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

[Laszlo Ersek]

On 06/25/13 18:03, Laszlo Ersek wrote:
> On 06/06/13 17:06, Tomoki Sekiyama wrote:

Comparing the .def file and the provider header file:

>> diff --git a/qga/vss-win32-provider/qga-provider.def 
>> b/qga/vss-win32-provider/qga-provider.def
>> new file mode 100644
>> index 0000000..9f3afc8
>> --- /dev/null
>> +++ b/qga/vss-win32-provider/qga-provider.def
>> @@ -0,0 +1,10 @@
>> +LIBRARY      "QGA-PROVIDER.DLL"
>> +
>> +EXPORTS
>> +    VSSCheckOSVersion       PRIVATE
>> +    COMRegister             PRIVATE
>> +    COMUnregister           PRIVATE
>> +    DllCanUnloadNow         PRIVATE
>> +    DllGetClassObject       PRIVATE
>> +    DllRegisterServer       PRIVATE
>> +    DllUnregisterServer     PRIVATE

>> diff --git a/qga/vss-win32-provider.h b/qga/vss-win32-provider.h
>> new file mode 100644
>> index 0000000..a437e71
>> --- /dev/null
>> +++ b/qga/vss-win32-provider.h
>> @@ -0,0 +1,26 @@
>> +/*
>> + * QEMU Guest Agent win32 VSS provider declarations
>> + *
>> + * Copyright Hitachi Data Systems Corp. 2013
>> + *
>> + * Authors:
>> + *  Tomoki Sekiyama   <address@hidden>
>> + *
>> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
>> + * See the COPYING file in the top-level directory.
>> + */
>> +
>> +#ifndef VSS_WIN32_PROVIDER_H
>> +#define VSS_WIN32_PROVIDER_H
>> +
>> +#include <windows.h>
>> +
>> +STDAPI VSSCheckOSVersion(void);
>> +
>> +STDAPI COMRegister(void);
>> +STDAPI COMUnregister(void);
>> +
>> +STDAPI DllRegisterServer(void);
>> +STDAPI DllUnregisterServer(void);
>> +
>> +#endif

(a) what is the reason for not listing DllCanUnloadNow() and
DllGetClassObject() in the header file?

(b) Does STDAPI imply a return type? Or are you just going with the
implicit "int"? (Based on my encounters with EFIAPI, I think it's the
latter.)


>> diff --git a/qga/vss-win32.h b/qga/vss-win32.h
>> new file mode 100644
>> index 0000000..21655cf
>> --- /dev/null
>> +++ b/qga/vss-win32.h
>> @@ -0,0 +1,86 @@
>> +/*
>> + * QEMU Guest Agent win32 VSS common declarations
>> + *
>> + * Copyright Hitachi Data Systems Corp. 2013
>> + *
>> + * Authors:
>> + *  Tomoki Sekiyama   <address@hidden>
>> + *
>> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
>> + * See the COPYING file in the top-level directory.
>> + */
>> +
>> +#ifndef VSS_WIN32_H
>> +#define VSS_WIN32_H
>> +
>> +#define __MIDL_user_allocate_free_DEFINED__
>> +#include "config-host.h"
>> +#include <windows.h>
>> +#include <shlwapi.h>
>> +
>> +/* Reduce warnings to include vss.h */
>> +
>> +/* Ignore annotations for MS IDE */
>> +#define __in  IN
>> +#define __out OUT
>> +#define __RPC_unique_pointer
>> +#define __RPC_string
>> +#define __RPC__deref_inout_opt
>> +#define __RPC__out
>> +#ifndef __RPC__out_ecount_part
>> +#define __RPC__out_ecount_part(x, y)
>> +#endif
>> +#define _declspec(x)
>> +#undef uuid
>> +#define uuid(x)
>> +
>> +/* Undef some duplicated error codes redefined in vss.h */
>> +#undef VSS_E_BAD_STATE
>> +#undef VSS_E_PROVIDER_NOT_REGISTERED
>> +#undef VSS_E_PROVIDER_VETO
>> +#undef VSS_E_OBJECT_NOT_FOUND
>> +#undef VSS_E_VOLUME_NOT_SUPPORTED
>> +#undef VSS_E_VOLUME_NOT_SUPPORTED_BY_PROVIDER
>> +#undef VSS_E_OBJECT_ALREADY_EXISTS
>> +#undef VSS_E_UNEXPECTED_PROVIDER_ERROR
>> +#undef VSS_E_INVALID_XML_DOCUMENT
>> +#undef VSS_E_MAXIMUM_NUMBER_OF_VOLUMES_REACHED
>> +#undef VSS_E_MAXIMUM_NUMBER_OF_SNAPSHOTS_REACHED
>> +
>> +/*
>> + * VSS headers must be installed from Microsoft VSS SDK 7.2 available at:
>> + * http://www.microsoft.com/en-us/download/details.aspx?id=23490
>> + */
>> +#include "inc/win2003/vss.h"
>> +
>> +/* Macros to convert char definitions to wchar */
>> +#define _L(a) L##a
>> +#define L(a) _L(a)

