IClass与电源管理

IClass与电源管理

前段时间为J9项目上添加电源管理，中间走了一些弯路。之前错误的认为，IClass只是与电源状态的改变方法有关，也就是说IClass的正确与否只会影响到设备电源状态的正确与否，而不会造成设备是否可以支持设备电源状态的转换。

结果后来整USB的时候，发现完全不是这么回事，郁闷了两天。

担心忘记了，电源管理中与IClass相关知识赶紧写下来。

一．PM中的相关内容说明

1．结构体DEVICE_LIST

首先看一下结构体DEVICE_LIST的定义：

// this structure describes a set of power manageable devices

typedef struct _DeviceList_tag {

LPCGUID pGuid; // class of device

PDEVICE_STATE pList; // pointer to devices

HANDLE hMsgQ; // device notification queue

HANDLE hnClass; // handle from RequestDeviceNotifications()

PDEVICE_INTERFACE pInterface; // interface to the device class power management routines

struct _DeviceList_tag *pNext; // singly linked list pointer

} DEVICE_LIST, *PDEVICE_LIST;

可以看到其第一个成员pGuid指向了GUID的名字，大家都知道CE中的PM相关GUID有四个，分别是通用设备，网络设备，块设备和GWES设备。默认在注册表[HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Control/Power/Interfaces]下进行声明，它是通过PM.dll中的相关宏定义进行指定，可以将PM Driver移植到BSP下后进行修改。

典型的定义如下：

; Power Manager interfaces. These list the interface classes that the Power

; Manager will monitor for new devices.

;

[HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Control/Power/Interfaces]

"{A32942B7-920C-486b-B0E6-92A702A99B35}"="Generic power-manageable devices"

"{8DD679CE-8AB4-43c8-A14A-EA4963FAA715}"="Power-manageable block devices"

; @CESYSGEN IF CE_MODULES_NDIS

"{98C5250D-C29A-4985-AE5F-AFE5367E5006}"="Power-manageable NDIS miniports"

; @CESYSGEN ENDIF CE_MODULES_NDIS

; @CESYSGEN IF CE_MODULES_GWES

"{EB91C7C9-8BF6-4a2d-9AB8-69724EED97D1}"="Power-manageable display"

; @CESYSGEN ENDIF CE_MODULES_GWES

显然，系统中应当维护着4个DEVICE_LIST结构体变量，它们最终组成一个单向链表，通过全局变量gpDeviceLists指向其表头，该链表在函数DeviceListsInit()中进行初始化，而DeviceListsInit()由PmInit()进行调用。

2．结构体DEVICE_STATE

首先看一下结构体DEVICE_STATE的定义：

// this structure describes a power-manageable device

typedef struct _DeviceState_tag {

LPCTSTR pszName; // device's name

CEDEVICE_POWER_STATE curDx; // current official power state (not necessarily supported by the device)

CEDEVICE_POWER_STATE floorDx; // minimum device power state, or PwrDeviceUnspecified

CEDEVICE_POWER_STATE ceilingDx; // maximum device power state, or PwrDeviceUnspecified

CEDEVICE_POWER_STATE setDx; // power state if explicitly set, or PwrDeviceUnspecified

CEDEVICE_POWER_STATE lastReqDx; // last state requested by the device

CEDEVICE_POWER_STATE actualDx; // current actual device power state

CEDEVICE_POWER_STATE pendingDx; // Pending DX for updating

DWORD dwNumPending; // Number of Pending for updating.

struct _DeviceState_tag *pParent; // parent device, or NULL

POWER_CAPABILITIES caps; // as reported by the device

DWORD dwRefCount; // structure can be deallocated when this is 0

HANDLE hDevice; // handle to the device from OpenDevice(), or NULL

PDEVICE_INTERFACE pInterface; // interface to the device class power management routines

struct _DeviceList_tag *pListHead; // pointer to the containing list

struct _DeviceState_tag *pNext; // linked list pointers

struct _DeviceState_tag *pPrev;

} DEVICE_STATE, *PDEVICE_STATE;

