在Android系统中,对于硬件的操作,使用HAL Stub的方式来实现。HAL Stub的具体写法请参照Android中HAL如何向上层提供接口总结 。
在我们写完HAL Stub之后,这个HAL Stub是如何被应用获取,如何被应用程序调用的呢?
显然,由于HAL Stub本质上是一个.so,在调用之后,需要上层应用对其进行加载,然后才能调用。哪么,HAL Stub的加载器是如何实现对不同的Hardware HAL Stub进行通用性调用的呢? 按常规,每个Hareware HAL Stub应该有一个唯一的名字,且有一个通用的规则和一个入口函数。下面看看HAL Stub是如何实现这两个功能的。下面的描述以gralloc为例。
1. 唯一的id
- #define GRALLOC_HARDWARE_MODULE_ID "gralloc"
#define GRALLOC_HARDWARE_MODULE_ID "gralloc"
2. hw_module_t实例
每个硬件模块都有一个包含hw_module_t(为第一个成员)数据结构的实例,且实例的名字为:HAL_MODULE_INFO_SYM,它本身是一个宏定义,其定义如下:
hardware.h (通用的东东都在hardware.h和hardware.c中)
- /**
- * Name of the hal_module_info
- */
- #define HAL_MODULE_INFO_SYM HMI //.so中将一个符号HMI,获取此符号的地址,就获取到了对应的hw_module_t地址
- /**
- * Name of the hal_module_info as a string
- */
- #define HAL_MODULE_INFO_SYM_AS_STR "HMI"
/** * Name of the hal_module_info */ #define HAL_MODULE_INFO_SYM HMI //.so中将一个符号HMI,获取此符号的地址,就获取到了对应的hw_module_t地址 /** * Name of the hal_module_info as a string */ #define HAL_MODULE_INFO_SYM_AS_STR "HMI"
- /**
- * Every hardware module must have a data structure named HAL_MODULE_INFO_SYM
- * and the fields of this data structure must begin with hw_module_t
- * followed by module specific information.
- */
- typedef struct gralloc_module_t {
- struct hw_module_t common;
- int (*registerBuffer)(struct gralloc_module_t
const* module, - buffer_handle_t handle);
- int (*unregisterBuffer)(struct gralloc_module_t
const* module, - buffer_handle_t handle);
- int (*lock)(struct gralloc_module_t
const* module, - buffer_handle_t handle, int usage,
- int l, int t,
int w, int h,
- void** vaddr);
- int (*unlock)(struct gralloc_module_t
const* module, - buffer_handle_t handle);
- /* reserved for future use */
- int (*perform)(struct gralloc_module_t
const* module, - int operation, ... );
- /* reserved for future use */
- void* reserved_proc[7];
- }
/** * Every hardware module must have a data structure named HAL_MODULE_INFO_SYM * and the fields of this data structure must begin with hw_module_t * followed by module specific information. */ typedef struct gralloc_module_t { struct hw_module_t common; int (*registerBuffer)(struct gralloc_module_t const* module, buffer_handle_t handle); int (*unregisterBuffer)(struct gralloc_module_t const* module, buffer_handle_t handle); int (*lock)(struct gralloc_module_t const* module, buffer_handle_t handle, int usage, int l, int t, int w, int h, void** vaddr); int (*unlock)(struct gralloc_module_t const* module, buffer_handle_t handle); /* reserved for future use */ int (*perform)(struct gralloc_module_t const* module, int operation, ... ); /* reserved for future use */ void* reserved_proc[7]; }
- struct private_module_t {
- gralloc_module_t base;
- struct private_handle_t* framebuffer;
- uint32_t flags;
- uint32_t numBuffers;
- uint32_t bufferMask;
- pthread_mutex_t lock;
- buffer_handle_t currentBuffer;
- int pmem_master;
- void* pmem_master_base;
- unsigned long master_phys;
- int gpu;
- void* gpu_base;
- int fb_map_offset;
- struct fb_var_screeninfo info;
- struct fb_fix_screeninfo finfo;
- float xdpi;
- float ydpi;
- float fps;
- };
struct private_module_t { gralloc_module_t base; struct private_handle_t* framebuffer; uint32_t flags; uint32_t numBuffers; uint32_t bufferMask; pthread_mutex_t lock; buffer_handle_t currentBuffer; int pmem_master; void* pmem_master_base; unsigned long master_phys; int gpu; void* gpu_base; int fb_map_offset; struct fb_var_screeninfo info; struct fb_fix_screeninfo finfo; float xdpi; float ydpi; float fps; };
其实例为:
- static struct hw_module_methods_t gralloc_module_methods = {
- open: gralloc_device_open
- };
static struct hw_module_methods_t gralloc_module_methods = { open: gralloc_device_open };
- 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,
- };
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, };
3. 从HAL Stub(.so)中获取hw_module_t(即private_module_t)
调用函数int hw_get_module(const char *id, const struct hw_module_t **module),其中id为就是1中所讲的GRALLOC_HARDWARE_MODULE_ID,第二个参数为我们要获取的hw_module_t。
下面以在FramebufferNativeWindow::FramebufferNativeWindow中的调用流程为例(FramebufferNativeWindow实现FrameBuffer的管理,它主要被SurfaceFlinger使用,也可以被OpenGL Native程序使用。在本质上,它在Framebuffer之上实现了一个ANativeWindow,目前它只管理两个buffers:front and back buffer.)