(Sigh. The more windows code I'm looking at the more it convinces me
that EFI was 100% meant for windows originally. Sad.)


>> +
>> +/* Constants for QGA VSS Provider */
>> +
>> +#define QGA_PROVIDER_NAME "QEMU Guest Agent VSS Provider"
>> +#define QGA_PROVIDER_LNAME L(QGA_PROVIDER_NAME)
>> +#define QGA_PROVIDER_VERSION L(QEMU_VERSION)
>> +
>> +#define EVENT_NAME_FROZEN "Global\\QGAVSSEvent-frozen"
>> +#define EVENT_NAME_THAW   "Global\\QGAVSSEvent-thaw"

No idea what I'm talking about, but since we're qualifying the second
component with the "QGAVSSEvent" prefix, shouldn't we just replace the
first component ("Global") with it? Or would it effect "event routing"?
(Tangential question, anyway.)


>> +
>> +const GUID g_gProviderId = { 0x3629d4ed, 0xee09, 0x4e0e,
>> +    {0x9a, 0x5c, 0x6d, 0x8b, 0xa2, 0x87, 0x2a, 0xef} };
>> +const GUID g_gProviderVersion = { 0x11ef8b15, 0xcac6, 0x40d6,
>> +    {0x8d, 0x5c, 0x8f, 0xfc, 0x16, 0x3f, 0x24, 0xca} };
>> +
>> +const CLSID CLSID_QGAVSSProvider = { 0x6e6a3492, 0x8d4d, 0x440c,
>> +    {0x96, 0x19, 0x5e, 0x5d, 0x0c, 0xc3, 0x1c, 0xa8} };
>> +
>> +const TCHAR g_szClsid[] = TEXT("{6E6A3492-8D4D-440C-9619-5E5D0CC31CA8}");

OK, these match each other and "qga-provider.idl".


>> +const TCHAR g_szProgid[] = TEXT("QGAVSSProvider");
>> +
>> +/* Enums undefined in VSS SDK 7.2 but defined in newer Windows SDK */
>> +enum __VSS_VOLUME_SNAPSHOT_ATTRIBUTES {
>> +    VSS_VOLSNAP_ATTR_NO_AUTORECOVERY       = 0x00000002,
>> +    VSS_VOLSNAP_ATTR_TXF_RECOVERY          = 0x02000000
>> +};
>> +
>> +#endif
>>
>>

OK.


>> diff --git a/qga/vss-win32-provider/install.cpp 
>> b/qga/vss-win32-provider/install.cpp
>> new file mode 100644
>> index 0000000..d6f1d55
>> --- /dev/null
>> +++ b/qga/vss-win32-provider/install.cpp
>> @@ -0,0 +1,493 @@
>> +/*
>> + * QEMU Guest Agent win32 VSS Provider installer
>> + *
>> + * Copyright Hitachi Data Systems Corp. 2013
>> + *
>> + * Authors:
>> + *  Tomoki Sekiyama   <address@hidden>
>> + *
>> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
>> + * See the COPYING file in the top-level directory.
>> + */
>> +
>> +#include <stdio.h>
>> +#include <string.h>
>> +
>> +#include "../vss-win32.h"
>> +#include "inc/win2003/vscoordint.h"
>> +#include "../vss-win32-provider.h"
>> +
>> +#include <comadmin.h>
>> +#include <wbemidl.h>
>> +#include <comutil.h>
>> +
>> +extern HINSTANCE g_hinstDll;
>> +
>> +const GUID CLSID_COMAdminCatalog = { 0xF618C514, 0xDFB8, 0x11d1,
>> +    {0xA2, 0xCF, 0x00, 0x80, 0x5F, 0xC7, 0x92, 0x35} };
>> +const GUID IID_ICOMAdminCatalog = { 0xDD662187, 0xDFC2, 0x11d1,
>> +    {0xA2, 0xCF, 0x00, 0x80, 0x5F, 0xC7, 0x92, 0x35} };
>> +const GUID CLSID_WbemLocator = { 0x4590f811, 0x1d3a, 0x11d0,
>> +    {0x89, 0x1f, 0x00, 0xaa, 0x00, 0x4b, 0x2e, 0x24} };
>> +const GUID IID_IWbemLocator = { 0xdc12a687, 0x737f, 0x11cf,
>> +    {0x88, 0x4d, 0x00, 0xaa, 0x00, 0x4b, 0x2e, 0x24} };

Would it be possible to make these static? Not too important of course.


