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

[Tomoki Sekiyama]

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.

> 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