Android Gralloc模块分析--深入分析

前一篇的文章《Android Gralloc模块分析》从功能的角度分析了Gralloc模块，基本掌握了Gralloc的总体结构，但是具体函数还有待进一步学习与分析。它们包括：

      

分别对应gralloc.cpp、framebuffer.cpp、mapper.cpp

这里的组织感觉不太合理，应该改成：gralloc_module.cpp跟映射相关、alloc_device.cpp跟分配图形缓冲区相关、framebuffer_device.cpp跟渲染相关。今天看了瑞星微的gralloc代码，组织得就很好，逻辑性强。

回顾

        上一篇文章提到，模块在被框架层加载后，就导出了HMI符号地址对应的hw_module_t结构。实际上导出了

        gralloc_device_open方法

        gralloc_register_buffer方法

        其中后者用来将图形缓冲区映射进程地址空间中；而前者用来打开两个设备，这两个设备分别是alloc_device_t和framebuffer_device_t，它们返回了主要函数有：

        gralloc_alloc方法

         fb_post方法

        上面两种方法，分别用来分配图形缓冲区，渲染帧缓冲区。本文下面的内容具体分析这些函数及相关的函数。

gralloc设备                                                                             gralloc.cpp

/* * Copyright (C) 2008 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */#include <limits.h>#include <unistd.h>#include <fcntl.h>#include <errno.h>#include <pthread.h>#include <stdlib.h>#include <string.h>#include <sys/mman.h>#include <sys/stat.h>#include <sys/types.h>#include <sys/ioctl.h>#include <cutils/ashmem.h>#include <cutils/log.h>#include <cutils/atomic.h>#include <hardware/hardware.h>#include <hardware/gralloc.h>#include "gralloc_priv.h"#include "gr.h"/*****************************************************************************/struct gralloc_context_t {    alloc_device_t  device;    /* our private data here */};static int gralloc_alloc_buffer(alloc_device_t* dev,        size_t size, int usage, buffer_handle_t* pHandle);/*****************************************************************************/int fb_device_open(const hw_module_t* module, const char* name,        hw_device_t** device);static int gralloc_device_open(const hw_module_t* module, const char* name,        hw_device_t** device);extern int gralloc_lock(gralloc_module_t const* module,        buffer_handle_t handle, int usage,        int l, int t, int w, int h,        void** vaddr);extern int gralloc_unlock(gralloc_module_t const* module,         buffer_handle_t handle);extern int gralloc_register_buffer(gralloc_module_t const* module,        buffer_handle_t handle);extern int gralloc_unregister_buffer(gralloc_module_t const* module,        buffer_handle_t handle);/*****************************************************************************///模块被加载后，会执行的open方法，用来打开设备static struct hw_module_methods_t gralloc_module_methods = {        open: gralloc_device_open};// 导出符号HMI，是HAL框架编程规范定义的struct private_module_t HAL_MODULE_INFO_SYM = {    base: {        common: {            tag: HARDWARE_MODULE_TAG,            version_major: 1,            version_minor: 0,            id: GRALLOC_HARDWARE_MODULE_ID,            name: "Graphics Memory Allocator Module",            author: "The Android Open Source Project",            methods: &gralloc_module_methods        },        registerBuffer: gralloc_register_buffer,        unregisterBuffer: gralloc_unregister_buffer,        lock: gralloc_lock,        unlock: gralloc_unlock,    },    framebuffer: 0,    flags: 0,    numBuffers: 0,    bufferMask: 0,    lock: PTHREAD_MUTEX_INITIALIZER,    currentBuffer: 0,};/*****************************************************************************///帧缓冲区锁定后的操作，在帧缓冲区找一个空闲的图形缓冲区，记录到private_handle_t结构中并返回// dev :gralloc设备// size:整个图像所占用的字节数// usage:图形缓冲区位置标志位：fb、内存// pHandle: 图形缓冲区描述符static int gralloc_alloc_framebuffer_locked(alloc_device_t* dev,        size_t size, int usage, buffer_handle_t* pHandle){//将至类型转化，hw_module_t转化为private_module_t    private_module_t* m = reinterpret_cast<private_module_t*>(            dev->common.module);    // allocate the framebuffer    if (m->framebuffer == NULL) { //帧缓冲区没有被初始化        // initialize the framebuffer, the framebuffer is mapped once        // and forever.