>> +
>> +static void errmsg(DWORD err, const char *text)
>> +{
>> +    char *msg = NULL, *nul = strchr(text, '(');
>> +    int len = nul ? nul - text : -1;
>> +
>> +    FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
>> +                  FORMAT_MESSAGE_FROM_SYSTEM | 
>> FORMAT_MESSAGE_IGNORE_INSERTS,
>> +                  NULL, err, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
>> +                  (char *)&msg, 0, NULL);

(The FormatMessage() specification in MSDN is simply incredible.
"(char *)&msg", seriously? Your code is correct, but the interface is
unbelievable.)


>> +    printf("%.*s. (Error: %lx) %s\n", len, text, err, msg);

(a) Since we're printing an error message here, I suspect it should go
to stderr.

(b) In case "text" doesn't contain an opening paren, "len" is set to -1.
"A negative precision is taken as if the precision were omitted", IOW
the entire string will be printed. Clever!

(c) Does DWORD expand to "uint32_t"? In that case "%lx" is too big on
64-bit (LP64). We should probably use "%x" or "%"PRIx32. (Or do we build
qemu-ga.exe only for 32-bit? I seem to remember something like that.)


>> +    LocalFree(msg);
>> +}
>> +
>> +static void errmsg_dialog(DWORD err, const char *text, const char *opt = "")
>> +{
>> +    char *msg, buf[512];
>> +
>> +    FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
>> +                  FORMAT_MESSAGE_FROM_SYSTEM | 
>> FORMAT_MESSAGE_IGNORE_INSERTS,
>> +                  NULL, err, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
>> +                  (char *)&msg, 0, NULL);
>> +    snprintf(buf, sizeof(buf), "%s%s. (Error: %lx) %s\n", text, opt, err, 
>> msg);
>> +    MessageBox(NULL, buf, "Error from " QGA_PROVIDER_NAME, 
>> MB_OK|MB_ICONERROR);

Do you need a trailing newline for a message box?


>> +    LocalFree(msg);
>> +}
>> +
>> +#define _chk(hr, status, msg, err_label)        \
>> +    do {                                        \
>> +        hr = (status);                          \
>> +        if (FAILED(hr)) {                       \
>> +            errmsg(hr, msg);                    \
>> +            goto err_label;                     \
>> +        }                                       \
>> +    } while (0)
>> +
>> +#define chk(status) _chk(hr, status, "Failed to " #status, out)
>> +
>> +template<class T>
>> +HRESULT put_Value(ICatalogObject *pObj, LPCWSTR name, T val)
>> +{
>> +    return pObj->put_Value(_bstr_t(name), _variant_t(val));
>> +}
>> +
>> +/* Check whether this OS version supports VSS providers */
>> +STDAPI VSSCheckOSVersion(void)
>> +{
>> +    OSVERSIONINFO OSver;
>> +
>> +    OSver.dwOSVersionInfoSize = sizeof(OSVERSIONINFO);
>> +    GetVersionEx(&OSver);
>> +    if ((OSver.dwMajorVersion == 5 && OSver.dwMinorVersion >= 2) ||
>> +       OSver.dwMajorVersion > 5) {
>> +        return S_OK;
>> +    }
>> +    return S_FALSE;
>> +}
>> +

Seems OK.


>> +/* Lookup Administrators group name from winmgmt */
>> +static HRESULT GetAdminName(_bstr_t &name)
>> +{

I can see that you want to call GetAdminName() in chk(), hence you must
return a HRESULT and store the value through the parameter list.
However, can we keep the C++ features to a minimum? I'd prefer if the
non-const reference were replaced with a pointer-to-_bstr_t.
(Tangential, change only if you respin anyway and don't mind it.)