可以看到，该链表是一个双向链表，可以通过其前向和后驱双向遍历。

每一个由Device.exe（6.0下应该是kernel.exe）/GWES加载的设备以及网络和通用设备都对应一个该结构体的变量。

每一类GUID设备会组成一个DEVICE_STATE链表，也就是说系统中最大只有四个这种链表，通过结构体DEVICE_LIST的pList成员进行指向。

好了，现在你可以知道要找到一个设备的DEVICE_STATE的方法了，就是先找到它对应的GUID类的DEVICE_LIST结构体，然后从该类结构体的pList里面遍历特定的设备名找到你的DEVICE_STATE结点。

系统中已经实现了该函数，即GetDeviceListFromClass和DeviceStateFindList。GetDeviceListFromClass代码如下：

// this routine determines to which device list a particular device class

// corresponds

PDEVICE_LIST

GetDeviceListFromClass(LPCGUID guidDevClass)

{

PDEVICE_LIST pdl;

SETFNAME(_T("GetDeviceListFromClass"));

PREFAST_DEBUGCHK(guidDevClass != NULL);

// look for a match

__try {

for(pdl = gpDeviceLists; pdl != NULL; pdl = pdl->pNext) {

if(*pdl->pGuid == *guidDevClass) {

break;

}

__except(EXCEPTION_EXECUTE_HANDLER) {

PMLOGMSG(TRUE, (_T("%s: exception accessing guidDevClass 0x%08x/r/n"),

pszFname, guidDevClass));

pdl = NULL;

}

return pdl;

}

DeviceStateFindList代码如下：

// This routine looks for a device on a list. If it finds the device, it

// increments its reference counter and returns a pointer to it. The caller

// should decrement the reference counter when it is done with the pointer.

// Note that the search is case sensitive.

PDEVICE_STATE

DeviceStateFindList(PDEVICE_LIST pdl, LPCTSTR pszName)

{

PDEVICE_STATE pds;

SETFNAME(_T("DeviceStateFindList"));

PMLOCK();

__try {

// look for a match

for(pds = pdl->pList; pds != NULL; pds = pds->pNext) {

if(_tcscmp(pds->pszName, pszName) == 0) {

// increment the reference count and exit

DeviceStateAddRef(pds);

break;

}

__except(EXCEPTION_EXECUTE_HANDLER) {

PMLOGMSG(ZONE_WARN, (_T("%s: exception searching list/r/n"), pszFname));

pds = NULL;

}

PMUNLOCK();

return pds;

}

3．指针函数结构体DEVICE_INTERFACE

首先看一下结构体DEVICE_INTERFACE的定义：

typedef struct _DeviceInterface_tag {

BOOL (WINAPI * pfnInitInterface) (VOID);

HANDLE (WINAPI *pfnOpenDevice) (struct _DeviceState_tag *);

BOOL (WINAPI * pfnCloseDevice) (HANDLE);

BOOL (WINAPI * pfnRequestDevice) (HANDLE, DWORD, LPVOID, DWORD, LPVOID, DWORD, LPDWORD);

} DEVICE_INTERFACE, *PDEVICE_INTERFACE;

系统中共维护两个该结构体的变量，即PM的MDD层Driver中定义的gStreamInterface和gDisplayInterface。

其中，gDisplayInterface对应的GWES加载的设备，而gStreamInterface对应的是网络设备，块驱动设备和通用设备。

其各个成员的意思就不再赘述。

二．IClass在电源管理中的用途

1．PM的相关初始化

1> 谁加载了PM.dll

在CE5.0中，设备管理器是Device.exe，到6.0里面由于单个Process空间上了GB的级别，就将其改为Device.dll，挂在了Kernel.exe里面。惭愧的是对于6.0，小弟始终没有找到在哪里LoadLibrary(“Device.dll”)。

小弟猜测应该是Filesys加载的PM.dll，帮助文档中讲述Filesys的启动过程的时候也没有提到这点，但是由于Filesys并没有源码，不知道各位有没有比较好的方法可以验证这一点。

2> PM的初始化

Filesys.exe/Filesys.dll调用了Device.exe/Device.dll的导出函数StartDeviceManager()，而在函数StartDeviceManager()中调用了PM.dll导出的初始化函数PmInit()。

PmInit()首先调用DeviceListsInit()去查询注册表的配置并初始化DEVICE_LIST链表。函数DeviceListsInit()的代码如下：

// This routine reads the registry to determine what type of device interfaces

// we will be monitoring. The default PM GUID is ignored if present in the

// registry and is always added last (so it's first in the list).