// 初始化帧缓冲区，映射到当前的进程的虚拟地址空间中来        int err = mapFrameBufferLocked(m);        if (err < 0) {            return err;        }    }//得到帧缓冲区使用情况    const uint32_t bufferMask = m->bufferMask;//得到帧缓冲区划分为多少个图形缓冲区使用    const uint32_t numBuffers = m->numBuffers;//设备显示器显示一屏图形所占用的内存大小    const size_t bufferSize = m->finfo.line_length * m->info.yres;    if (numBuffers == 1) {        // If we have only one buffer, we never use page-flipping. Instead,        // we return a regular buffer which will be memcpy'ed to the main        // screen when post is called.//不能再帧缓冲区中分配，就在内存中分配图形缓冲区        int newUsage = (usage & ~GRALLOC_USAGE_HW_FB) | GRALLOC_USAGE_HW_2D;        return gralloc_alloc_buffer(dev, bufferSize, newUsage, pHandle);    }//系统帧缓冲区中的图形缓冲区都被分配出去了    if (bufferMask >= ((1LU<<numBuffers)-1)) {        // We ran out of buffers.        return -ENOMEM;    }//指向系统缓冲区的基址    // create a "fake" handles for it    intptr_t vaddr = intptr_t(m->framebuffer->base);//创建一个private_handle_t来描述一个将要分配出去的图形缓冲区    private_handle_t* hnd = new private_handle_t(dup(m->framebuffer->fd), size,            private_handle_t::PRIV_FLAGS_FRAMEBUFFER);//找帧缓冲区中一个空闲的图形缓冲区    // find a free slot    for (uint32_t i=0 ; i<numBuffers ; i++) {        if ((bufferMask & (1LU<<i)) == 0) {            m->bufferMask |= (1LU<<i);            break;        }//每次查找偏移一个图形缓冲区的大小        vaddr += bufferSize;    }    //分配出去的图形缓冲区的基地址保存在private_handle_t的base变量中    hnd->base = vaddr;//相对于帧缓冲区的基地址偏移保存在private_handle_t的offset变量中    hnd->offset = vaddr - intptr_t(m->framebuffer->base);//返回private_handle_t这个图形缓冲区描述符    *pHandle = hnd;    return 0;}/*****************************************************************************///1.在帧缓冲区中分配图形缓冲区// dev :gralloc设备// size:整个图像所占用的字节数// usage:图形缓冲区位置标志位：fb、内存// pHandle: 图形缓冲区描述符static int gralloc_alloc_framebuffer(alloc_device_t* dev,        size_t size, int usage, buffer_handle_t* pHandle){//将至类型转化，hw_module_t转化为private_module_t    private_module_t* m = reinterpret_cast<private_module_t*>(            dev->common.module);//并发问题加锁    pthread_mutex_lock(&m->lock);    int err = gralloc_alloc_framebuffer_locked(dev, size, usage, pHandle); //锁定帧缓冲区后操作    pthread_mutex_unlock(&m->lock);    return err;}/*****************************************************************************///2.在内存中分配图形缓冲区// dev :gralloc设备// size:整个图像所占用的字节数// usage:图形缓冲区位置标志位：fb、内存// pHandle: 图形缓冲区描述符static int gralloc_alloc_buffer(alloc_device_t* dev,        size_t size, int usage, buffer_handle_t* pHandle){    int err = 0;    int fd = -1;//字节大小转化到页大小    size = roundUpToPageSize(size);    //创建匿名内存区域    fd = ashmem_create_region("gralloc-buffer", size);    if (fd < 0) {        ALOGE("couldn't create ashmem (%s)", strerror(-errno));        err = -errno;    }//创建成功后，分配一个private_handle_t用来记录图形缓冲区，并返回给调用者    if (err == 0) {        private_handle_t* hnd = new private_handle_t(fd, size, 0);        gralloc_module_t* module = reinterpret_cast<gralloc_module_t*>(                dev->common.module);//映射图形缓冲区到进程的虚拟地址空间中，帧缓冲区中分配时也映射了噢        err = mapBuffer(module, hnd);        if (err == 0) {            *pHandle = hnd;        }    }        ALOGE_IF(err, "gralloc failed err=%s", strerror(-err));        return err;}/*****************************************************************************///用来分配图形缓冲区// int w : 图形缓冲区所保存图像的宽度，即一行多少个像素点// int h : 图形缓冲区所保存图像的高度，即一共有多少行// format: 表示图形的格式// usage : 标志位，GRALLOC_USAGE_HW_FB值表示在帧缓冲区中分配图形缓冲区// pHandle: 