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Android HAL的被调用流程

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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

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  1. #define GRALLOC_HARDWARE_MODULE_ID “gralloc”

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  1. #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)

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  1. /*
  2. Name of the hal_module_info
  3. */
  4. #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
  6. /*
  7. Name of the hal_module_info as a string
  8. */
  9. #define HAL_MODULE_INFO_SYM_AS_STR “HMI”

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  1. /** 
  2.  * Name of the hal_module_info 
  3.  */  
  4. #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  
  5.   
  6. /** 
  7.  * Name of the hal_module_info as a string 
  8.  */  
  9. #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"

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  1. /*
  2. Every hardware module must have a data structure named HAL_MODULE_INFO_SYM
  3. * and the fields of this data structure must begin with hw_module_t
  4. * followed by module specific information.
  5. */
  6. typedef struct gralloc_module_t {
  7. struct hw_module_t common;
  9. int (*registerBuffer)(struct gralloc_module_t
    const* module,
  10. buffer_handle_t handle);
  12. int (*unregisterBuffer)(struct gralloc_module_t
    const* module,
  13. buffer_handle_t handle);
  15. int (*lock)(struct gralloc_module_t
    const* module,
  16. buffer_handle_t handle, int usage,
  17. int l, int t,
    int w, int h,
  18. void** vaddr);
  20. int (*unlock)(struct gralloc_module_t
    const* module,
  21. buffer_handle_t handle);
  23. /* reserved for future use */
  24. int (*perform)(struct gralloc_module_t
    const* module,
  25. int operation, … );
  26. /* reserved for future use */
  27. void* reserved_proc[7];
  28. }

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  1. /** 
  2.  * Every hardware module must have a data structure named HAL_MODULE_INFO_SYM 
  3.  * and the fields of this data structure must begin with hw_module_t 
  4.  * followed by module specific information. 
  5.  */  
  6. typedef struct gralloc_module_t {  
  7.     struct hw_module_t common;  
  8.       
  9.     int (*registerBuffer)(struct gralloc_module_t const* module,  
  10.             buffer_handle_t handle);  
  11.   
  12.     int (*unregisterBuffer)(struct gralloc_module_t const* module,  
  13.             buffer_handle_t handle);  
  14.       
  15.     int (*lock)(struct gralloc_module_t const* module,  
  16.             buffer_handle_t handle, int usage,  
  17.             int l, int t, int w, int h,  
  18.             void** vaddr);  
  19.       
  20.     int (*unlock)(struct gralloc_module_t const* module,  
  21.             buffer_handle_t handle);  
  22.   
  23.     /* reserved for future use */  
  24.     int (*perform)(struct gralloc_module_t const* module,  
  25.             int operation, … );  
  26.     /* reserved for future use */  
  27.     void* reserved_proc[7];  
  28. }  
/** * 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];}
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  1. struct private_module_t {
  2. gralloc_module_t base;
  4. struct private_handle_t* framebuffer;
  5. uint32_t flags;
  6. uint32_t numBuffers;
  7. uint32_t bufferMask;
  8. pthread_mutex_t lock;
  9. buffer_handle_t currentBuffer;
  10. int pmem_master;
  11. void* pmem_master_base;
  12. unsigned long master_phys;
  13. int gpu;
  14. void* gpu_base;
  15. int fb_map_offset;
  17. struct fb_var_screeninfo info;
  18. struct fb_fix_screeninfo finfo;
  19. float xdpi;
  20. float ydpi;
  21. float fps;
  22. };

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  1. struct private_module_t {  
  2.     gralloc_module_t base;  
  3.   
  4.     struct private_handle_t* framebuffer;  
  5.     uint32_t flags;  
  6.     uint32_t numBuffers;  
  7.     uint32_t bufferMask;  
  8.     pthread_mutex_t lock;  
  9.     buffer_handle_t currentBuffer;  
  10.     int pmem_master;  
  11.     void* pmem_master_base;  
  12.     unsigned long master_phys;  
  13.     int gpu;  
  14.     void* gpu_base;  
  15.     int fb_map_offset;  
  16.   
  17.     struct fb_var_screeninfo info;  
  18.     struct fb_fix_screeninfo finfo;  
  19.     float xdpi;  
  20.     float ydpi;  
  21.     float fps;  
  22. };  
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：