>> +    HRESULT hr;
>> +    IWbemLocator *pLoc = NULL;
>> +    IWbemServices *pSvc = NULL;
>> +    IEnumWbemClassObject *pEnum = NULL;
>> +    IWbemClassObject *pWobj = NULL;
>> +    ULONG returned;
>> +    _variant_t var;
>> +
>> +    chk(CoCreateInstance(CLSID_WbemLocator, NULL, CLSCTX_INPROC_SERVER,
>> +                         IID_IWbemLocator, (LPVOID *)&pLoc));
>> +    chk(pLoc->ConnectServer(_bstr_t(L"ROOT\\CIMV2"), NULL, NULL, NULL,
>> +                            0, 0, 0, &pSvc));
>> +    chk(CoSetProxyBlanket(pSvc, RPC_C_AUTHN_WINNT, RPC_C_AUTHZ_NONE,
>> +                          NULL, RPC_C_AUTHN_LEVEL_CALL,
>> +                          RPC_C_IMP_LEVEL_IMPERSONATE, NULL, EOAC_NONE));
>> +    chk(pSvc->ExecQuery(_bstr_t(L"WQL"),
>> +                        _bstr_t(L"select * from Win32_Account where "
>> +                                "SID='S-1-5-32-544' and localAccount=TRUE"),
>> +                        WBEM_FLAG_RETURN_IMMEDIATELY | 
>> WBEM_FLAG_FORWARD_ONLY,
>> +                        NULL, &pEnum));

(signal to noise ratio converging to zero... :) I don't doubt this is
the official way though.)

Furthermore, aren't you missing a CoInitialize(NULL) call before
CoCreateInstance()? Other CoCreateInstance() calls are preceded by it.

... Well this is called only from COMRegister(), after such an init
call, so it should be OK.


>> +    if (!pEnum) {
>> +        errmsg(E_FAIL, "Failed to query for Administrators");
>> +        goto out;

I think you forgot to set "hr" to something ugly -- the code below the
"out" label will simply return it, and "hr" is currently something nice.
(The last chk() succeeded.)


>> +    }

This branch is probably for the case when ExecQuery() succeeds, but
doesn't return any rows, right?


>> +    chk(pEnum->Next(WBEM_INFINITE, 1, &pWobj, &returned));
>> +    if (returned == 0) {
>> +        errmsg(E_FAIL, "Failed to query for Administrators");
>> +        goto out;
>> +    }
>> +
>> +    chk(pWobj->Get(_bstr_t(L"Name"), 0, &var, 0, 0));
>> +    name = var;

This assigns a _variant_t to a _bstr_t (... for which I proposed *name =
var above, but it's irrelevant now).

Can this conversion (or the assignment operator) fail? If so, does
either throw an exception?


>> +out:
>> +    if (pLoc) {
>> +        pLoc->Release();
>> +    }
>> +    if (pSvc) {
>> +        pSvc->Release();
>> +    }
>> +    if (pEnum) {
>> +        pEnum->Release();
>> +    }
>> +    if (pWobj) {
>> +        pWobj->Release();
>> +    }
>> +    return hr;
>> +}

I'm sure this is idiomatic code, but do these pointers point to static /
long-term instances? I'm missing the equivalent of "delete pLoc" and so
on. Each Release() member function gets the implicit "this" parameter
here, but do they free it too? (Honestly, I can't decide which would be
worse, if they did or they didn't.)

... Ah, it's probably reference counting. OK.


>> +
>> +/* Register this module to COM+ Applications Catalog */
>> +STDAPI COMRegister(void)
>> +{
>> +    HRESULT hr = E_FAIL;
>> +    IUnknown *pUnknown = NULL;
>> +    ICOMAdminCatalog *pCatalog = NULL;
>> +    ICatalogCollection *pApps = NULL, *pRoles = NULL, *pUsersInRole = NULL;
>> +    ICatalogObject *pObj = NULL;
>> +    long n;
>> +    _bstr_t name;
>> +    _variant_t key;
>> +    CHAR dllPath[MAX_PATH], tlbPath[MAX_PATH];
>> +
>> +    if (!g_hinstDll) {
>> +        errmsg(E_FAIL, "Failed to initialize DLL");
>> +        goto out;

OK, "hr" is E_FAIL here.


>> +    }
>> +
>> +    if (VSSCheckOSVersion() == S_FALSE) {
>> +        printf("VSS provider is not supported in this OS version.\n");

I suggest stderr.


>> +        return S_FALSE; /* VSS feature is disabled */

Somewhat inconsistent with the above, you issue "return" although you
used "goto out" before. No resources are leaked so it's no problem in
practice. (You could have written "return" above.)


>> +    }
>> +
>> +    COMUnregister();

What requires / justifies this? (I can see another call below, on the
error path.) I think whatever COMUnregister() would release depends
first on the success of COMRegister(), doesn't it?