图形缓冲区句柄，用来描述一个图形缓冲区// pStride: 用来返回一行的像素点个数static int gralloc_alloc(alloc_device_t* dev,        int w, int h, int format, int usage,        buffer_handle_t* pHandle, int* pStride){    if (!pHandle || !pStride)        return -EINVAL;    size_t size, stride;    int align = 4;    int bpp = 0;    //每个像素点多少字节    switch (format) {        case HAL_PIXEL_FORMAT_RGBA_8888:        case HAL_PIXEL_FORMAT_RGBX_8888:        case HAL_PIXEL_FORMAT_BGRA_8888:            bpp = 4;            break;        case HAL_PIXEL_FORMAT_RGB_888:            bpp = 3;            break;        case HAL_PIXEL_FORMAT_RGB_565:        case HAL_PIXEL_FORMAT_RGBA_5551:        case HAL_PIXEL_FORMAT_RGBA_4444:        case HAL_PIXEL_FORMAT_RAW_SENSOR:            bpp = 2;            break;        default:            return -EINVAL;    }//将一行所占的字节数对齐到4个字节，例如：2013对齐到四个字节会变为2016    size_t bpr = (w*bpp + (align-1)) & ~(align-1);//对齐后乘以高度，表示整个图像所占的字节数    size = bpr * h;//stride表示一行的像素点个数    stride = bpr / bpp;    int err;    if (usage & GRALLOC_USAGE_HW_FB) {//在帧缓冲区中分配图形缓冲区        err = gralloc_alloc_framebuffer(dev, size, usage, pHandle);    } else {//内存中分配图形缓冲区        err = gralloc_alloc_buffer(dev, size, usage, pHandle);    }    if (err < 0) {        return err;    }//返回一行的像素点个数    *pStride = stride;    return 0;}/*****************************************************************************///用来释放图形缓冲区static int gralloc_free(alloc_device_t* dev,        buffer_handle_t handle){    if (private_handle_t::validate(handle) < 0)        return -EINVAL;    private_handle_t const* hnd = reinterpret_cast<private_handle_t const*>(handle);//图形缓冲区在帧缓冲区分配    if (hnd->flags & private_handle_t::PRIV_FLAGS_FRAMEBUFFER) {        // free this buffer        private_module_t* m = reinterpret_cast<private_module_t*>(                dev->common.module);//计算该图形缓冲区的大小        const size_t bufferSize = m->finfo.line_length * m->info.yres;        int index = (hnd->base - m->framebuffer->base) / bufferSize;//图形缓冲区使用情况记录到buffer屏蔽位中        m->bufferMask &= ~(1<<index);     } else { //图形缓冲区是匿名内存        gralloc_module_t* module = reinterpret_cast<gralloc_module_t*>(                dev->common.module);//在mapper.cpp中实现的        terminateBuffer(module, const_cast<private_handle_t*>(hnd));    }    close(hnd->fd);    delete hnd;    return 0;}/*****************************************************************************/static int gralloc_close(struct hw_device_t *dev){    gralloc_context_t* ctx = reinterpret_cast<gralloc_context_t*>(dev);    if (ctx) {        /* TODO: keep a list of all buffer_handle_t created, and free them         * all here.         */        free(ctx);    }    return 0;}//模块的入口函数，用来打开gralloc设备、fb设备int gralloc_device_open(const hw_module_t* module, const char* name,        hw_device_t** device){    int status = -EINVAL;//1. 打开gralloc设备    if (!strcmp(name, GRALLOC_HARDWARE_GPU0)) {        gralloc_context_t *dev;//对gralloc设备的封装结构        dev = (gralloc_context_t*)malloc(sizeof(*dev));        /* initialize our state here */        memset(dev, 0, sizeof(*dev));        /* initialize the procs */        dev->device.common.tag = HARDWARE_DEVICE_TAG;        dev->device.common.version = 0;        dev->device.common.module = const_cast<hw_module_t*>(module);        dev->device.common.close = gralloc_close;//gralloc封装的主要方法gralloc_alloc,用来分配图形缓冲区        dev->device.alloc   = gralloc_alloc;        dev->device.free    = gralloc_free;//设备指针返回给框架层，即封装方法返回给框架层        *device = &dev->device.common;        status = 0;    } else {//2. 打开fb设备        status = fb_device_open(module, name, device);    }    return status;}