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  1. static struct hw_module_methods_t gralloc_module_methods = {
  2. open: gralloc_device_open
  3. };

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  1. static struct hw_module_methods_t gralloc_module_methods = {  
  2.         open: gralloc_device_open  
  3. };  
static struct hw_module_methods_t gralloc_module_methods = {        open: gralloc_device_open};

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  1. struct private_module_t HAL_MODULE_INFO_SYM = {
  2. base: {
  3. common: {
  4. tag: HARDWARE_MODULE_TAG,
  5. version_major: 1,
  6. version_minor: 0,
  7. id: GRALLOC_HARDWARE_MODULE_ID,
  8. name: “Graphics Memory Allocator Module”,
  9. author: “The Android Open Source Project”,
  10. methods: &gralloc_module_methods
  11. },
  12. registerBuffer: gralloc_register_buffer,
  13. unregisterBuffer: gralloc_unregister_buffer,
  14. lock: gralloc_lock,
  15. unlock: gralloc_unlock,
  16. },
  17. framebuffer: 0,
  18. flags: 0,
  19. numBuffers: 0,
  20. bufferMask: 0,
  21. lock: PTHREAD_MUTEX_INITIALIZER,
  22. currentBuffer: 0,
  23. };

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  1. struct private_module_t HAL_MODULE_INFO_SYM = {  
  2.     base: {  
  3.         common: {  
  4.             tag: HARDWARE_MODULE_TAG,  
  5.             version_major: 1,  
  6.             version_minor: 0,  
  7.             id: GRALLOC_HARDWARE_MODULE_ID,  
  8.             name: ”Graphics Memory Allocator Module”,  
  9.             author: ”The Android Open Source Project”,  
  10.             methods: &gralloc_module_methods  
  11.         },  
  12.         registerBuffer: gralloc_register_buffer,  
  13.         unregisterBuffer: gralloc_unregister_buffer,  
  14.         lock: gralloc_lock,  
  15.         unlock: gralloc_unlock,  
  16.     },  
  17.     framebuffer: 0,  
  18.     flags: 0,  
  19.     numBuffers: 0,  
  20.     bufferMask: 0,  
  21.     lock: PTHREAD_MUTEX_INITIALIZER,  
  22.     currentBuffer: 0,  
  23. };  
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.）

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  1. FramebufferNativeWindow::FramebufferNativeWindow()
  2. : BASE(), fbDev(0), grDev(0), mUpdateOnDemand(false)
  3. {
  4. hw_module_t const* module;
  5. if (hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module) == 0) {
  6. int stride;
  7. int err;
  8. int i;
  9. err = framebuffer_open(module, &fbDev);
  10. LOGE_IF(err, “couldn’t open framebuffer HAL (%s)”, strerror(-err));
  12. err = gralloc_open(module, &grDev);
  13. LOGE_IF(err, “couldn’t open gralloc HAL (%s)”, strerror(-err));
  15. // bail out if we can’t initialize the modules
  16. if (!fbDev || !grDev)
  17. return;
  19. mUpdateOnDemand = (fbDev->setUpdateRect != 0);
  21. // initialize the buffer FIFO
  22. mNumBuffers = NUM_FRAME_BUFFERS;
  23. mNumFreeBuffers = NUM_FRAME_BUFFERS;
  24. mBufferHead = mNumBuffers-1;
  26. for (i = 0; i < mNumBuffers; i++)
  27. {
  28. buffers[i] = new NativeBuffer(
  29. fbDev->width, fbDev->height, fbDev->format, GRALLOC_USAGE_HW_FB);
  30. }
  32. for (i = 0; i < mNumBuffers; i++)
  33. {
  34. err = grDev->alloc(grDev,
  35. fbDev->width, fbDev->height, fbDev->format,
  36. GRALLOC_USAGE_HW_FB, &buffers[i]->handle, &buffers[i]->stride);
  38. LOGE_IF(err, “fb buffer %d allocation failed w=%d, h=%d, err=%s”,
  39. i, fbDev->width, fbDev->height, strerror(-err));
  41. if (err)
  42. {
  43. mNumBuffers = i;
  44. mNumFreeBuffers = i;
  45. mBufferHead = mNumBuffers-1;
  46. break;
  47. }
  48. }
  50. const_cast<uint32_t&>(ANativeWindow::flags) = fbDev->flags;
  51. const_cast<float&>(ANativeWindow::xdpi) = fbDev->xdpi;
  52. const_cast<float&>(ANativeWindow::ydpi) = fbDev->ydpi;
  53. const_cast<int&>(ANativeWindow::minSwapInterval) =
  54. fbDev->minSwapInterval;
  55. const_cast<int&>(ANativeWindow::maxSwapInterval) =
  56. fbDev->maxSwapInterval;
  57. }
  58. else
  59. {
  60. LOGE(“Couldn’t get gralloc module”);
  61. }
  63. ANativeWindow::setSwapInterval = setSwapInterval;
  64. ANativeWindow::dequeueBuffer = dequeueBuffer;
  65. ANativeWindow::lockBuffer = lockBuffer;
  66. ANativeWindow::queueBuffer = queueBuffer;
  67. ANativeWindow::query = query;
  68. ANativeWindow::perform = perform;
  69. }