- FramebufferNativeWindow::FramebufferNativeWindow()
- : BASE(), fbDev(0), grDev(0), mUpdateOnDemand(false)
- {
- hw_module_t const* module;
- if (hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module) == 0) {
- int stride;
- int err;
- int i;
- err = framebuffer_open(module, &fbDev);
- LOGE_IF(err, "couldn't open framebuffer HAL (%s)", strerror(-err));
- err = gralloc_open(module, &grDev);
- LOGE_IF(err, "couldn't open gralloc HAL (%s)", strerror(-err));
- // bail out if we can't initialize the modules
- if (!fbDev || !grDev)
- return;
- mUpdateOnDemand = (fbDev->setUpdateRect != 0);
- // initialize the buffer FIFO
- mNumBuffers = NUM_FRAME_BUFFERS;
- mNumFreeBuffers = NUM_FRAME_BUFFERS;
- mBufferHead = mNumBuffers-1;
- for (i = 0; i < mNumBuffers; i++)
- {
- buffers[i] = new NativeBuffer(
- fbDev->width, fbDev->height, fbDev->format, GRALLOC_USAGE_HW_FB);
- }
- for (i = 0; i < mNumBuffers; i++)
- {
- err = grDev->alloc(grDev,
- fbDev->width, fbDev->height, fbDev->format,
- GRALLOC_USAGE_HW_FB, &buffers[i]->handle, &buffers[i]->stride);
- LOGE_IF(err, "fb buffer %d allocation failed w=%d, h=%d, err=%s",
- i, fbDev->width, fbDev->height, strerror(-err));
- if (err)
- {
- mNumBuffers = i;
- mNumFreeBuffers = i;
- mBufferHead = mNumBuffers-1;
- break;
- }
- }
- const_cast<uint32_t&>(ANativeWindow::flags) = fbDev->flags;
- const_cast<float&>(ANativeWindow::xdpi) = fbDev->xdpi;
- const_cast<float&>(ANativeWindow::ydpi) = fbDev->ydpi;
- const_cast<int&>(ANativeWindow::minSwapInterval) =
- fbDev->minSwapInterval;
- const_cast<int&>(ANativeWindow::maxSwapInterval) =
- fbDev->maxSwapInterval;
- }
- else
- {
- LOGE("Couldn't get gralloc module");
- }
- ANativeWindow::setSwapInterval = setSwapInterval;
- ANativeWindow::dequeueBuffer = dequeueBuffer;
- ANativeWindow::lockBuffer = lockBuffer;
- ANativeWindow::queueBuffer = queueBuffer;
- ANativeWindow::query = query;
- ANativeWindow::perform = perform;
- }
FramebufferNativeWindow::FramebufferNativeWindow() : BASE(), fbDev(0), grDev(0), mUpdateOnDemand(false) { hw_module_t const* module; if (hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module) == 0) { int stride; int err; int i; err = framebuffer_open(module, &fbDev); LOGE_IF(err, "couldn't open framebuffer HAL (%s)", strerror(-err)); err = gralloc_open(module, &grDev); LOGE_IF(err, "couldn't open gralloc HAL (%s)", strerror(-err)); // bail out if we can't initialize the modules if (!fbDev || !grDev) return; mUpdateOnDemand = (fbDev->setUpdateRect != 0); // initialize the buffer FIFO mNumBuffers = NUM_FRAME_BUFFERS; mNumFreeBuffers = NUM_FRAME_BUFFERS; mBufferHead = mNumBuffers-1; for (i = 0; i < mNumBuffers; i++) { buffers[i] = new NativeBuffer( fbDev->width, fbDev->height, fbDev->format, GRALLOC_USAGE_HW_FB); } for (i = 0; i < mNumBuffers; i++) { err = grDev->alloc(grDev, fbDev->width, fbDev->height, fbDev->format, GRALLOC_USAGE_HW_FB, &buffers[i]->handle, &buffers[i]->stride); LOGE_IF(err, "fb buffer %d allocation failed w=%d, h=%d, err=%s", i, fbDev->width, fbDev->height, strerror(-err)); if (err) { mNumBuffers = i; mNumFreeBuffers = i; mBufferHead = mNumBuffers-1; break; } } const_cast<uint32_t&>(ANativeWindow::flags) = fbDev->flags; const_cast<float&>(ANativeWindow::xdpi) = fbDev->xdpi; const_cast<float&>(ANativeWindow::ydpi) = fbDev->ydpi; const_cast<int&>(ANativeWindow::minSwapInterval) = fbDev->minSwapInterval; const_cast<int&>(ANativeWindow::maxSwapInterval) = fbDev->maxSwapInterval; } else { LOGE("Couldn't get gralloc module"); } ANativeWindow::setSwapInterval = setSwapInterval; ANativeWindow::dequeueBuffer = dequeueBuffer; ANativeWindow::lockBuffer = lockBuffer; ANativeWindow::queueBuffer = queueBuffer; ANativeWindow::query = query; ANativeWindow::perform = perform; }