fb设备

/* * Copyright (C) 2008 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */#include <sys/mman.h>#include <dlfcn.h>#include <cutils/ashmem.h>#include <cutils/log.h>#include <hardware/hardware.h>#include <hardware/gralloc.h>#include <fcntl.h>#include <errno.h>#include <sys/ioctl.h>#include <string.h>#include <stdlib.h>#include <cutils/log.h>#include <cutils/atomic.h>#if HAVE_ANDROID_OS#include <linux/fb.h>#endif#include "gralloc_priv.h"#include "gr.h"/*****************************************************************************/// numbers of buffers for page flipping#define NUM_BUFFERS 2enum {    PAGE_FLIP = 0x00000001,    LOCKED = 0x00000002};struct fb_context_t {    framebuffer_device_t  device;};/*****************************************************************************///检查两个图形缓冲区渲染到帧缓冲区的间隔时间是否合法static int fb_setSwapInterval(struct framebuffer_device_t* dev,            int interval){    fb_context_t* ctx = (fb_context_t*)dev;    if (interval < dev->minSwapInterval || interval > dev->maxSwapInterval)        return -EINVAL;    // FIXME: implement fb_setSwapInterval    return 0;}//设置可以更新的区域，放在fix_var_screeninfo的保留字段当中static int fb_setUpdateRect(struct framebuffer_device_t* dev,        int l, int t, int w, int h){    if (((w|h) <= 0) || ((l|t)<0))        return -EINVAL;            fb_context_t* ctx = (fb_context_t*)dev;    private_module_t* m = reinterpret_cast<private_module_t*>(            dev->common.module);    m->info.reserved[0] = 0x54445055; // "UPDT";    m->info.reserved[1] = (uint16_t)l | ((uint32_t)t << 16);    m->info.reserved[2] = (uint16_t)(l+w) | ((uint32_t)(t+h) << 16);    return 0;}//用来渲染图形缓冲区数据到系统缓冲区// dev :fb设备// buffer:图形缓冲区描述符static int fb_post(struct framebuffer_device_t* dev, buffer_handle_t buffer){    if (private_handle_t::validate(buffer) < 0)        return -EINVAL;    fb_context_t* ctx = (fb_context_t*)dev;    private_handle_t const* hnd = reinterpret_cast<private_handle_t const*>(buffer);    private_module_t* m = reinterpret_cast<private_module_t*>(            dev->common.module);//若是该图形缓冲区时在帧缓冲区中分配的    if (hnd->flags & private_handle_t::PRIV_FLAGS_FRAMEBUFFER) {//图形缓冲区在帧缓冲区中，是不需要拷贝的，但是需要告诉帧缓冲区设备，这个图形缓冲区是要输出的图形缓冲区        const size_t offset = hnd->base - m->framebuffer->base;//表示下一个垂直同步事件出现时，才将要输出的图形缓冲区绘制出来。这样避免了闪烁        m->info.activate = FB_ACTIVATE_VBL;        m->info.yoffset = offset / m->finfo.line_length;//用哪一个图形缓冲区，不用设置成员变量xoffset的值是因为所有的图形缓冲区的宽度是相等的//根据上面两个参数，设置帧缓冲区中绘制的图形缓冲区        if (ioctl(m->framebuffer->fd, FBIOPUT_VSCREENINFO, &m->info) == -1) {//设置输出缓冲区            ALOGE("FBIOPUT_VSCREENINFO failed");            m->base.unlock(&m->base, buffer);             return -errno;        }//记录当前被渲染的图形缓冲区        m->currentBuffer = buffer;            } else {//若图形缓冲区时在内存中分配的        // If we can't do the page_flip, just copy the buffer to the front         // FIXME: use copybit HAL instead of memcpy                void* fb_vaddr;        void* buffer_vaddr;        //锁定两个图形缓冲区，防止被改变。同时获取缓冲区的基地址        m->base.lock(&m->base, m->framebuffer,                 GRALLOC_USAGE_SW_WRITE_RARELY,                 0, 0, m->info.xres, m->info.yres,                &fb_vaddr);        m->base.lock(&m->base, buffer,                 GRALLOC_USAGE_SW_READ_RARELY,                 0, 0, m->info.xres, m->info.yres,                &buffer_vaddr);//参数1:图形缓冲区的起始地址   参数2:帧缓冲区的起始地址    参数3:一帧图形的大小（字节）        memcpy(fb_vaddr, buffer_vaddr, m->finfo.line_length * m->info.yres);        //解锁操作        m->base.unlock(&m->base, buffer);         m->base.unlock(&m->base, m->framebuffer);     }        return 0;}/*疑问: 这里为什么没有指定yoffset来指定系统缓冲区使用哪一个图形缓冲区呢。解答: 原来这里有个模式问题。      1.当虚拟屏幕的图形缓冲区只有一个时，是不支持PAGE_FLIP的，    这时分配的图形缓冲区必然在内存中，而帧缓冲区中输出的只有一个图形缓冲区  2.