You've told Paolo,

On 06/26/13 00:31, Tomoki Sekiyama wrote:
> COMRegister and COMUnregister are called by`qemu-ga -s install`,
> to register/unregister the DLL into/from COM+ application catalogue.

and indeed I can see a COMRegister() call in 09/10. Nonetheless that
doesn't seem to justify this call to COMUnregister() -- if the DLL has
been previously registered in the application catalog, a new
registration attempt should fail.


>> +
>> +    chk(CoInitialize(NULL));

Can this fail in practice? If so, we could have error handling trouble,
because "out:" will call CoUninitialize() without any successful
initialization.


>> +    chk(CoCreateInstance(CLSID_COMAdminCatalog, NULL, CLSCTX_INPROC_SERVER,
>> +                         IID_IUnknown, (void **)&pUnknown));
>> +    chk(pUnknown->QueryInterface(IID_ICOMAdminCatalog, (void **)&pCatalog));
>> +
>> +    /* Install COM+ Component */
>> +
>> +    chk(pCatalog->GetCollection(_bstr_t(L"Applications"),
>> +                                (IDispatch **)&pApps));
>> +    chk(pApps->Populate());
>> +    chk(pApps->Add((IDispatch **)&pObj));
>> +    chk(put_Value(pObj, L"Name",        QGA_PROVIDER_LNAME));
>> +    chk(put_Value(pObj, L"Description", QGA_PROVIDER_LNAME));
>> +    chk(put_Value(pObj, L"ApplicationAccessChecksEnabled", true));
>> +    chk(put_Value(pObj, L"Authentication",                 short(6)));
>> +    chk(put_Value(pObj, L"AuthenticationCapability",       short(2)));
>> +    chk(put_Value(pObj, L"ImpersonationLevel",             short(2)));
>> +    chk(pApps->SaveChanges(&n));

This looks like a globally visible change that is not rolled back if
something fails later in this function. Is the COMUnregister() call on
the error handling path supposed to undo these? Complicated :)

Then, should we check "n", or does the retval check suffice?


>> +    chk(pObj->get_Key(&key));
>> +
>> +    pObj->Release();
>> +    pObj = NULL;

Ah OK. You're reusing pObj below.


>> +
>> +    if (!GetModuleFileName(g_hinstDll, dllPath, sizeof(dllPath))) {
>> +        errmsg(GetLastError(), "GetModuleFileName failed");
>> +        goto out;

"hr" has not been set to a failure code.


>> +    }
>> +    n = strlen(dllPath);
>> +    if (n < 3) {
>> +        errmsg(E_FAIL, "Failed to lookup dll");

Presumably you wanted to set "hr" and jump to "out" as well.


>> +    }
>> +    strcpy(tlbPath, dllPath);
>> +    strcpy(tlbPath+n-3, "TLB");
>> +    printf("Registering " QGA_PROVIDER_NAME ":\n");
>> +    printf("  %s\n", dllPath);
>> +    printf("  %s\n", tlbPath);

These are arguably diagnostic messages (destined for stderr), but I
won't press it :)


>> +    if (!PathFileExists(tlbPath)) {
>> +        errmsg(ERROR_FILE_NOT_FOUND, "Failed to lookup tlb");
>> +        goto out;

"hr" not set properly.


>> +    }
>> +
>> +    chk(pCatalog->InstallComponent(_bstr_t(QGA_PROVIDER_LNAME),
>> +                                   _bstr_t(dllPath), _bstr_t(tlbPath),
>> +                                   _bstr_t("")));
>> +
>> +    /* Setup roles of the applicaion */
>> +
>> +    chk(pApps->GetCollection(_bstr_t(L"Roles"), key,
>> +                             (IDispatch **)&pRoles));
>> +    chk(pRoles->Populate());
>> +    chk(pRoles->Add((IDispatch **)&pObj));
>> +    chk(put_Value(pObj, L"Name",        L"Administrators"));
>> +    chk(put_Value(pObj, L"Description", L"Administrators group"));
>> +    chk(pRoles->SaveChanges(&n));
>> +    chk(pObj->get_Key(&key));
>> +
>> +    pObj->Release();
>> +    pObj = NULL;
>> +
>> +    /* Setup users in the role */
>> +
>> +    chk(pRoles->GetCollection(_bstr_t(L"UsersInRole"), key,
>> +                              (IDispatch **)&pUsersInRole));
>> +    chk(pUsersInRole->Populate());
>> +
>> +    chk(pUsersInRole->Add((IDispatch **)&pObj));
>> +    chk(GetAdminName(name));
>> +    chk(put_Value(pObj, L"User", _bstr_t(".\\") + name));
>> +
>> +    pObj->Release();
>> +    pObj = NULL;
>> +
>> +    chk(pUsersInRole->Add((IDispatch **)&pObj));
>> +    chk(put_Value(pObj, L"User", L"SYSTEM"));
>> +    chk(pUsersInRole->SaveChanges(&n));
>> +
>> +out:
>> +    if (pUnknown) {
>> +        pUnknown->Release();
>> +    }
>> +    if (pCatalog) {
>> +        pCatalog->Release();
>> +    }
>> +    if (pApps) {
>> +        pApps->Release();
>> +    }
>> +    if (pRoles) {
>> +        pRoles->Release();
>> +    }
>> +    if (pUsersInRole) {
>> +        pUsersInRole->Release();
>> +    }
>> +    if (pObj) {
>> +        pObj->Release();
>> +    }
>> +
>> +    if (FAILED(hr)) {
>> +        COMUnregister();

