // 核心數(shù)據(jù) native_handle_t mHandle; details::hidl_pointer<const native_handle_t> mHandle; bool mOwnsHandle; uint8_t mPad[7]; };
總結(jié):
- SurfaceFlinger進程 和 IAllocator服務(wù)進程之間通過 hidl_handle 類型的數(shù)據(jù)傳遞 圖形buffer共享內(nèi)存的fd
- 數(shù)據(jù)傳輸中對 hidl_handle 類型數(shù)據(jù)特化處理,并把binder數(shù)據(jù)類型設(shè)置為 BINDER_TYPE_FDA
- binder內(nèi)核對 BINDER_TYPE_FDA 類型數(shù)據(jù)特化處理
- 同時在 IAllocator.allocate 的回調(diào)函數(shù)中調(diào)用 IMapper.importBuffer 把內(nèi)存映射到當前進程
- App進程 同 SurfaceFlinger進程之間使用 GraphicBuffer 對象傳遞 圖形buffer共享內(nèi)存的fd
- 數(shù)據(jù)傳輸中對 GraphicBuffer 中的 native_handle_t 數(shù)據(jù)特化處理,并把binder數(shù)據(jù)類型設(shè)置為 BINDER_TYPE_FD
- binder內(nèi)核對 BINDER_TYPE_FD 類型數(shù)據(jù)特化處理
- 同時在從binder讀取數(shù)據(jù)創(chuàng)建GraphicBuffer對象時,調(diào)用 GraphicBuffer.unflatten,內(nèi)部調(diào)用 IMapper.importBuffer 把內(nèi)存映射到當前進程
后記
Android12 之后使用 BLASTBufferQueue ,雖然有些變化,但是理解了 GraphicBuffer 和 hidl_handle 傳遞 fd 的過程,這些都游刃有余
Android 的 aidl接口層、hidl接口層、binder bp 接口層 都隱藏了很多關(guān)鍵代碼,導(dǎo)致看代碼時,感覺總是云里霧里
- 像hidl接口,生成的大量代碼,在out/soong目錄下,僅僅看源碼樹目錄下的代碼根本找不到好吧。
以上就是清楚詳解Android 進程間圖傳遞圖形buffer原理的詳細內(nèi)容,更多關(guān)于Android 進程間圖傳遞圖形buffer的資料請關(guān)注腳本之家其它相關(guān)文章!
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