当虚拟屏幕的图形缓冲区有两个或以上是，才支持PAGE_FLIP,    这是分配的图形缓冲区就在帧缓冲区中，这样帧缓冲区才有选择哪一个输出的问题*//*****************************************************************************///获取帧缓冲区信息，映射到当前进程的虚拟地址空间中int mapFrameBufferLocked(struct private_module_t* module){//已经初始化完成    // already initialized...    if (module->framebuffer) {        return 0;    }     //设备文件枚举    char const * const device_template[] = {            "/dev/graphics/fb%u",            "/dev/fb%u",            0 };    int fd = -1;    int i=0;    char name[64];    while ((fd==-1) && device_template[i]) {//打开设备节点        snprintf(name, 64, device_template[i], 0);        fd = open(name, O_RDWR, 0);        i++;    }    if (fd < 0)        return -errno;//通过ioctl获取fb_fix_screeninfo信息    struct fb_fix_screeninfo finfo;    if (ioctl(fd, FBIOGET_FSCREENINFO, &finfo) == -1)        return -errno;//通过ioctl获取fb_var_screeninfo信息    struct fb_var_screeninfo info;    if (ioctl(fd, FBIOGET_VSCREENINFO, &info) == -1)        return -errno;    info.reserved[0] = 0;    info.reserved[1] = 0;    info.reserved[2] = 0;    info.xoffset = 0;    info.yoffset = 0;    info.activate = FB_ACTIVATE_NOW;    /*     * Request NUM_BUFFERS screens (at lest 2 for page flipping)     *///NUM_BUFFERS = 2,虚拟屏容纳两个可见屏，虚拟和可见的宽度值不变，高度前者是后者的整数倍    info.yres_virtual = info.yres * NUM_BUFFERS;//设置虚拟显示屏和像素格式    uint32_t flags = PAGE_FLIP;    if (ioctl(fd, FBIOPUT_VSCREENINFO, &info) == -1) {        info.yres_virtual = info.yres;        flags &= ~PAGE_FLIP;        ALOGW("FBIOPUT_VSCREENINFO failed, page flipping not supported");    }//若设置完毕后，若虚拟屏的高度小于可见屏的2倍，那么说明帧缓冲区不支持双图形缓冲区    if (info.yres_virtual < info.yres * 2) {        // we need at least 2 for page-flipping        info.yres_virtual = info.yres;        flags &= ~PAGE_FLIP;        ALOGW("page flipping not supported (yres_virtual=%d, requested=%d)",                info.yres_virtual, info.yres*2);    }//设置成功后再次或者fb_var_screen信息    if (ioctl(fd, FBIOGET_VSCREENINFO, &info) == -1)        return -errno;//计算刷新频率，先计算扫描一帧图形需要的时间//每个像素点扫描的时间为pixclock//一共有 ( info.upper_margin + info.lower_margin + info.yres ) * ( info.left_margin  + info.right_margin + info.xres ) 个像素点    uint64_t  refreshQuotient =    (            uint64_t( info.upper_margin + info.lower_margin + info.yres )            * ( info.left_margin  + info.right_margin + info.xres )            * info.pixclock    );    //求倒数得到1s钟能刷新的次数    /* Beware, info.pixclock might be 0 under emulation, so avoid a     * division-by-0 here (SIGFPE on ARM) */    int refreshRate = refreshQuotient > 0 ? (int)(1000000000000000LLU / refreshQuotient) : 0;//默认60HZ    if (refreshRate == 0) {        // bleagh, bad info from the driver        refreshRate = 60*1000;  // 60 Hz    }//dpi默认 160    if (int(info.width) <= 0 || int(info.height) <= 0) {        // the driver doesn't return that information        // default to 160 dpi        info.width  = ((info.xres * 25.4f)/160.0f + 0.5f);        info.height = ((info.yres * 25.4f)/160.0f + 0.5f);    }//每英寸像素点的个数，刷新频率计算    float xdpi = (info.xres * 25.4f) / info.width;    float ydpi = (info.yres * 25.4f) / info.height;    float fps  = refreshRate / 1000.0f;    ALOGI(   "using (fd=%d)\n"            "id           = %s\n"            "xres         = %d px\n"            "yres         = %d px\n"            "xres_virtual = %d px\n"            "yres_virtual = %d px\n"            "bpp          = %d\n"            "r            = %2u:%u\n"            "g            = %2u:%u\n"            "b            = %2u:%u\n",            fd,            finfo.id,            info.xres,            info.yres,            info.xres_virtual,            info.yres_virtual,            info.bits_per_pixel,            