Android中hw_get_module函数分析

转自：http://hi.baidu.com/xdyang1986/blog/item/1681d3d4ef4a63d251da4bd5.html

这个函数的主要功能是根据模块ID寻找硬件模块动态链接库德地址，然后调用load去打开动态链接库并从中获取硬件模块结构体地址。具体的源码如下：

代码@/hardware/libhardware/hardware.c

int hw_get_module(const char *id, const struct hw_module_t **module)

120 {

121     int status;

122     int i;

123     const struct hw_module_t *hmi = NULL;

124     char prop[PATH_MAX];

125     char path[PATH_MAX];

    /* Loop through the configuration variants looking for a module */

135     for (i=0 ; i

/*

*这个地方我们来看一下下面将要用到的一个数组variant_keys，因为HAL_VARIANT_KEYS_COUNT这个就是

*数组variant_keys的大小。

*

*44 static const char *variant_keys[] = {

* 45     "ro.hardware",  /* This goes first so that it can pick up a different

* 46                        file on the emulator. */

* 47     "ro.product.board",

* 48     "ro.board.platform",

*  49     "ro.arch"

* 50 };

*这里我们记住这个数组，下面我就将用到它。

*/

136         if (i < HAL_VARIANT_KEYS_COUNT) {

137             if (property_get(variant_keys[i], prop, NULL) == 0) {

138                 continue;

139             }

/*

*这个地方prop得到的就似乎相应的权限，variant_keys[i]对应的如下：

*

*trout\msm7k\ARMV6就是这三个值，那个ro.hardware没有找到。这个地方我也是看注册的，没有弄懂

*知道的同学指教一些，谢谢。

*/

140             snprintf(path, sizeof(path), "%s/%s.%s.so",//把相应的路径及文件名保存到path中

141                     HAL_LIBRARY_PATH, id, prop);

/*

*看到没有，这个地方其实就是把HAL_LIBRARY_PATH/id.***.so保存到path中，其中***就是上面我们所分析的variant_keys各个元素所对应的值。

*/

142         } else {

/*

*这个地方就体现了为什么我们上面for循环用的是HAL_VARIANT_KEYS_COUNT+1而不是*HAL_VARIANT_KEYS_COUNT。因为我们在最后还有加载一个default的属性。

*/

143             snprintf(path, sizeof(path), "%s/%s.default.so",

144                     HAL_LIBRARY_PATH, id);

145         }

146         if (access(path, R_OK)) {

147             continue;

148         }

149         /* we found a library matching this id/variant */

150         break;

151     }

152

153     status = -ENOENT;

154     if (i < HAL_VARIANT_KEYS_COUNT+1) {

155         /* load the module, if this fails, we're doomed, and we should not try

156          * to load a different variant. */

157         status = load(id, path, module);//load相应库。并把它们的HMI保存到module中。//具体见西分析

158     }

159

  return status;

161 }

int hw_get_module(const char *id, const struct hw_module_t **module)

120 {

121     int status;

122     int i;

123     const struct hw_module_t *hmi = NULL;

124     char prop[PATH_MAX];

125     char path[PATH_MAX];

    /* Loop through the configuration variants looking for a module */

135     for (i=0 ; i





	 


	代码@/hardware/libhardware/hardware.c


	这个代码其实很简单。load相应库。并把它们的HMI保存到module中


	 


	
	
static int load(const char *id,

       const char *path,

       const struct hw_module_t **pHmi)

 {

      int status;

      void *handle;

      struct hw_module_t *hmi;

   handle = dlopen(path, RTLD_NOW);//打开相应的库

      if (handle == NULL) {

          char const *err_str = dlerror();

          LOGE("load: module=%s\n%s", path, err_str?err_str:"unknown");

         status = -EINVAL;

          goto done;

   }

static int load(const char *id,

       const char *path,

       const struct hw_module_t **pHmi)

 {

      int status;

      void *handle;

      struct hw_module_t *hmi;

   handle = dlopen(path, RTLD_NOW);//打开相应的库

      if (handle == NULL) {

          char const *err_str = dlerror();

          LOGE("load: module=%s\n%s", path, err_str?err_str:"unknown");

         status = -EINVAL;

          goto done;

   }



	 


	   


	
	
const char *sym = HAL_MODULE_INFO_SYM_AS_STR;

  hmi = (struct hw_module_t *)dlsym(handle, sym);//找到库中的HMI函数的地址（据snownight0102说，HMI不是一个函数，我还不是很清楚，等待解释）

     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) {//只是一个check

      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;//把这个返回过去

    return status;

 }

const char *sym = HAL_MODULE_INFO_SYM_AS_STR;

  hmi = (struct hw_module_t *)dlsym(handle, sym);//找到库中的HMI函数的地址（据snownight0102说，HMI不是一个函数，我还不是很清楚，等待解释）

     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) {//只是一个check

      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;//把这个返回过去

    return status;

 }



	以上为转载


	以下为hardware/libhardware/hardware.c


	
	
/*
 * 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
 *
 *
 *
 * 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

#include

#include
#include
#include
#include
#include

#define LOG_TAG "HAL"
#include

/** Base path of the hal modules */
#define HAL_LIBRARY_PATH "/system/lib/hw"

/**
 * There are a set of variant filename for modules. The form of the filename
 * is ".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(const char *id, 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];

    /*
     * 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
        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_PATH, id, prop);
        } else {
            snprintf(path, sizeof(path), "%s/%s.default.so",
                    HAL_LIBRARY_PATH, id);
        }
        if (access(path, R_OK)) {
            continue;
        }
        /* we found a library matching this id/variant */
        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(id, path, module);
    }

    return status;
}

/*
 * 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
 *
 *      
 *
 * 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 

#include 

#include 
#include 
#include 
#include 
#include 

#define LOG_TAG "HAL"
#include 

/** Base path of the hal modules */
#define HAL_LIBRARY_PATH "/system/lib/hw"

/**
 * There are a set of variant filename for modules. The form of the filename
 * is ".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(const char *id, 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];

    /*
     * 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