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  1. FramebufferNativeWindow::FramebufferNativeWindow()   
  2.     : BASE(), fbDev(0), grDev(0), mUpdateOnDemand(false)  
  3. {  
  4.     hw_module_t const* module;  
  5.     if (hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module) == 0) {  
  6.         int stride;  
  7.         int err;  
  8.         int i;  
  9.         err = framebuffer_open(module, &fbDev);  
  10.         LOGE_IF(err, ”couldn’t open framebuffer HAL (%s)”, strerror(-err));  
  11.           
  12.         err = gralloc_open(module, &grDev);  
  13.         LOGE_IF(err, ”couldn’t open gralloc HAL (%s)”, strerror(-err));  
  14.   
  15.         // bail out if we can’t initialize the modules  
  16.         if (!fbDev || !grDev)  
  17.             return;  
  18.           
  19.         mUpdateOnDemand = (fbDev->setUpdateRect != 0);  
  20.           
  21.         // initialize the buffer FIFO  
  22.         mNumBuffers = NUM_FRAME_BUFFERS;  
  23.         mNumFreeBuffers = NUM_FRAME_BUFFERS;  
  24.         mBufferHead = mNumBuffers-1;  
  25.   
  26.         for (i = 0; i < mNumBuffers; i++)  
  27.         {  
  28.                 buffers[i] = new NativeBuffer(  
  29.                         fbDev->width, fbDev->height, fbDev->format, GRALLOC_USAGE_HW_FB);  
  30.         }  
  31.   
  32.         for (i = 0; i < mNumBuffers; i++)  
  33.         {  
  34.                 err = grDev->alloc(grDev,  
  35.                         fbDev->width, fbDev->height, fbDev->format,  
  36.                         GRALLOC_USAGE_HW_FB, &buffers[i]->handle, &buffers[i]->stride);  
  37.   
  38.                 LOGE_IF(err, ”fb buffer %d allocation failed w=%d, h=%d, err=%s”,  
  39.                         i, fbDev->width, fbDev->height, strerror(-err));  
  40.   
  41.                 if (err)  
  42.                 {  
  43.                         mNumBuffers = i;  
  44.                         mNumFreeBuffers = i;  
  45.                         mBufferHead = mNumBuffers-1;  
  46.                         break;  
  47.                 }  
  48.         }  
  49.   
  50.         const_cast<uint32_t&>(ANativeWindow::flags) = fbDev->flags;   
  51.         const_cast<float&>(ANativeWindow::xdpi) = fbDev->xdpi;  
  52.         const_cast<float&>(ANativeWindow::ydpi) = fbDev->ydpi;  
  53.         const_cast<int&>(ANativeWindow::minSwapInterval) =   
  54.             fbDev->minSwapInterval;  
  55.         const_cast<int&>(ANativeWindow::maxSwapInterval) =   
  56.             fbDev->maxSwapInterval;  
  57.     }   
  58.     else   
  59.     {  
  60.          LOGE(”Couldn’t get gralloc module”);  
  61.     }  
  62.   
  63.     ANativeWindow::setSwapInterval = setSwapInterval;  
  64.     ANativeWindow::dequeueBuffer = dequeueBuffer;  
  65.     ANativeWindow::lockBuffer = lockBuffer;  
  66.     ANativeWindow::queueBuffer = queueBuffer;  
  67.     ANativeWindow::query = query;  
  68.     ANativeWindow::perform = perform;  
  69. }  
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：