BOOL

DeviceListsInit(VOID)

{

BOOL fOk = TRUE;

PDEVICE_LIST pdl;

DWORD dwStatus;

HKEY hk;

TCHAR szBuf[MAX_PATH];

SETFNAME(_T("DeviceListsInit"));

// enumerate all the device classes

// 到注册表[HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Control/Power/Interfaces]下

// 获取GUID的值，默认情况下，ICLASS共有类别，此处直接通过枚举的方式查询到每一个GUID

wsprintf(szBuf, _T("%s//Interfaces"), PWRMGR_REG_KEY);

dwStatus = RegOpenKeyEx(HKEY_LOCAL_MACHINE, szBuf, 0, 0, &hk);

if(dwStatus == ERROR_SUCCESS) {

DWORD dwIndex = 0;

do {

DWORD cbValueName = dim(szBuf), dwType;

GUID idInterface;

dwStatus = RegEnumValue(hk, dwIndex, szBuf, &cbValueName, NULL,

&dwType, NULL, NULL);

if(dwStatus == ERROR_SUCCESS) {

if(dwType != REG_SZ) {

PMLOGMSG(ZONE_WARN, (_T("%s: invalid type for value '%s'/r/n"),

pszFname, szBuf));

}

// 将GUID进行转换

else if(!ConvertStringToGuid(szBuf, &idInterface)) {

PMLOGMSG(ZONE_WARN, (_T("%s: can't convert '%s' to GUID/r/n"),

pszFname, szBuf));

}

// 如果是通用设备的GUID，则跳过，留到最后进行初始化其DEVICE_LIST

else if(idInterface == idGenericPMDeviceClass) {

PMLOGMSG(ZONE_INIT, (_T("%s: default GUID found in registry as expected/r/n"),

pszFname));

}

// 为特定GUID类分配并初始化一个DEVICE_LIST结构体变量

else if((pdl = DeviceListCreate(&idInterface)) == NULL) {

PMLOGMSG(ZONE_WARN, (_T("%s: DeviceListCreate() failed/r/n"),

pszFname));

}

// 初始化上面分配的DEVICE_LIST结构体变量的成员pInterface，使其指向有效的函数指针结构体

// 函数PlatformDeviceListInit这里非常重要，它初始化了DEVICE_LIST结构体变量的成员pInterface，而pInterface的具体实现包括gDisplayInterface和gStreamInterface，在pmstream.cpp和pmdisplay.cpp可以找到其具体的实现，代码写的蛮经典的

// 这些函数指针结构体通过PM Driver的MDD层获得

else if(PlatformDeviceListInit(pdl) == FALSE) {

PMLOGMSG(ZONE_WARN, (_T("%s: PlatformDeviceListInit() failed/r/n"),

pszFname));

DeviceListDestroy(pdl);

}

// 将当前GUID的DEVICE_LIST结构体变量添加链表gpDeviceLists中

else {

// add the new entry to the list

pdl->pNext = gpDeviceLists;

gpDeviceLists = pdl;

}

// update the index

dwIndex++;

}

} while(dwStatus == ERROR_SUCCESS);

// check for abnormal termination of the loop

if(dwStatus != ERROR_NO_MORE_ITEMS) {

fOk = FALSE;

}

// close the registry handle

RegCloseKey(hk);

}

// add the default list last

// 通用设备类留在最后进行初始化，为什么？

// 主要是为了让通用设备类保持在gpDeviceLists的最前面，利于后面的处理

if(fOk) {

fOk = FALSE;

pdl = DeviceListCreate(&idGenericPMDeviceClass);

if(pdl != NULL) {

if(PlatformDeviceListInit(pdl) == FALSE) {

PMLOGMSG(ZONE_INIT || ZONE_WARN,

(_T("%s: PlatformDeviceListInit() failed for default class/r/n"),

pszFname));

DeviceListDestroy(pdl);

} else {

pdl->pNext = gpDeviceLists;

gpDeviceLists = pdl;

fOk = TRUE;

}

// clean up if necessary

if(!fOk) {

PMLOGMSG(ZONE_WARN, (_T("%s: error during list initialization/r/n"),

pszFname));

while(gpDeviceLists != NULL) {

pdl = gpDeviceLists;

gpDeviceLists = pdl->pNext;

pdl->pNext = NULL;

DeviceListDestroy(pdl);

}

return fOk;

}

接下来PmInit会去创建线程PnpThreadProc，该线程非常重要，它主要来检测系统中地新加载的设备。虽然其名字是PNP，但是其服务对象不仅仅是PNP设备，迷惑了我十几分钟。

PnpThreadProc的优先级可以通过注册表项PnPPriority256去进行配置，如果没有配置，将采用默认的249。

// this thread waits for power manageable devices to be announced. When

// they arrive they are added to the PM's list of devices and initialized

// appropriately. If a device goes away, its entry will be removed

// from the list.