info.red.offset, info.red.length,            info.green.offset, info.green.length,            info.blue.offset, info.blue.length    );    ALOGI(   "width        = %d mm (%f dpi)\n"            "height       = %d mm (%f dpi)\n"            "refresh rate = %.2f Hz\n",            info.width,  xdpi,            info.height, ydpi,            fps    );//获取帧缓冲区的固定信息    if (ioctl(fd, FBIOGET_FSCREENINFO, &finfo) == -1)        return -errno;    if (finfo.smem_len <= 0)        return -errno;//记录到模块中    module->flags = flags;    module->info = info;    module->finfo = finfo;    module->xdpi = xdpi;    module->ydpi = ydpi;    module->fps = fps;    /*     * map the framebuffer     *///映射到帧缓冲区到应用程序的虚拟地址空间中    int err;//整个帧缓冲区的大小    size_t fbSize = roundUpToPageSize(finfo.line_length * info.yres_virtual);//分配描述符并记录到模块中，private_handle_t中的framebuffer结构用来描述帧缓冲区    module->framebuffer = new private_handle_t(dup(fd), fbSize, 0);//可以形成多少个图形缓冲区    module->numBuffers = info.yres_virtual / info.yres;    module->bufferMask = 0;//帧缓冲区的地址映射到虚拟地址空间中    void* vaddr = mmap(0, fbSize, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);    if (vaddr == MAP_FAILED) {        ALOGE("Error mapping the framebuffer (%s)", strerror(errno));        return -errno;    }//private_handle_t中的framebuffer结构中记录帧缓冲区的基址    module->framebuffer->base = intptr_t(vaddr);    memset(vaddr, 0, fbSize);    return 0;}static int mapFrameBuffer(struct private_module_t* module){//针对多线程并发问题加锁    pthread_mutex_lock(&module->lock);    int err = mapFrameBufferLocked(module);    pthread_mutex_unlock(&module->lock);    return err;}/*****************************************************************************/static int fb_close(struct hw_device_t *dev){    fb_context_t* ctx = (fb_context_t*)dev;    if (ctx) {        free(ctx);    }    return 0;}//fb设备的打开函数//module : 用来描述模块的//name   : 打开哪一个fb设备文件//device : 用来描述设备的int fb_device_open(hw_module_t const* module, const char* name,        hw_device_t** device){    int status = -EINVAL;    if (!strcmp(name, GRALLOC_HARDWARE_FB0)) {        /* initialize our state here *///fb设备的抽象封装结构        fb_context_t *dev = (fb_context_t*)malloc(sizeof(*dev));        memset(dev, 0, sizeof(*dev));        /* initialize the procs */        dev->device.common.tag = HARDWARE_DEVICE_TAG;        dev->device.common.version = 0;        dev->device.common.module = const_cast<hw_module_t*>(module);        dev->device.common.close = fb_close;//两个图形缓冲区渲染到帧缓冲区的间隔实现        dev->device.setSwapInterval = fb_setSwapInterval;//主要用来渲染图形缓冲区        dev->device.post            = fb_post;        dev->device.setUpdateRect = 0;    //获取帧缓冲区信息，并保存到m中        private_module_t* m = (private_module_t*)module;        status = mapFrameBuffer(m);//根据帧缓冲区信息来初始化alloc_device_t相关的结构        if (status >= 0) {            int stride = m->finfo.line_length / (m->info.bits_per_pixel >> 3);            int format = (m->info.bits_per_pixel == 32)                         ? HAL_PIXEL_FORMAT_RGBX_8888                         : HAL_PIXEL_FORMAT_RGB_565;            const_cast<uint32_t&>(dev->device.flags) = 0;            const_cast<uint32_t&>(dev->device.width) = m->info.xres;            const_cast<uint32_t&>(dev->device.height) = m->info.yres;            const_cast<int&>(dev->device.stride) = stride;            const_cast<int&>(dev->device.format) = format;            const_cast<float&>(dev->device.xdpi) = m->xdpi;            const_cast<float&>(dev->device.ydpi) = m->ydpi;            const_cast<float&>(dev->device.fps) = m->fps;            const_cast<int&>(dev->device.minSwapInterval) = 1;            const_cast<int&>(dev->device.maxSwapInterval) = 1;            *device = &dev->device.common;        }    }    return status;}

