hw_get_module详解

hw_get_module是jni层获取HAL层module的接口函数,原型为:int hw_get_module(const char *id, const struct hw_module_t **module)
这个id是hal层注册时加入的,例如sensor的hal的定义
struct sensors_module_t HAL_MODULE_INFO_SYM = {
    .common = {
        .tag = HARDWARE_MODULE_TAG,
        .version_major = 1,
        .version_minor = 0,
        .id = SENSORS_HARDWARE_MODULE_ID,
        .name = "MTK SENSORS Module",
        .author = "The Android Open Source Project",
        .methods = &sensors_module_methods,
    },
    .get_sensors_list = sensors__get_sensors_list,
};
#define SENSORS_HARDWARE_MODULE_ID "sensors"
hw_module_t是硬件模块结构,是HAL层的灵魂


下面来看hw_get_module是怎么去抓相应的HAL层硬件模块的
    for (i=0 ; i
        if (i < HAL_VARIANT_KEYS_COUNT) {
            if (property_get(variant_keys[i], prop, NULL) == 0) {
                continue;
            } /*获取ro.hardware/ro.product.board/ro.board.platform/ro.arch等key的值*/
            snprintf(path, sizeof(path), "%s/%s.%s.so",
                     HAL_LIBRARY_PATH2, name, prop) ; /*这个name是之前传进来的id,在我们这里就是"sensor",prop为之前抓取到的key信息,这里为mt6575*/
            if (access(path, R_OK) == 0) break;      /*下面的这几个函数在给定的几个目录中搜索我们要加载的库sensors.mt6575.so*/


            snprintf(path, sizeof(path), "%s/%s.%s.so",
                     HAL_LIBRARY_PATH1, name, prop);
            if (access(path, R_OK) == 0) break;


            snprintf(path, sizeof(path), "%s/%s.%s.so",
                     HAL_LIBRARY_PATH3, name, prop);
            if (access(path, R_OK) == 0) break;
        } else { /*如果上面没有收到,则用默认库*/
            snprintf(path, sizeof(path), "%s/%s.default.so",
                     HAL_LIBRARY_PATH1, name);
            if (access(path, R_OK) == 0) break;


            snprintf(path, sizeof(path), "%s/%s.default.so",
                     HAL_LIBRARY_PATH3, 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);
    }
找到这次需要加载的库后,即调用load函数
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); /*打开动态库*/
    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; /*被定义为"HMI"*/
    hmi = (struct hw_module_t *)dlsym(handle, sym); /*获取hw_module_t 结构体*/
    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) { /*对比hw_module_t结构体总的id和我们传进来的id是否一致,不一致的话直接退出*/
        LOGE("load: id=%s != hmi->id=%s", id, hmi->id);
        status = -EINVAL;
        goto done;
    }
    hmi->dso = handle;
    /* success */
    status = 0;
    *pHmi = hmi;/*返回结果*/
    return status;
}


通过readelf x.so来看看这个库的地址布局
Symbol table '.dynsym' contains 40 entries:
   Num:    Value  Size Type    Bind   Vis      Ndx Name
     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND 
     1: 000021d8   340 OBJECT  GLOBAL DEFAULT   15 sSensorList
     2: 00000000     0 FUNC    GLOBAL DEFAULT  UND __aeabi_unwind_cpp_pr0
     3: 00000000     0 FUNC    GLOBAL DEFAULT  UND __android_log_print
     4: 00000000     0 FUNC    GLOBAL DEFAULT  UND ioctl
     5: 00000000     0 FUNC    GLOBAL DEFAULT  UND __aeabi_ldivmod
     6: 00000000     0 FUNC    GLOBAL DEFAULT  UND __errno
     7: 00000000     0 FUNC    GLOBAL DEFAULT  UND __aeabi_unwind_cpp_pr1
     8: 00000000     0 FUNC    GLOBAL DEFAULT  UND malloc
     9: 00000000     0 FUNC    GLOBAL DEFAULT  UND memset
    10: 00000000     0 FUNC    GLOBAL DEFAULT  UND opendir
    11: 00000000     0 FUNC    GLOBAL DEFAULT  UND strcpy
    12: 00000000     0 FUNC    GLOBAL DEFAULT  UND strlen
    13: 00000000     0 FUNC    GLOBAL DEFAULT  UND open
    14: 00000000     0 FUNC    GLOBAL DEFAULT  UND strcmp
    15: 00000000     0 FUNC    GLOBAL DEFAULT  UND close
    16: 00000000     0 FUNC    GLOBAL DEFAULT  UND readdir
    17: 00000000     0 FUNC    GLOBAL DEFAULT  UND closedir
    18: 00000000     0 FUNC    GLOBAL DEFAULT  UND strerror
    19: 00000000     0 FUNC    GLOBAL DEFAULT  UND __stack_chk_fail
    20: 00000000     0 OBJECT  GLOBAL DEFAULT  UND __stack_chk_guard
    21: 00000000     0 FUNC    GLOBAL DEFAULT  UND free
    22: 00000000     0 FUNC    GLOBAL DEFAULT  UND memcpy
    23: 00000000     0 FUNC    GLOBAL DEFAULT  UND read
     24: 00002150   132 OBJECT  GLOBAL DEFAULT   15 HMI
    25: 00000000     0 FUNC    GLOBAL DEFAULT  UND __cxa_finalize
    26: 00002330     0 NOTYPE  GLOBAL DEFAULT   16 __dso_handle
    27: 00002000     0 NOTYPE  GLOBAL DEFAULT   11 __INIT_ARRAY__
    28: 00002008     0 NOTYPE  GLOBAL DEFAULT   12 __FINI_ARRAY__
    29: 000013d0     0 NOTYPE  GLOBAL DEFAULT  ABS __exidx_end
    30: 00001388     0 NOTYPE  GLOBAL DEFAULT  ABS __exidx_start
    31: 00002150     0 NOTYPE  GLOBAL DEFAULT   15 __data_start
    32: 0000232c     0 NOTYPE  GLOBAL DEFAULT  ABS _edata
    33: 0000232c     0 NOTYPE  GLOBAL DEFAULT  ABS __bss_start
    34: 0000232c     0 NOTYPE  GLOBAL DEFAULT  ABS __bss_start__
    35: 00002340     0 NOTYPE  GLOBAL DEFAULT  ABS _bss_end__
    36: 00002340     0 NOTYPE  GLOBAL DEFAULT  ABS __bss_end__
    37: 00002340     0 NOTYPE  GLOBAL DEFAULT  ABS __end__
    38: 00002340     0 NOTYPE  GLOBAL DEFAULT  ABS _end
    39: 00080000     0 NOTYPE  GLOBAL DEFAULT  ABS _stack
上面的"HMI"段就是我们之前定义的,即是hw_module_t结构体,每个hw_module_t的定义中名字都叫HAL_MODULE_INFO_SYM
实际上他还是由宏定义为"HMI"的


所以综上,可以得出,一个HAL模块也有一个入口地址,就是我们这里的hw_module_t结构体,通过它就可以把我们定义的接口给上层使用

你可能感兴趣的:(架构)