DWORD WINAPI

PnpThreadProc(LPVOID lpvParam)

{

DWORD dwStatus;

HANDLE hnGeneric = NULL;

HANDLE hevReady = (HANDLE) lpvParam;

HANDLE hEvents[MAXIMUM_WAIT_OBJECTS];

DWORD dwNumEvents = 0;

BOOL fDone = FALSE;

BOOL fOk;

INT iPriority;

PDEVICE_LIST pdl;

SETFNAME(_T("PnpThreadProc"));

PMLOGMSG(ZONE_INIT, (_T("+%s: thread 0x%08x/r/n"), pszFname, GetCurrentThreadId()));

// set the thread priority

if(!GetPMThreadPriority(_T("PnPPriority256"), &iPriority)) {

iPriority = DEF_PNP_THREAD_PRIORITY;

}

CeSetThreadPriority(GetCurrentThread(), iPriority);

// first list entry is the exit event

hEvents[dwNumEvents++] = ghevPmShutdown;

// set up device notifications

for(pdl = gpDeviceLists; pdl != NULL && dwNumEvents < dim(hEvents); pdl = pdl->pNext) {

hEvents[dwNumEvents++] = pdl->hMsgQ;

// 有几个GUID类别，就申请几个通知

pdl->hnClass = RequestDeviceNotifications(pdl->pGuid, pdl->hMsgQ, TRUE);

if(pdl->hnClass == NULL) {

PMLOGMSG(ZONE_WARN, (_T("%s: RequestDeviceNotifications() failed %d/r/n"),

pszFname, GetLastError()));

}

DEBUGCHK(dwNumEvents > 1);

// we're up and running

SetEvent(hevReady);

// wait for new devices to arrive

while(!fDone) {

dwStatus = WaitForMultipleObjects(dwNumEvents, hEvents, FALSE, INFINITE);

if(dwStatus == (WAIT_OBJECT_0 + 0)) {

PMLOGMSG(ZONE_WARN, (_T("%s: shutdown event set/r/n"), pszFname));

fDone = TRUE;

} else if(dwStatus > WAIT_OBJECT_0 && dwStatus <= (WAIT_OBJECT_0 + MAXIMUM_WAIT_OBJECTS)) {

dwStatus -= WAIT_OBJECT_0;

// 收到通知就就对特定GUID设备的电源状态进行获取

fOk = ProcessPnPMsgQueue(hEvents[dwStatus]);

if(!fOk) {

PMLOGMSG(ZONE_WARN, (_T("%s: ProcessPnPMsgQueue(0x%08x) failed/r/n"), pszFname,

hEvents[dwStatus]));

}

} else {

PMLOGMSG(ZONE_WARN, (_T("%s: WaitForMultipleObjects() returned %d, status is %d/r/n"),

pszFname, dwStatus, GetLastError()));

fDone = TRUE;

break;

}

// release resources

for(pdl = gpDeviceLists; pdl != NULL; pdl = pdl->pNext) {

if(pdl->hnClass != NULL) StopDeviceNotifications(pdl->hnClass);

}

// all done

PMLOGMSG(ZONE_INIT | ZONE_WARN, (_T("-%s: exiting/r/n"), pszFname));

return 0;

}

可以上面可以看到，线程PnpThreadProc只会侦测链表gpDeviceLists中创建的GUID类设备的通知，而gpDeviceLists是由函数DeviceListsInit()中进行初始化的。也就是说，PM最终所能够识别的设备是那些在注册表[HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet

/Control/Power/Interfaces]下定义的GUID类，这也是为什么设备支持电源管理的话必须定义IClass。

当然，理论上来讲，你可以修改注册表，添加一种新的GUID类，并ReWrite PM的代码，使其支持你所添加的GUID类设备。

2．PM获取新加载设备所支持电源状态过程

从上面函数PnpThreadProc()中可以看到，当侦测到有新设备通知发出来后，将会调用函数ProcessPnPMsgQueue()。

函数ProcessPnPMsgQueue()完成的功能是获取设备所支持的电源状态，方式是调用MDD层提供的函数RequestStreamDevice或者RequestDisplayDevice。再说的具体一点就是，分别调用到设备驱动中的DeviceIoControl和ExtEscape。

请看函数ProcessPnPMsgQueue()的代码：

// This routine adds a device to the list associated with its device class.