gralloc模块

/* * Copyright (C) 2008 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */#include <limits.h>#include <errno.h>#include <pthread.h>#include <unistd.h>#include <string.h>#include <sys/mman.h>#include <sys/stat.h>#include <sys/types.h>#include <cutils/log.h>#include <cutils/atomic.h>#include <hardware/hardware.h>#include <hardware/gralloc.h>#include "gralloc_priv.h"/* desktop Linux needs a little help with gettid() */#if defined(ARCH_X86) && !defined(HAVE_ANDROID_OS)#define __KERNEL__# include <linux/unistd.h>pid_t gettid() { return syscall(__NR_gettid);}#undef __KERNEL__#endif/*****************************************************************************///图形缓冲区的映射static int gralloc_map(gralloc_module_t const* module,        buffer_handle_t handle,        void** vaddr){    private_handle_t* hnd = (private_handle_t*)handle;//在内存中分配的话，需要映射到进程虚拟地址空间中，并需要计算图形缓冲区的在匿名内存中的基地址再返回    if (!(hnd->flags & private_handle_t::PRIV_FLAGS_FRAMEBUFFER)) {        size_t size = hnd->size;        void* mappedAddress = mmap(0, size,                PROT_READ|PROT_WRITE, MAP_SHARED, hnd->fd, 0);        if (mappedAddress == MAP_FAILED) {            ALOGE("Could not mmap %s", strerror(errno));            return -errno;        }        hnd->base = intptr_t(mappedAddress) + hnd->offset;        //ALOGD("gralloc_map() succeeded fd=%d, off=%d, size=%d, vaddr=%p",        //        hnd->fd, hnd->offset, hnd->size, mappedAddress);    }//在帧缓冲区中分配的话，是不需要计算的，因为在初始化帧缓冲区时已经做了    *vaddr = (void*)hnd->base;    return 0;}static int gralloc_unmap(gralloc_module_t const* module,        buffer_handle_t handle){    private_handle_t* hnd = (private_handle_t*)handle;//内存中    if (!(hnd->flags & private_handle_t::PRIV_FLAGS_FRAMEBUFFER)) {        void* base = (void*)hnd->base;        size_t size = hnd->size;        //ALOGD("unmapping from %p, size=%d", base, size);//注销图形缓冲区,与上面函数执行过程相反        if (munmap(base, size) < 0) {            ALOGE("Could not unmap %s", strerror(errno));        }    }//帧缓冲区中    hnd->base = 0;    return 0;}/*****************************************************************************/static pthread_mutex_t sMapLock = PTHREAD_MUTEX_INITIALIZER; /*****************************************************************************/// 关键调用gralloc_mapint gralloc_register_buffer(gralloc_module_t const* module,        buffer_handle_t handle){    if (private_handle_t::validate(handle) < 0)        return -EINVAL;    // if this handle was created