camera hw_get_module
google为了保护硬件厂商的信息，在Android中添加了一层，也就是大名鼎鼎的HAL层。
HAL的编写方法的过程中，会发现整个模块貌似没有一个入口。一般说来模块都要有个入口，比
如应用程序有main函数，可以为加载器进行加载执行，dll文件有dllmain，而对于我们自己写的动态
链接库，我们可以对库中导出的任何符号进行调用。
问题来了，Android中的HAL是比较具有通用性的，需要上层的函数对其进行加载调用，Android的
HAL加载器是如何实现对不同的Hardware Module进行通用性的调用的呢？
带着这个疑问查看Android源码，会发现Android中实现调用HAL是通过hw_get_module实现的
int hw_get_module(const char *id, const struct hw_module_t **module)
{
return hw_get_module_by_class(id, NULL, module); //id:camera
}
int hw_get_module_by_class(const char *class_id, const char *inst,
const struct hw_module_t **module)
{
int i = 0;
char prop[PATH_MAX] = {0};
char path[PATH_MAX] = {0};
char name[PATH_MAX] = {0};
char prop_name[PATH_MAX] = {0};
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.
*/
/* First try a property specific to the class and possibly instance */
snprintf(prop_name, sizeof(prop_name), "ro.hardware.%s", name);//ro.hardware.camera
if (property_get(prop_name, prop, NULL) > 0) { //prop:sp9832e
if (hw_module_exists(path, sizeof(path), name, prop) == 0) {
goto found;
}
}
/* Loop through the configuration variants looking for a module */
for (i=0 ; i
continue;
}
if (hw_module_exists(path, sizeof(path), name, prop) == 0) {
goto found;
}
}
/* Nothing found, try the default */
if (hw_module_exists(path, sizeof(path), name, "default") == 0) {
goto found;
}
return -ENOENT;
found:
/* load the module, if this fails, we're doomed, and we should not try
* to load a different variant. */
return load(class_id, path, module);//path:vendor/lib/hw/camera.sp9832e.so class_id：camera
}
#if defined(__LP64__)
#define HAL_LIBRARY_PATH1 "/system/lib64/hw"
#define HAL_LIBRARY_PATH2 "/vendor/lib64/hw"
#define HAL_LIBRARY_PATH3 "/odm/lib64/hw"
#else
#define HAL_LIBRARY_PATH1 "/system/lib/hw"
#define HAL_LIBRARY_PATH2 "/vendor/lib/hw"
#define HAL_LIBRARY_PATH3 "/odm/lib/hw"
#endif
static int hw_module_exists(char *path, size_t path_len, const char *name,
const char *subname)
{
snprintf(path, path_len, "%s/%s.%s.so",
HAL_LIBRARY_PATH3, name, subname);
if (path_in_path(path, HAL_LIBRARY_PATH3) && access(path, R_OK) == 0)
return 0;
snprintf(path, path_len, "%s/%s.%s.so",
HAL_LIBRARY_PATH2, name, subname);/vendor/lib/hw/camera.sp9832e.so
if (path_in_path(path, HAL_LIBRARY_PATH2) && access(path, R_OK) == 0)
return 0;
#ifndef __ANDROID_VNDK__
snprintf(path, path_len, "%s/%s.%s.so",
HAL_LIBRARY_PATH1, name, subname);
if (path_in_path(path, HAL_LIBRARY_PATH1) && access(path, R_OK) == 0)
return 0;
#endif
return -ENOENT;
}
static int load(const char *id,
const char *path,
const struct hw_module_t **pHmi)
{
int status = -EINVAL;
void *handle = NULL;
struct hw_module_t *hmi = NULL;
#ifdef __ANDROID_VNDK__
const bool try_system = false;
#else
const bool try_system = true;
#endif
/*
* 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
*/
if (try_system &&
strncmp(path, HAL_LIBRARY_PATH1, strlen(HAL_LIBRARY_PATH1)) == 0) {
/* If the library is in system partition, no need to check
* sphal namespace. Open it with dlopen.
*/
handle = dlopen(path, RTLD_NOW);
} else {
#if defined(__ANDROID_RECOVERY__)
handle = dlopen(path, RTLD_NOW);
#else
handle = android_load_sphal_library(path, RTLD_NOW);
#endif
}
if (handle == NULL) {
char const *err_str = dlerror();
ALOGE("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) {
ALOGE("load: couldn't find symbol %s", sym);
status = -EINVAL;
goto done;
}
/* Check that the id matches */
if (strcmp(id, hmi->id) != 0) {
ALOGE("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 {
ALOGV("loaded HAL id=%s path=%s hmi=%p handle=%p",
id, path, hmi, handle);
}
*pHmi = hmi;
return status;
}
const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
hmi = (struct hw_module_t *)dlsym(handle, sym);
QCamera2Hal.cpp
static hw_module_t camera_common = {
.tag = HARDWARE_MODULE_TAG,
.module_api_version = CAMERA_MODULE_API_VERSION_2_5,
.hal_api_version = HARDWARE_HAL_API_VERSION,
.id = CAMERA_HARDWARE_MODULE_ID,
.name = "QCamera Module",
.author = "Qualcomm Innovation Center Inc",
.methods = &qcamera::QCamera2Factory::mModuleMethods,
.dso = NULL,
.reserved = {0}
};
camera_module_t HAL_MODULE_INFO_SYM = {
.common = camera_common,
.get_number_of_cameras = qcamera::QCamera2Factory::get_number_of_cameras,
.get_physical_camera_info = qcamera::QCamera2Factory::get_physical_camera_info,
.is_stream_combination_supported = qcamera::QCamera2Factory::is_stream_combination_supported,
.get_camera_info = qcamera::QCamera2Factory::get_camera_info,
.set_callbacks = qcamera::QCamera2Factory::set_callbacks,
.get_vendor_tag_ops = qcamera::QCamera3VendorTags::get_vendor_tag_ops,
.open_legacy = NULL,
.set_torch_mode = qcamera::QCamera2Factory::set_torch_mode,
.init = NULL,
.reserved = {0}
参考led: https://blog.csdn.net/mdx20072419/article/details/10354651