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  1. /* Base path of the hal modules /
  2. #define HAL_LIBRARY_PATH1 “/system/lib/hw”
  3. #define HAL_LIBRARY_PATH2 “/vendor/lib/hw”
  5. /*
  6. There are a set of variant filename for modules. The form of the filename
  7. * is “<MODULE_ID>.variant.so” so for the led module the Dream variants
  8. * of base “ro.product.board”, “ro.board.platform” and “ro.arch” would be:
  10. led.trout.so
  11. * led.msm7k.so
  12. * led.ARMV6.so
  13. * led.default.so
  14. */
  16. static const
    char *variant_keys[] = {
  17. “ro.hardware”,
    /* This goes first so that it can pick up a different
  18. file on the emulator. */
  19. “ro.product.board”,
  20. “ro.board.platform”,
  21. “ro.arch”
  22. };
  24. static const
    int HAL_VARIANT_KEYS_COUNT =
  25. (sizeof(variant_keys)/sizeof(variant_keys[0]));
  27. /*
  28. Load the file defined by the variant and if successful
  29. * return the dlopen handle and the hmi.
  30. * @return 0 = success, !0 = failure.
  31. */
  32. static int load(const
    char *id,
  33. const char *path,
  34. const struct hw_module_t **pHmi)
  35. {
  36. int status;
  37. void *handle;
  38. struct hw_module_t *hmi;
  40. /
  41. load the symbols resolving undefined symbols before
  42. * dlopen returns. Since RTLD_GLOBAL is not or’d in with
  43. * RTLD_NOW the external symbols will not be global
  44. */
  45. handle = dlopen(path, RTLD_NOW);
  46. if (handle == NULL) {
  47. char const *err_str = dlerror();
  48. LOGE(“load: module=%s\n%s”, path, err_str?err_str:“unknown”);
  49. status = -EINVAL;
  50. goto done;
  51. }
  53. /* Get the address of the struct hal_module_info. */
  54. const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
  55. hmi = (struct hw_module_t *)dlsym(handle, sym);
  56. if (hmi == NULL) {
  57. LOGE(“load: couldn’t find symbol %s”, sym);
  58. status = -EINVAL;
  59. goto done;
  60. }
  62. /* Check that the id matches */
  63. if (strcmp(id, hmi->id) != 0) {
  64. LOGE(“load: id=%s != hmi->id=%s”, id, hmi->id);
  65. status = -EINVAL;
  66. goto done;
  67. }
  69. hmi->dso = handle;
  71. /* success */
  72. status = 0;
  74. done:
  75. if (status != 0) {
  76. hmi = NULL;
  77. if (handle != NULL) {
  78. dlclose(handle);
  79. handle = NULL;
  80. }
  81. } else {
  82. LOGV(“loaded HAL id=%s path=%s hmi=%p handle=%p”,
  83. id, path, *pHmi, handle);
  84. }
  86. *pHmi = hmi;
  88. return status;
  89. }
  91. int hw_get_module_by_class(const
    char *class_id, const
    char *inst,
  92. const struct hw_module_t **module)
  93. {
  94. int status;
  95. int i;
  96. const struct hw_module_t *hmi = NULL;
  97. char prop[PATH_MAX];
  98. char path[PATH_MAX];
  99. char name[PATH_MAX];
  101. if (inst)
  102. snprintf(name, PATH_MAX, “%s.%s”, class_id, inst);
  103. else
  104. strlcpy(name, class_id, PATH_MAX);
  106. /
  107. Here we rely on the fact that calling dlopen multiple times on
  108. * the same .so will simply increment a refcount (and not load
  109. * a new copy of the library).
  110. * We also assume that dlopen() is thread-safe.
  111. /
  113. / Loop through the configuration variants looking for a module */
  114. for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {
  115. if (i < HAL_VARIANT_KEYS_COUNT) {
  116. if (property_get(variant_keys[i], prop, NULL) == 0) {
  117. continue;
  118. }
  119. snprintf(path, sizeof(path),
    “%s/%s.%s.so”,
  120. HAL_LIBRARY_PATH2, name, prop);
  121. if (access(path, R_OK) == 0)
    break;
  123. snprintf(path, sizeof(path),
    “%s/%s.%s.so”,
  124. HAL_LIBRARY_PATH1, name, prop);
  125. if (access(path, R_OK) == 0)
    break;
  126. } else {
  127. snprintf(path, sizeof(path),
    “%s/%s.default.so”,
  128. HAL_LIBRARY_PATH1, name);
  129. if (access(path, R_OK) == 0)
    break;
  130. }
  131. }
  133. status = -ENOENT;
  134. if (i < HAL_VARIANT_KEYS_COUNT+1) {
  135. /* load the module, if this fails, we’re doomed, and we should not try
  136. * to load a different variant. */
  137. status = load(class_id, path, module);
  138. }
  140. return status;
  141. }
  143. int hw_get_module(const
    char *id, const
    struct hw_module_t **module)
  144. {
  145. return hw_get_module_by_class(id, NULL, module);
  146. }