in this process, then we keep it as is.    int err = 0;    private_handle_t* hnd = (private_handle_t*)handle;    if (hnd->pid != getpid()) {        void *vaddr;        err = gralloc_map(module, handle, &vaddr);    }    return err;}// 关键调用gralloc_unmapint gralloc_unregister_buffer(gralloc_module_t const* module,        buffer_handle_t handle){    if (private_handle_t::validate(handle) < 0)        return -EINVAL;    // never unmap buffers that were created in this process    private_handle_t* hnd = (private_handle_t*)handle;    if (hnd->pid != getpid()) {        if (hnd->base) {            gralloc_unmap(module, handle);        }    }    return 0;}int mapBuffer(gralloc_module_t const* module,        private_handle_t* hnd){    void* vaddr;    return gralloc_map(module, hnd, &vaddr);}int terminateBuffer(gralloc_module_t const* module,        private_handle_t* hnd){    if (hnd->base) {        // this buffer was mapped, unmap it now        gralloc_unmap(module, hnd);    }    return 0;}//图形缓冲区的锁定int gralloc_lock(gralloc_module_t const* module,        buffer_handle_t handle, int usage,        int l, int t, int w, int h,        void** vaddr){    // this is called when a buffer is being locked for software    // access. in thin implementation we have nothing to do since    // not synchronization with the h/w is needed.    // typically this is used to wait for the h/w to finish with    // this buffer if relevant. the data cache may need to be    // flushed or invalidated depending on the usage bits and the    // hardware.    if (private_handle_t::validate(handle) < 0)        return -EINVAL;//检测参数并返回帧缓冲区的基址，锁定操作并没有实现，需要调用者实现    private_handle_t* hnd = (private_handle_t*)handle;    *vaddr = (void*)hnd->base;    return 0;}//图形缓冲区的解锁定int gralloc_unlock(gralloc_module_t const* module,         buffer_handle_t handle){    // we're done with a software buffer. nothing to do in this    // implementation. typically this is used to flush the data cache.//解锁操作没实现，交给调用者实现    if (private_handle_t::validate(handle) < 0)        return -EINVAL;    return 0;}

总结

        经过详细的分析发现，分配图形缓冲区和映射过程是有重叠逻辑的，在分配的过程中就需要做映射操作；还有帧缓冲区初始化时，也会有映射操作。只不过Gralloc模块单独将映射过程封装出来了，即提供register_gralloc_buffer给调用者，用来映射图形缓冲区到进程的虚拟地址空间。

       总体上，Gralloc模块还是提供了这三种抽象功能：分配、映射、渲染。其中gralloc设备打开过程，为调用者返回了gralloc_alloc方法；fb设备打开过程，获取了帧缓冲区的信息、并初始化了虚拟显示屏，同时映射了帧缓冲区，并返回了渲染方法fb_post。而gralloc模块，提供了register_gralloc_buffer方法给调用者用来映射。

参考：http://www.myexception.cn/image/1442367.html