看看关键的hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module)都做了些什么?它在hardware.c中实现。相关代码如下:
- /** Base path of the hal modules */
- #define HAL_LIBRARY_PATH1 "/system/lib/hw"
- #define HAL_LIBRARY_PATH2 "/vendor/lib/hw"
- /**
- * There are a set of variant filename for modules. The form of the filename
- * is "<MODULE_ID>.variant.so" so for the led module the Dream variants
- * of base "ro.product.board", "ro.board.platform" and "ro.arch" would be:
- *
- * led.trout.so
- * led.msm7k.so
- * led.ARMV6.so
- * led.default.so
- */
- static const
char *variant_keys[] = { - "ro.hardware",
/* This goes first so that it can pick up a different - file on the emulator. */
- "ro.product.board",
- "ro.board.platform",
- "ro.arch"
- };
- static const
int HAL_VARIANT_KEYS_COUNT = - (sizeof(variant_keys)/sizeof(variant_keys[0]));
- /**
- * Load the file defined by the variant and if successful
- * return the dlopen handle and the hmi.
- * @return 0 = success, !0 = failure.
- */
- static int load(const
char *id, - const char *path,
- const struct hw_module_t **pHmi)
- {
- int status;
- void *handle;
- struct hw_module_t *hmi;
- /*
- * load the symbols resolving undefined symbols before
- * dlopen returns. Since RTLD_GLOBAL is not or'd in with
- * RTLD_NOW the external symbols will not be global
- */
- handle = dlopen(path, RTLD_NOW);
- if (handle == NULL) {
- char const *err_str = dlerror();
- LOGE("load: module=%s\n%s", path, err_str?err_str:"unknown");
- status = -EINVAL;
- goto done;
- }
- /* Get the address of the struct hal_module_info. */
- const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
- hmi = (struct hw_module_t *)dlsym(handle, sym);
- if (hmi == NULL) {
- LOGE("load: couldn't find symbol %s", sym);
- status = -EINVAL;
- goto done;
- }
- /* Check that the id matches */
- if (strcmp(id, hmi->id) != 0) {
- LOGE("load: id=%s != hmi->id=%s", id, hmi->id);
- status = -EINVAL;
- goto done;
- }
- hmi->dso = handle;
- /* success */
- status = 0;
- done:
- if (status != 0) {
- hmi = NULL;
- if (handle != NULL) {
- dlclose(handle);
- handle = NULL;
- }
- } else {
- LOGV("loaded HAL id=%s path=%s hmi=%p handle=%p",
- id, path, *pHmi, handle);
- }
- *pHmi = hmi;
- return status;
- }
- int hw_get_module_by_class(const
char *class_id, const
char *inst, - const struct hw_module_t **module)
- {
- int status;
- int i;
- const struct hw_module_t *hmi = NULL;
- char prop[PATH_MAX];
- char path[PATH_MAX];
- char name[PATH_MAX];
- if (inst)
- snprintf(name, PATH_MAX, "%s.%s", class_id, inst);
- else
- strlcpy(name, class_id, PATH_MAX);
- /*
- * Here we rely on the fact that calling dlopen multiple times on
- * the same .so will simply increment a refcount (and not load
- * a new copy of the library).
- * We also assume that dlopen() is thread-safe.