[cpp] view plain copy
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  1. /** Base path of the hal modules */  
  2. #define HAL_LIBRARY_PATH1 ”/system/lib/hw”  
  3. #define HAL_LIBRARY_PATH2 ”/vendor/lib/hw”  
  4.   
  5. /** 
  6.  * There are a set of variant filename for modules. The form of the filename 
  7.  * is ”<MODULE_ID>.variant.so” so for the led module the Dream variants  
  8.  * of base “ro.product.board”, “ro.board.platform” and “ro.arch” would be: 
  9.  * 
  10.  * led.trout.so 
  11.  * led.msm7k.so 
  12.  * led.ARMV6.so 
  13.  * led.default.so 
  14.  */  
  15.   
  16. static const char *variant_keys[] = {  
  17.     ”ro.hardware”,  /* This goes first so that it can pick up a different 
  18.                        file on the emulator. */  
  19.     ”ro.product.board”,  
  20.     ”ro.board.platform”,  
  21.     ”ro.arch”  
  22. };  
  23.   
  24. static const int HAL_VARIANT_KEYS_COUNT =  
  25.     (sizeof(variant_keys)/sizeof(variant_keys[0]));  
  26.   
  27. /** 
  28.  * Load the file defined by the variant and if successful 
  29.  * return the dlopen handle and the hmi. 
  30.  * @return 0 = success, !0 = failure. 
  31.  */  
  32. static int load(const char *id,  
  33.         const char *path,  
  34.         const struct hw_module_t **pHmi)  
  35. {  
  36.     int status;  
  37.     void *handle;  
  38.     struct hw_module_t *hmi;  
  39.   
  40.     /* 
  41.      * load the symbols resolving undefined symbols before 
  42.      * dlopen returns. Since RTLD_GLOBAL is not or’d in with 
  43.      * RTLD_NOW the external symbols will not be global 
  44.      */  
  45.     handle = dlopen(path, RTLD_NOW);  
  46.     if (handle == NULL) {  
  47.         char const *err_str = dlerror();  
  48.         LOGE(”load: module=%s\n%s”, path, err_str?err_str:“unknown”);  
  49.         status = -EINVAL;  
  50.         goto done;  
  51.     }  
  52.   
  53.     /* Get the address of the struct hal_module_info. */  
  54.     const char *sym = HAL_MODULE_INFO_SYM_AS_STR;  
  55.     hmi = (struct hw_module_t *)dlsym(handle, sym);  
  56.     if (hmi == NULL) {  
  57.         LOGE(”load: couldn’t find symbol %s”, sym);  
  58.         status = -EINVAL;  
  59.         goto done;  
  60.     }  
  61.   
  62.     /* Check that the id matches */  
  63.     if (strcmp(id, hmi->id) != 0) {  
  64.         LOGE(”load: id=%s != hmi->id=%s”, id, hmi->id);  
  65.         status = -EINVAL;  
  66.         goto done;  
  67.     }  
  68.   
  69.     hmi->dso = handle;  
  70.   
  71.     /* success */  
  72.     status = 0;  
  73.   
  74.     done:  
  75.     if (status != 0) {  
  76.         hmi = NULL;  
