Android AudioFlinger載入HAL層流程
一、前提
Audio HAL層最終以.so的方式為Android所用,那這個.so的庫如何被AudioFlinger所使用?
二、Audio Hardware HAL載入
(1)AudioFlinger
AudioFlinger載入HAL層:
static int load_audio_interface(const char *if_name, const hw_module_t **mod,
audio_hw_device_t **dev)
{
int rc;
/* 這裡載入的是音訊動態庫,如audio.primary.msm8916.so,如何載入會獨立體現 */
rc = hw_get_module_by_class(AUDIO_HARDWARE_MODULE_ID, if_name, mod);
if (rc)
goto out;
//載入好的動態庫模組必有個open方法,呼叫open方法開啟音訊裝置模組
rc = audio_hw_device_open(*mod, dev);
LOGE_IF(rc, "couldn't open audio hw device in %s.%s (%s)",
AUDIO_HARDWARE_MODULE_ID, if_name, strerror(-rc));
if (rc)
goto out;
return 0;
out:
*mod = NULL;
*dev = NULL;
return rc;
}
audio_interface:
/* hw_get_module_by_class需要根據這些字串找到相關的音訊模組庫 */
static const char *audio_interfaces[] = {
"primary", //指本機中的codec
"a2dp", //a2dp裝置,藍芽高保真音訊
"usb", //usb-audio裝置
};
AudioFlinger::onFirstRef:
void AudioFlinger::onFirstRef()
{
int rc = 0;
Mutex::Autolock _l(mLock);
/* TODO: move all this work into an Init() function */
mHardwareStatus = AUDIO_HW_IDLE;
//開啟audio_interfaces陣列定義的所有音訊裝置
for (size_t i = 0; i < ARRAY_SIZE(audio_interfaces); i++) {
const hw_module_t *mod;
audio_hw_device_t *dev;
rc = load_audio_interface(audio_interfaces[i], &mod, &dev);
if (rc)
continue;
LOGI("Loaded %s audio interface from %s (%s)", audio_interfaces[i],
mod->name, mod->id);
mAudioHwDevs.push(dev); //mAudioHwDevs是一個Vector,儲存已開啟的audio hw devices
if (!mPrimaryHardwareDev) {
mPrimaryHardwareDev = dev;
LOGI("Using '%s' (%s.%s) as the primary audio interface",
mod->name, mod->id, audio_interfaces[i]);
}
}
mHardwareStatus = AUDIO_HW_INIT;
if (!mPrimaryHardwareDev || mAudioHwDevs.size() == 0) {
LOGE("Primary audio interface not found");
return;
}
//對audio hw devices進行一些初始化,如mode、master volume的設定
for (size_t i = 0; i < mAudioHwDevs.size(); i++) {
audio_hw_device_t *dev = mAudioHwDevs[i];
mHardwareStatus = AUDIO_HW_INIT;
rc = dev->init_check(dev);
if (rc == 0) {
AutoMutex lock(mHardwareLock);
mMode = AUDIO_MODE_NORMAL;
mHardwareStatus = AUDIO_HW_SET_MODE;
dev->set_mode(dev, mMode);
mHardwareStatus = AUDIO_HW_SET_MASTER_VOLUME;
dev->set_master_volume(dev, 1.0f);
mHardwareStatus = AUDIO_HW_IDLE;
}
}
}
主要是通過hw_get_module_by_class()找到模組介面名字if_name相匹配的模組庫,載入之後audio_hw_device_open()呼叫模組的open方法,完成音訊裝置模組的初始化。
hw_get_module_by_class:
hw_get_module_by_class實現在hardware/libhardware/ hardware.c中,它作用載入指定名字的模組庫(.so檔案)。
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);
//這裡我們以音訊庫為例,AudioFlinger呼叫到這個函式時,
//class_id=AUDIO_HARDWARE_MODULE_ID="audio",inst="primary"(或"a2dp"或"usb")
//那麼此時name="audio.primary"
/*
* 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) {
/* 通過property_get找到廠家標記如"ro.product.board=msm8916",這時prop="msm8916" */
if (property_get(variant_keys[i], prop, NULL) == 0) {
continue;
}
/* #define HAL_LIBRARY_PATH2 "/vendor/lib/hw" */
snprintf(path, sizeof(path), "%s/%s.%s.so",
HAL_LIBRARY_PATH2, name, prop);
if (access(path, R_OK) == 0) break;
/* #define HAL_LIBRARY_PATH1 "/system/lib/hw" */
snprintf(path, sizeof(path), "%s/%s.%s.so",
HAL_LIBRARY_PATH1, name, prop);
if (access(path, R_OK) == 0) break;
} else {
/* 如沒有指定的庫檔案,則載入default.so */
snprintf(path, sizeof(path), "%s/%s.default.so",
HAL_LIBRARY_PATH1, name);
if (access(path, R_OK) == 0) break;
}
}
/** 到這裡,完成一個模組庫的完整路徑名稱,如path="/system/lib/hw/audio.primary.msm8916.so" */
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. */
//載入模組庫:見下面
status = load(class_id, path, module);
}
return status;
}
load(class_id, path, module):
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;
}
在開啟的.so(audio.primary.msm8916.so)中查詢HMI符號的地址,並儲存在hmi中。至此.so中的hw_module_t已經被成功獲取。從而可以根據它獲取HAL層相關介面。
- HAL通過hw_get_module函式獲取hw_module_t
- HAL通過hw_module_t->methods->open獲取hw_device_t指標,並在此open函式中初始化audio_hw_device_t結構中的函式。
- 三個重要的資料結構:
a) struct hw_device_t: 表示硬體裝置,儲存了各種硬體裝置的公共屬性和方法
b)struct hw_module_t: 可用hw_get_module進行載入的module
c)struct hw_module_methods_t: 用於定義操作裝置的方法,其中只定義了一個開啟裝置的方法open.