I've actually grown to accept this COMUnregister() call here... Undoing
all the crap from before staircase-wise would be a nightmare.


>> +    }
>> +    CoUninitialize();

Another question: can you nest CoInitialize() calls (and more
importantly, does CoUninitialize() respect that)? Consider the following
call chain:

COMRegister()
  CoInitialize()
  COMUnregister() -- on the "out:" path
    DllUnregisterServer()
      CoInitialize() -- init after init
      CoUninitialize()
    CoInitialize()
    CoUninitialize()
  CoUninitialize() -- right here, uninit after uninit

Will these work (especially the final two)?


>> +
>> +    return hr;
>> +}
>> +
>> +/* Unregister this module from COM+ Applications Catalog */
>> +STDAPI COMUnregister(void)
>> +{
>> +    HRESULT hr;
>> +    IUnknown *pUnknown = NULL;
>> +    ICOMAdminCatalog *pCatalog = NULL;
>> +    ICatalogCollection *pColl = NULL;
>> +    ICatalogObject *pObj = NULL;
>> +    _variant_t var;
>> +    long i, n;
>> +
>> +    if (VSSCheckOSVersion() == S_FALSE) {
>> +        printf("VSS provider is not supported in this OS version.\n");

I suggest stderr again.


>> +        return S_FALSE; /* VSS feature is disabled */
>> +    }
>> +
>> +    chk(DllUnregisterServer());

Apparently DllUnregisterServer() can't fail. (And it shouldn't, we
depend on it, since COMUnregister() is also used as destructor after
partial construction, so we must not bail here.) I propose to change the
return type of DllUnregisterServer() to void, just to drive the point
home.


>> +
>> +    chk(CoInitialize(NULL));

(same question as before -- can this fail? See unconditional uninit at
the bottom.)

I'll continue from here.