  77.         if (handle != NULL) {  
  78.             dlclose(handle);  
  79.             handle = NULL;  
  80.         }  
  81.     } else {  
  82.         LOGV(”loaded HAL id=%s path=%s hmi=%p handle=%p”,  
  83.                 id, path, *pHmi, handle);  
  84.     }  
  85.   
  86.     *pHmi = hmi;  
  87.   
  88.     return status;  
  89. }  
  90.   
  91. int hw_get_module_by_class(const char *class_id, const char *inst,  
  92.                            const struct hw_module_t **module)  
  93. {  
  94.     int status;  
  95.     int i;  
  96.     const struct hw_module_t *hmi = NULL;  
  97.     char prop[PATH_MAX];  
  98.     char path[PATH_MAX];  
  99.     char name[PATH_MAX];  
  100.   
  101.     if (inst)  
  102.         snprintf(name, PATH_MAX, ”%s.%s”, class_id, inst);  
  103.     else  
  104.         strlcpy(name, class_id, PATH_MAX);  
  105.   
  106.     /* 
  107.      * Here we rely on the fact that calling dlopen multiple times on 
  108.      * the same .so will simply increment a refcount (and not load 
  109.      * a new copy of the library). 
  110.      * We also assume that dlopen() is thread-safe. 
  111.      */  
  112.   
  113.     /* Loop through the configuration variants looking for a module */  
  114.     for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {  
  115.         if (i < HAL_VARIANT_KEYS_COUNT) {  
  116.             if (property_get(variant_keys[i], prop, NULL) == 0) {  
  117.                 continue;  
  118.             }  
  119.             snprintf(path, sizeof(path), “%s/%s.%s.so”,  
  120.                      HAL_LIBRARY_PATH2, name, prop);  
  121.             if (access(path, R_OK) == 0) break;  
  122.   
  123.             snprintf(path, sizeof(path), “%s/%s.%s.so”,  
  124.                      HAL_LIBRARY_PATH1, name, prop);  
  125.             if (access(path, R_OK) == 0) break;  
  126.         } else {  
  127.             snprintf(path, sizeof(path), “%s/%s.default.so”,  
  128.                      HAL_LIBRARY_PATH1, name);  
  129.             if (access(path, R_OK) == 0) break;  
  130.         }  
  131.     }  
  132.   
  133.     status = -ENOENT;  
  134.     if (i < HAL_VARIANT_KEYS_COUNT+1) {  
  135.         /* load the module, if this fails, we’re doomed, and we should not try 
  136.          * to load a different variant. */  
  137.         status = load(class_id, path, module);  
  138.     }  
  139.   
  140.     return status;  
  141. }  
  142.   
  143. int hw_get_module(const char *id, const struct hw_module_t **module)  
  144. {  
  145.     return hw_get_module_by_class(id, NULL, module);  
  146. }  
/** 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：