- */
- /* Loop through the configuration variants looking for a module */
- for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {
- if (i < HAL_VARIANT_KEYS_COUNT) {
- if (property_get(variant_keys[i], prop, NULL) == 0) {
- continue;
- }
- snprintf(path, sizeof(path),
"%s/%s.%s.so", - HAL_LIBRARY_PATH2, name, prop);
- if (access(path, R_OK) == 0)
break; - snprintf(path, sizeof(path),
"%s/%s.%s.so", - HAL_LIBRARY_PATH1, name, prop);
- if (access(path, R_OK) == 0)
break; - } else {
- snprintf(path, sizeof(path),
"%s/%s.default.so", - HAL_LIBRARY_PATH1, name);
- if (access(path, R_OK) == 0)
break; - }
- }
- status = -ENOENT;
- if (i < HAL_VARIANT_KEYS_COUNT+1) {
- /* load the module, if this fails, we're doomed, and we should not try
- * to load a different variant. */
- status = load(class_id, path, module);
- }
- return status;
- }
- int hw_get_module(const
char *id, const
struct hw_module_t **module) - {
- return hw_get_module_by_class(id, NULL, module);
- }
/** Base path of the hal modules */ #define HAL_LIBRARY_PATH1 "/system/lib/hw" #define HAL_LIBRARY_PATH2 "/vendor/lib/hw" /** * There are a set of variant filename for modules. The form of the filename * is "<MODULE_ID>.variant.so" so for the led module the Dream variants * of base "ro.product.board", "ro.board.platform" and "ro.arch" would be: * * led.trout.so * led.msm7k.so * led.ARMV6.so * led.default.so */ static const char *variant_keys[] = { "ro.hardware", /* This goes first so that it can pick up a different file on the emulator. */ "ro.product.board", "ro.board.platform", "ro.arch" }; static const int HAL_VARIANT_KEYS_COUNT = (sizeof(variant_keys)/sizeof(variant_keys[0])); /** * Load the file defined by the variant and if successful * return the dlopen handle and the hmi. * @return 0 = success, !0 = failure. */ static int load(const char *id, const char *path, const struct hw_module_t **pHmi) { int status; void *handle; struct hw_module_t *hmi; /* * load the symbols resolving undefined symbols before * dlopen returns. Since RTLD_GLOBAL is not or'd in with * RTLD_NOW the external symbols will not be global */ handle = dlopen(path, RTLD_NOW); if (handle == NULL) { char const *err_str = dlerror(); LOGE("load: module=%s\n%s", path, err_str?err_str:"unknown"); status = -EINVAL; goto done; } /* Get the address of the struct hal_module_info. */ const char *sym = HAL_MODULE_INFO_SYM_AS_STR; hmi = (struct hw_module_t *)dlsym(handle, sym); if (hmi == NULL) { LOGE("load: couldn't find symbol %s", sym); status = -EINVAL; goto done; } /* Check that the id matches */ if (strcmp(id, hmi->id) != 0) { LOGE("load: id=%s != hmi->id=%s", id, hmi->id); status = -EINVAL; goto done; } hmi->dso = handle; /* success */ status = 0; done: if (status != 0) { hmi = NULL; if (handle != NULL) { dlclose(handle); handle = NULL; } } else { LOGV("loaded HAL id=%s path=%s hmi=%p handle=%p", id, path, *pHmi, handle); } *pHmi = hmi; return status; } int hw_get_module_by_class(const char *class_id, const char *inst, const struct hw_module_t **module) { int status; int i; const struct hw_module_t *hmi = NULL; char prop[PATH_MAX]; char path[PATH_MAX]; char name[PATH_MAX]; if (inst) snprintf(name, PATH_MAX, "%s.%s", class_id, inst); else strlcpy(name, class_id, PATH_MAX); /* * Here we rely on the fact that calling dlopen multiple times on * the same .so will simply increment a refcount (and not load * a new copy of the library). * We also assume that dlopen() is thread-safe. */ /* Loop through the configuration variants looking for a module */ for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) { if (i < HAL_VARIANT_KEYS_COUNT) { if (property_get(variant_keys[i], prop, NULL) == 0) { continue; } snprintf(path, sizeof(path), "%s/%s.%s.so", HAL_LIBRARY_PATH2, name, prop); if (access(path, R_OK) == 0) break; snprintf(path, sizeof(path), "%s/%s.%s.so", HAL_LIBRARY_PATH1, name, prop); if (access(path, R_OK) == 0) break; } else { snprintf(path, sizeof(path), "%s/%s.default.so", HAL_LIBRARY_PATH1, name); if (access(path, R_OK) == 0) break; } } status = -ENOENT; if (i < HAL_VARIANT_KEYS_COUNT+1) { /* load the module, if this fails, we're doomed, and we should not try * to load a different variant. */ status = load(class_id, path, module); } return status; } int hw_get_module(const char *id, const struct hw_module_t **module) { return hw_get_module_by_class(id, NULL, module); }