Thanks
Laszlo


>> +    chk(CoCreateInstance(CLSID_COMAdminCatalog, NULL, CLSCTX_INPROC_SERVER,
>> +                         IID_IUnknown, (void **)&pUnknown));
>> +    chk(pUnknown->QueryInterface(IID_ICOMAdminCatalog, (void **)&pCatalog));
>> +
>> +    chk(pCatalog->GetCollection(_bstr_t(L"Applications"),
>> +                                (IDispatch **)&pColl));
>> +    chk(pColl->Populate());
>> +
>> +    chk(pColl->get_Count(&n));
>> +    for (i = n - 1; i >= 0; i--) {
>> +        chk(pColl->get_Item(i, (IDispatch **)&pObj));
>> +        chk(pObj->get_Value(_bstr_t(L"Name"), &var));
>> +        if (var == _variant_t(QGA_PROVIDER_LNAME)) {
>> +            printf("Removing COM+ Application: %S\n", (wchar_t 
>> *)_bstr_t(var));
>> +            chk(pColl->Remove(i));
>> +        }
>> +    }
>> +    chk(pColl->SaveChanges(&n));
>> +
>> +out:
>> +    if (pUnknown) {
>> +        pUnknown->Release();
>> +    }
>> +    if (pCatalog) {
>> +        pCatalog->Release();
>> +    }
>> +    if (pColl) {
>> +        pColl->Release();
>> +    }
>> +    if (pObj) {
>> +        pObj->Release();
>> +    }
>> +    CoUninitialize();
>> +
>> +    return hr;
>> +}
>> +
>> +
>> +static BOOL CreateRegistryKey(LPCTSTR key, LPCTSTR value, LPCTSTR data)
>> +{
>> +    HKEY  hKey;
>> +    LONG  ret;
>> +    DWORD size;
>> +
>> +    ret = RegCreateKeyEx(HKEY_CLASSES_ROOT, key, 0, NULL,
>> +        REG_OPTION_NON_VOLATILE, KEY_WRITE, NULL, &hKey, NULL);
>> +    if (ret != ERROR_SUCCESS) {
>> +        goto out;
>> +    }
>> +
>> +    if (data != NULL) {
>> +        size = (lstrlen(data) + 1) * sizeof(TCHAR);
>> +    } else {
>> +        size = 0;
>> +    }
>> +
>> +    ret = RegSetValueEx(hKey, value, 0, REG_SZ, (LPBYTE)data, size);
>> +    RegCloseKey(hKey);
>> +
>> +out:
>> +    if (ret != ERROR_SUCCESS) {
>> +        /* We cannot printf here, and need MessageBox to report an error. */
>> +        errmsg_dialog(ret, "Cannot add registry ", key);
>> +        return FALSE;
>> +    }
>> +    return TRUE;
>> +}
>> +
>> +/* Register this dll as a VSS provider */
>> +STDAPI DllRegisterServer(void)
>> +{
>> +    IVssAdmin *pVssAdmin = NULL;
>> +    HRESULT hr = E_FAIL;
>> +    char dllPath[MAX_PATH];
>> +    char key[256];
>> +
>> +    CoInitialize(NULL);
>> +
>> +    if (!g_hinstDll) {
>> +        errmsg_dialog(hr, "Module instance is not available");
>> +        goto out;
>> +    }
>> +
>> +    /* Add this module to registery */
>> +
>> +    sprintf(key, "CLSID\\%s", g_szClsid);
>> +    if (!CreateRegistryKey(key, NULL, g_szClsid)) {
>> +        goto out;
>> +    }
>> +
>> +    if (!GetModuleFileName(g_hinstDll, dllPath, sizeof(dllPath))) {
>> +        errmsg_dialog(GetLastError(), "GetModuleFileName failed");
>> +        goto out;
>> +    }
>> +    sprintf(key, "CLSID\\%s\\InprocServer32", g_szClsid);
>> +    if (!CreateRegistryKey(key, NULL, dllPath)) {
>> +        goto out;
>> +    }
>> +
>> +    sprintf(key, "CLSID\\%s\\InprocServer32", g_szClsid);
>> +    if (!CreateRegistryKey(key, "ThreadingModel", "Apartment")) {
>> +        goto out;
>> +    }
>> +
>> +    sprintf(key, "CLSID\\%s\\ProgID", g_szClsid);
>> +    if (!CreateRegistryKey(key, NULL, g_szProgid)) {
>> +        goto out;
>> +    }
>> +
>> +    if (!CreateRegistryKey(g_szProgid, NULL, QGA_PROVIDER_NAME)) {
>> +        goto out;
>> +    }
>> +
>> +    sprintf(key, "%s\\CLSID", g_szProgid);
>> +    if (!CreateRegistryKey(key, NULL, g_szClsid)) {
>> +        goto out;
>> +    }
>> +
>> +    hr = CoCreateInstance(CLSID_VSSCoordinator,
>> +        NULL, CLSCTX_ALL, IID_IVssAdmin, (void **)&pVssAdmin);
>> +    if (FAILED(hr)) {
>> +        errmsg_dialog(hr, "CoCreateInstance(VSSCoordinator) failed");
>> +        goto out;