[cpp] view plaincopyprint?

  1. const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
  2. hmi = (struct hw_module_t *)dlsym(handle, sym);

[cpp] view plain copy
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  1. const char *sym = HAL_MODULE_INFO_SYM_AS_STR;  
  2. 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：

[cpp] view plaincopyprint?

  1. GraphicBufferAllocator::GraphicBufferAllocator()
  2. : mAllocDev(0)
  3. {
  4. hw_module_t const* module;
  5. int err = hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module);
  6. LOGE_IF(err, “FATAL: can’t find the %s module”, GRALLOC_HARDWARE_MODULE_ID);
  7. if (err == 0) {
  8. gralloc_open(module, &mAllocDev);
  9. }
  10. }

[cpp] view plain copy
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  1. GraphicBufferAllocator::GraphicBufferAllocator()  
  2.     : mAllocDev(0)  
  3. {  
  4.     hw_module_t const* module;  
  5.     int err = hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module);  
  6.     LOGE_IF(err, ”FATAL: can’t find the %s module”, GRALLOC_HARDWARE_MODULE_ID);  
  7.     if (err == 0) {  
  8.         gralloc_open(module, &mAllocDev);  
  9.     }  
  10. }  
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.

[cpp] view plaincopyprint?

  1. typedef struct hw_module_t {
  2. /* tag must be initialized to HARDWARE_MODULE_TAG /
  3. uint32_t tag;
  5. /* major version number for the module /
  6. uint16_t version_major;
  8. /* minor version number of the module /
  9. uint16_t version_minor;
  11. /* Identifier of module /
  12. const char *id;
  14. /* Name of this module /
  15. const char *name;
  17. /* Author/owner/implementor of the module /
  18. const char *author;
  20. /* Modules methods /
  21. struct hw_module_methods_t* methods;
  23. /* module’s dso /
  24. void* dso;
  26. /* padding to 128 bytes, reserved for future use /
  27. uint32_t reserved[32-7];
  29. } hw_module_t;
  31. typedef struct hw_module_methods_t {
  32. /* Open a specific device /
  33. int (*open)(const
    struct hw_module_t* module, const
    char* id,
  34. struct hw_device_t** device);
  36. } hw_module_methods_t;
  38. /*
  39. Every device data structure must begin with hw_device_t
  40. * followed by module specific public methods and attributes.
  41. */
  42. typedef struct hw_device_t {
  43. /* tag must be initialized to HARDWARE_DEVICE_TAG /
  44. uint32_t tag;
  46. /* version number for hw_device_t /
  47. uint32_t version;
  49. /* reference to the module this device belongs to /
  50. struct hw_module_t* module;
  52. /* padding reserved for future use /
  53. uint32_t reserved[12];
  55. /* Close this device /
  56. int (close)(struct hw_device_t device);
  58. } hw_device_t;

[cpp] view plain copy
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  1. typedef struct hw_module_t {  
  2.     /** tag must be initialized to HARDWARE_MODULE_TAG */  
  3.     uint32_t tag;  
  4.   
  5.     /** major version number for the module */  
  6.     uint16_t version_major;  
  7.   
  8.     /** minor version number of the module */  
  9.     uint16_t version_minor;  
  10.   
  11.     /** Identifier of module */  
  12.     const char *id;  
  13.   
  14.     /** Name of this module */  
  15.     const char *name;  
  16.   
  17.     /** Author/owner/implementor of the module */  
  18.     const char *author;  
  19.   
  20.     /** Modules methods */  
  21.     struct hw_module_methods_t* methods;  
  22.   
  23.     /** module’s dso */  
  24.     void* dso;  
  25.   
  26.     /** padding to 128 bytes, reserved for future use */  
  27.     uint32_t reserved[32-7];  
  28.   
  29. } hw_module_t;  
  30.   
  31. typedef struct hw_module_methods_t {  
  32.     /** Open a specific device */  
  33.     int (*open)(const struct hw_module_t* module, const char* id,  
  34.             struct hw_device_t** device);  
  35.   
  36. } hw_module_methods_t;  
  37.   
  38. /** 
  39.  * Every device data structure must begin with hw_device_t 
  40.  * followed by module specific public methods and attributes. 
  41.  */  
  42. typedef struct hw_device_t {  
  43.     /** tag must be initialized to HARDWARE_DEVICE_TAG */  
  44.     uint32_t tag;  
  45.   
  46.     /** version number for hw_device_t */  
  47.     uint32_t version;  
  48.   
  49.     /** reference to the module this device belongs to */  
  50.     struct hw_module_t* module;  
  51.   
  52.     /** padding reserved for future use */  
  53.     uint32_t reserved[12];  
  54.   
  55.     /** Close this device */  
  56.     int (*close)(struct hw_device_t* device);  
  57.   
  58. } 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。

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