// This routine does not return a value; it will either create a new

// device state structure and add it to a list or it will not. If the new

// device duplicates an existing one this routine won't create a new node.

// This routine executes in the context of the PnP thread, which handles

// device interface additions and removals.

VOID

AddDevice(LPCGUID guidDevClass, LPCTSTR pszName, PDEVICE_STATE pdsParent,

PPOWER_CAPABILITIES pCaps)

{

SETFNAME(_T("AddDevice"));

PMLOGMSG(ZONE_DEVICE,

(_T("%s: adding '%s', pdsParent 0x%08x, pCaps 0x%08x to class %08x-%04x-%04x-%04x-%02x%02x%02x%02x%02x%02x/r/n"),

pszFname, pszName, pdsParent, pCaps,

guidDevClass->Data1, guidDevClass->Data2, guidDevClass->Data3,

(guidDevClass->Data4[0] << 8) + guidDevClass->Data4[1], guidDevClass->Data4[2], guidDevClass->Data4[3],

guidDevClass->Data4[4], guidDevClass->Data4[5], guidDevClass->Data4[6], guidDevClass->Data4[7]));

// figure out onto which list this device should be added

// 到DEVICE_LIST链表中查询当前设备所在的GUID类对应的DEVICE_LIST指针

PDEVICE_LIST pdl = GetDeviceListFromClass(guidDevClass);

// did we find the list?

if(pdl != NULL) {

// check for duplicates

// 到当前设备所对应的DEVICE_LIST链表中查询是否在名字为pszName的设备

PDEVICE_STATE pds = DeviceStateFindList(pdl, pszName);

// create the device if it doesn't already exist

// 如果不存在，则创建一个

if(pds == NULL) {

BOOL fOk = FALSE;

// 为当前设备创建一个DEVICE_STATE节点

pds = DeviceStateCreate(pszName);

if(pds != NULL) {

// if we are passed the device's capabilities, just copy them

// into the structure

if(pCaps != NULL) {

__try {

pds->caps = *pCaps;

}

__except(EXCEPTION_EXECUTE_HANDLER) {

PMLOGMSG(ZONE_WARN,

(_T("%s: exception during capabilities copy from 0x%08x/r/n"),

pszFname, pCaps));

pCaps = NULL;

}

// update the device's parent pointer

if(pdsParent != NULL) {

DeviceStateAddRef(pdsParent);

}

pds->pParent = pdsParent;

// add the new device to its class list

// 将当前设备的DEVICE_STATE加入到guidDevClass对应的DEVICE_LIST链表中

if(!DeviceStateAddList(pdl, pds)) {

// deallocate the node, reference count isn't incremented

DeviceStateDecRef(pds);

pds = NULL;

} else {

PREFAST_DEBUGCHK(pds->pInterface != NULL);

PREFAST_DEBUGCHK(pds->pInterface->pfnOpenDevice != NULL);

PREFAST_DEBUGCHK(pds->pInterface->pfnRequestDevice != NULL);

PREFAST_DEBUGCHK(pds->pInterface->pfnCloseDevice != NULL);

// 获取设备的操作Handle，这里比较重要，调用的其实是MDD层中首先的函数OpenStreamDevice或者OpenDisplayDevice

pds->hDevice = pds->pInterface->pfnOpenDevice(pds);

if(pds->hDevice == INVALID_HANDLE_VALUE) {

PMLOGMSG(ZONE_WARN, (_T("%s: couldn't open device '%s'/r/n"),

pszFname, pszName != NULL ? _T("<NULL>") : pszName));

} else {

// do we need to request capabilities?

fOk = TRUE; // assume success

if(pCaps == NULL) {

DWORD dwBytesReturned;

POWER_RELATIONSHIP pr;