hw_module_t定義:
/**
* 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 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;
在load(…)中dlsym拿到這個結構體的首地址後,就可以呼叫Modules methods進行裝置模組的初始化了。裝置模組中,都應該按照這個格式初始化好這個結構體,否則dlsym找不到它,也就無法呼叫Modules methods進行初始化了。
audio_hw.c中hw_module_methods_t 的例項化:
static struct hw_module_methods_t hal_module_methods = {
.open = adev_open,
};
struct audio_module HAL_MODULE_INFO_SYM = {
.common = {
.tag = HARDWARE_MODULE_TAG,
.version_major = 1,
.version_minor = 0,
.id = AUDIO_HARDWARE_MODULE_ID,
.name = "Tuna audio HW HAL",
.author = "The Android Open Source Project",
.methods = &hal_module_methods,
},
};
audio_module 是我們Audio HAL必須要實現的。
audio_hw_device 介面
介面按照hardware/libhardware/include/hardware/audio.h定義的介面實現就行了。這些介面全扔到一個結構體裡面的,這樣做的好處是:不必用大量的dlsym來獲取各個介面函式的地址,只需找到這個結構體即可,從易用性和可擴充性來說,都是首選方式。
audio_hw_device 介面如下:
struct audio_hw_device {
struct hw_device_t common;
/**
* used by audio flinger to enumerate what devices are supported by
* each audio_hw_device implementation.
*
* Return value is a bitmask of 1 or more values of audio_devices_t
*/
uint32_t (*get_supported_devices)(const struct audio_hw_device *dev);
/**
* check to see if the audio hardware interface has been initialized.
* returns 0 on success, -ENODEV on failure.
*/
int (*init_check)(const struct audio_hw_device *dev);
/** set the audio volume of a voice call. Range is between 0.0 and 1.0 */
int (*set_voice_volume)(struct audio_hw_device *dev, float volume);
/**
* set the audio volume for all audio activities other than voice call.
* Range between 0.0 and 1.0. If any value other than 0 is returned,
* the software mixer will emulate this capability.
*/
int (*set_master_volume)(struct audio_hw_device *dev, float volume);
/**
* setMode is called when the audio mode changes. AUDIO_MODE_NORMAL mode
* is for standard audio playback, AUDIO_MODE_RINGTONE when a ringtone is
* playing, and AUDIO_MODE_IN_CALL when a call is in progress.
*/
int (*set_mode)(struct audio_hw_device *dev, int mode);
/* mic mute */
int (*set_mic_mute)(struct audio_hw_device *dev, bool state);
int (*get_mic_mute)(const struct audio_hw_device *dev, bool *state);
/* set/get global audio parameters */
int (*set_parameters)(struct audio_hw_device *dev, const char *kv_pairs);
/*
* Returns a pointer to a heap allocated string. The caller is responsible
* for freeing the memory for it.
*/
char * (*get_parameters)(const struct audio_hw_device *dev,
const char *keys);
/* Returns audio input buffer size according to parameters passed or
* 0 if one of the parameters is not supported
*/
size_t (*get_input_buffer_size)(const struct audio_hw_device *dev,
uint32_t sample_rate, int format,
int channel_count);
/** This method creates and opens the audio hardware output stream */
int (*open_output_stream)(struct audio_hw_device *dev, uint32_t devices,
int *format, uint32_t *channels,
uint32_t *sample_rate,
struct audio_stream_out **out);
void (*close_output_stream)(struct audio_hw_device *dev,
struct audio_stream_out* out);
/** This method creates and opens the audio hardware input stream */
int (*open_input_stream)(struct audio_hw_device *dev, uint32_t devices,
int *format, uint32_t *channels,
uint32_t *sample_rate,
audio_in_acoustics_t acoustics,
struct audio_stream_in **stream_in);
void (*close_input_stream)(struct audio_hw_device *dev,
struct audio_stream_in *in);
/** This method dumps the state of the audio hardware */
int (*dump)(const struct audio_hw_device *dev, int fd);
};
typedef struct audio_hw_device audio_hw_device_t;
在HAL層adev_open初始化中要對audio_hw_device 進行賦值初始化,HAL層的重頭戲其實就是對這些函式進行例項化。
HAL層之後就會呼叫Tinyalsa,接著就是Audio Driver了。
總體順序:AudioFlinger->Audio HAL->Tinyalsa->Audio Driver。