其关键在于load函数中的下面两行代码:
- const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
- hmi = (struct hw_module_t *)dlsym(handle, sym);
const char *sym = HAL_MODULE_INFO_SYM_AS_STR; hmi = (struct hw_module_t *)dlsym(handle, sym);
在打开的.so中查找HMI符号的地址,并保存在hmi中。至此,.so中的hw_module_t已经被成功获取,从而可以根据它获取别的相关接口。
4. 使用实例
代码如下:
- GraphicBufferAllocator::GraphicBufferAllocator()
- : mAllocDev(0)
- {
- hw_module_t const* module;
- int err = hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module);
- LOGE_IF(err, "FATAL: can't find the %s module", GRALLOC_HARDWARE_MODULE_ID);
- if (err == 0) {
- gralloc_open(module, &mAllocDev);
- }
- }
GraphicBufferAllocator::GraphicBufferAllocator() : mAllocDev(0) { hw_module_t const* module; int err = hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module); LOGE_IF(err, "FATAL: can't find the %s module", GRALLOC_HARDWARE_MODULE_ID); if (err == 0) { gralloc_open(module, &mAllocDev); } }
5. 总结
1)HAL通过hw_get_module函数获取hw_module_t
2)HAL通过hw_module_t->methods->open获取hw_device_t指针,并在此open函数中初始化hw_device_t的包装结构中的函数及hw_device_t中的close函数,如gralloc_device_open。
3)三个重要的数据结构:
a) struct hw_device_t: 表示硬件设备,存储了各种硬件设备的公共属性和方法
b)struct hw_module_t: 可用hw_get_module进行加载的module
c)struct hw_module_methods_t: 用于定义操作设备的方法,其中只定义了一个打开设备的方法open.
- typedef struct hw_module_t {
- /** tag must be initialized to HARDWARE_MODULE_TAG */
- uint32_t tag;
- /** major version number for the module */
- uint16_t version_major;
- /** minor version number of the module */
- uint16_t version_minor;
- /** Identifier of module */
- const char *id;
- /** Name of this module */
- const char *name;
- /** Author/owner/implementor of the module */
- const char *author;
- /** Modules methods */
- struct hw_module_methods_t* methods;
- /** module's dso */
- void* dso;
- /** padding to 128 bytes, reserved for future use */
- uint32_t reserved[32-7];
- } hw_module_t;
- typedef struct hw_module_methods_t {
- /** Open a specific device */
- int (*open)(const
struct hw_module_t* module, const
char* id, - struct hw_device_t** device);
- } hw_module_methods_t;
- /**
- * Every device data structure must begin with hw_device_t
- * followed by module specific public methods and attributes.
- */
- typedef struct hw_device_t {
- /** tag must be initialized to HARDWARE_DEVICE_TAG */
- uint32_t tag;
- /** version number for hw_device_t */
- uint32_t version;
- /** reference to the module this device belongs to */
- struct hw_module_t* module;
- /** padding reserved for future use */
- uint32_t reserved[12];
- /** Close this device */
- int (*close)(struct hw_device_t* device);
- } hw_device_t;
typedef struct hw_module_t { /** tag must be initialized to HARDWARE_MODULE_TAG */ uint32_t tag; /** major version number for the module */ uint16_t version_major; /** minor version number of the module */ uint16_t version_minor; /** Identifier of module */ const char *id; /** Name of this module */ const char *name; /** Author/owner/implementor of the module */ const char *author; /** Modules methods */ struct hw_module_methods_t* methods; /** module's dso */ void* dso; /** padding to 128 bytes, reserved for future use */ uint32_t reserved[32-7]; } hw_module_t; typedef struct hw_module_methods_t { /** Open a specific device */ int (*open)(const struct hw_module_t* module, const char* id, struct hw_device_t** device); } hw_module_methods_t; /** * Every device data structure must begin with hw_device_t * followed by module specific public methods and attributes. */ typedef struct hw_device_t { /** tag must be initialized to HARDWARE_DEVICE_TAG */ uint32_t tag; /** version number for hw_device_t */ uint32_t version; /** reference to the module this device belongs to */ struct hw_module_t* module; /** padding reserved for future use */ uint32_t reserved[12]; /** Close this device */ int (*close)(struct hw_device_t* device); } hw_device_t;
hw_device_t通过open方法获取。