PPOWER_RELATIONSHIP ppr = NULL;

memset(&pr, 0, sizeof(pr));

if(pds->pParent != NULL) {

PMLOGMSG(ZONE_DEVICE, (_T("%s: parent of '%s' is '%s'/r/n"),

pszFname, pds->pszName, pds->pParent->pszName));

pr.hParent = (HANDLE) pds->pParent;

pr.pwsParent = pds->pParent->pszName;

pr.hChild = (HANDLE) pds;

pr.pwsChild = pds->pszName;

ppr = &pr;

}

// get the device's capabilities structure

// 有点意思了，呵呵，调用IOCTL_POWER_CAPABILITIES获取设备所支持的电源状态这里比较重要，调用的其实是MDD层中首先的函数RequestStreamDevice或者RequestDisplayDevice，对于这两类设备来说，分别调用到设备驱动中的DeviceIoControl和ExtEscape

fOk = pds->pInterface->pfnRequestDevice(pds->hDevice, IOCTL_POWER_CAPABILITIES,

ppr, ppr == NULL ? 0 : sizeof(*ppr),

&pds->caps, sizeof(pds->caps), &dwBytesReturned);

// sanity check the size in case a device is just returning

// a good status on all ioctls for some reason

if(fOk && dwBytesReturned != sizeof(pds->caps)) {

PMLOGMSG(ZONE_WARN,

(_T("%s: invalid size returned from IOCTL_POWER_CAPABILITIES/r/n"),

pszFname));

fOk = FALSE;

}

// any problems so far?

if(fOk) {

// determine whether we should request power relationships from a parent device

// 帮助文档中提到，这里的意思是：

// Set to POWER_CAP_PARENT bit if the device would like to receive an IOCTL_REGISTER_POWER_RELATIONSHIP call after initialization

// BSP中并没有使用，应该不用关注

if((pds->caps.Flags & POWER_CAP_PARENT) != 0) {

pds->pInterface->pfnRequestDevice(pds->hDevice, IOCTL_REGISTER_POWER_RELATIONSHIP,

NULL, 0, NULL, 0, NULL);

}

// have we read all the configuration information we need from

// the new device

if(!fOk) {

// no, delete the device

DeviceStateRemList(pds);

} else {

// See if the device supports multiple handles. Power manageable devices

// should allow multiple open handles, but if they don't we will have to open

// one before each access.

HANDLE hDevice = pds->pInterface->pfnOpenDevice(pds);

if(hDevice == INVALID_HANDLE_VALUE) {

PMLOGMSG(ZONE_WARN, (_T("%s: WARNING: '%s' does not support multiple handles/r/n"),

pszFname));

pds->pInterface->pfnCloseDevice(pds->hDevice);

pds->hDevice = INVALID_HANDLE_VALUE;

} else {

// close the second handle, since we don't need it

pds->pInterface->pfnCloseDevice(hDevice);

}

// initialize the new device's power state variables

// 这里就不用说了，更新电源状态，呵呵

UpdateDeviceState(pds);

}

// we are done with the device pointer

if(pds != NULL) {

DeviceStateDecRef(pds);

}

} else {

PMLOGMSG(ZONE_WARN, (_T("%s: class for device '%s' not supported/r/n"),

pszFname, pszName));

}

3．IClass对AP层面的影响

这个比较简单，可以参照Help文档，如下：

Beginning with Windows CE .NET 4.10, power-manageable devices can belong to varying device classes. These device classes consist both of predefined classes as well as custom device classes. The Power Manager APIs that accept device names can also accept class-qualified device names. For example, each of the following names is a valid device name:

· COM1:

· {A32942B7-920C-486b-B0E6-92A702A99B35}/COM1:

· {98C5250D-C29A-4985-AE5F-AFE5367E5006}/CISCO1

· {8DD679CE-8AB4-43c8-A14A-EA4963FAA715}/DSK1:

If a class does not qualify a device name, the device is assumed to belong to the default device class. For example, the names COM1: and {A32942B7-920C-486b-B0E6-92A702A99B35}/COM1: are equivalent.

可以看到，AP调用PM的API尝试去获取或者改变设备的电源状态的时候，需要传入争取地Device name，如果传入的Device name不包含IClass的话，系统将其认为是默认的IClass类，也就是{A32942B7-920C-486b-B0E6-92A702A99B35}。