Re: [Qemu-devel] [PATCH v4 06/10] qemu-ga: Add Windows VSS provider to quiesce applications on fsfreeze

[Paolo Bonzini]

Il 26/06/2013 00:31, Tomoki Sekiyama ha scritto:
> From: Paolo Bonzini address@hidden on behalf of Paolo Bonzini address@hidden
>> Il 06/06/2013 17:06, Tomoki Sekiyama ha scritto:
>>> +STDAPI VSSCheckOSVersion(void);
>>> +
>>> +STDAPI COMRegister(void);
>>> +STDAPI COMUnregister(void);
>>> +
>>> +STDAPI DllRegisterServer(void);
>>> +STDAPI DllUnregisterServer(void);
>>
>> Can you explain the difference between COMRegister/COMUnregister and
>> DllRegisterServer/DllUnregisterServer (and why the COM+ part need not be
>> done by regsvr32)?  Also, why does COMUnregister call
>> DllUnregisterServer but COMRegister does not call DllRegisterServer?
> 
> COMRegister and COMUnregister are called by`qemu-ga -s install`,
> to register/unregister the DLL into/from COM+ application catalogue.
> 
> DllRegisterServer is automatically called inside
> pCatalog->InstallComponent() (like regsvr32 does), and register
> this DLL as a VSS provider. DllUnregisterServer will do the oposite.
> 
> ICOMAdminCatalog (pCatalog) does not provide a method to uninstall
> component, so COMUnregister calls DllUnregisterServer by itself.

Understood, thanks.  Just one question remains: why is the COM+ part not
needed when you invoke regsvr32?

Thanks,

Paolo

>> Also, is it needed to call VSSCheckOSVersion from the requestor?  I
>> would think that checking VSSAPI.DLL is stronger than checking the
>> version, and indeed you do that check too.
> 
> In Windows XP, VSSAPI.DLL exists but it has different functionality
> and interfaces from newer Windows. 
> http://msdn.microsoft.com/en-us/library/windows/desktop/aa384627(v=vs.85).aspx
> 
> It is checking the OS version because this patchset only supports
> Windows 2003 or later.
> 
> Thanks,
> Tomoki Sekiyama
>