>> +    }
>> +
>> +    hr = pVssAdmin->RegisterProvider(
>> +        g_gProviderId, CLSID_QGAVSSProvider,
>> +        const_cast<WCHAR*>(QGA_PROVIDER_LNAME), VSS_PROV_SOFTWARE,
>> +        const_cast<WCHAR*>(QGA_PROVIDER_VERSION), g_gProviderVersion);
>> +    if (FAILED(hr)) {
>> +        errmsg_dialog(hr, "RegisterProvider failed");
>> +        goto out;
>> +    }
>> +
>> +out:
>> +    if (pVssAdmin) {
>> +        pVssAdmin->Release();
>> +    }
>> +    CoUninitialize();
>> +
>> +    if (FAILED(hr)) {
>> +        DllUnregisterServer();
>> +    }
>> +
>> +    return hr;
>> +}
>> +
>> +/* Unregister this VSS hardware provider from the system */
>> +STDAPI DllUnregisterServer(void)
>> +{
>> +    TCHAR key[256];
>> +    IVssAdmin *pVssAdmin = NULL;
>> +
>> +    CoInitialize(NULL);
>> +
>> +    HRESULT hr = CoCreateInstance(CLSID_VSSCoordinator,
>> +         NULL, CLSCTX_ALL, IID_IVssAdmin, (void **)&pVssAdmin);
>> +    if (SUCCEEDED(hr)) {
>> +        hr = pVssAdmin->UnregisterProvider(g_gProviderId);
>> +        pVssAdmin->Release();
>> +    } else {
>> +        errmsg_dialog(hr, "CoCreateInstance(VSSCoordinator) failed");
>> +    }
>> +
>> +    sprintf(key, "CLSID\\%s", g_szClsid);
>> +    SHDeleteKey(HKEY_CLASSES_ROOT, key);
>> +    SHDeleteKey(HKEY_CLASSES_ROOT, g_szProgid);
>> +
>> +    CoUninitialize();
>> +
>> +    return S_OK; /* Uninstall should never fail */
>> +}
>> +
>> +
>> +/* Support functions for _bstr_t in MinGW: Originally written by: Diaa Sami 
>> */
>> +
>> +void __stdcall _com_issue_error(HRESULT hr)
>> +{
>> +    printf("_com_issue_error() called with parameter HRESULT = %lu", hr);
>> +}
>> +
>> +namespace _com_util
>> +{
>> +    char * __stdcall ConvertBSTRToString(BSTR bstr)
>> +    {
>> +        const unsigned int stringLength = lstrlenW(bstr);
>> +        char *const ascii = new char [stringLength + 1];
>> +
>> +        wcstombs(ascii, bstr, stringLength + 1);
>> +
>> +        return ascii;
>> +    }
>> +
>> +    BSTR __stdcall ConvertStringToBSTR(const char *const ascii)
>> +    {
>> +        const unsigned int stringLength = lstrlenA(ascii);
>> +        BSTR bstr = SysAllocStringLen(NULL, stringLength);
>> +
>> +        mbstowcs(bstr, ascii, stringLength + 1);
>> +
>> +        return bstr;
>> +    }
>> +}
> 
>> diff --git a/qga/vss-win32-provider/provider.cpp 
>> b/qga/vss-win32-provider/provider.cpp
>> new file mode 100644
>> index 0000000..90a3d25
>> --- /dev/null
>> +++ b/qga/vss-win32-provider/provider.cpp
>> @@ -0,0 +1,479 @@
>> +/*
>> + * QEMU Guest Agent win32 VSS Provider implementations
>> + *
>> + * Copyright Hitachi Data Systems Corp. 2013
>> + *
>> + * Authors:
>> + *  Tomoki Sekiyama   <address@hidden>
>> + *
>> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
>> + * See the COPYING file in the top-level directory.
>> + */
>> +
>> +#include <stdio.h>
>> +#include "../vss-win32.h"
>> +#include "inc/win2003/vscoordint.h"
>> +#include "inc/win2003/vsprov.h"
>> +
>> +static long g_nComObjsInUse;
>> +HINSTANCE g_hinstDll;
>> +
>> +/* VSS common GUID's */
>> +
>> +const CLSID CLSID_VSSCoordinator = { 0xE579AB5F, 0x1CC4, 0x44b4,
>> +    {0xBE, 0xD9, 0xDE, 0x09, 0x91, 0xFF, 0x06, 0x23} };
>> +const IID IID_IVssAdmin = { 0x77ED5996, 0x2F63, 0x11d3,
>> +    {0x8A, 0x39, 0x00, 0xC0, 0x4F, 0x72, 0xD8, 0xE3} };
>> +
>> +const IID IID_IVssHardwareSnapshotProvider = { 0x9593A157, 0x44E9, 0x4344,
>> +    {0xBB, 0xEB, 0x44, 0xFB, 0xF9, 0xB0, 0x6B, 0x10} };
>> +const IID IID_IVssSoftwareSnapshotProvider = { 0x609e123e, 0x2c5a, 0x44d3,
>> +    {0x8f, 0x01, 0x0b, 0x1d, 0x9a, 0x47, 0xd1, 0xff} };
>> +const IID IID_IVssProviderCreateSnapshotSet = { 0x5F894E5B, 0x1E39, 0x4778,
>> +    {0x8E, 0x23, 0x9A, 0xBA, 0xD9, 0xF0, 0xE0, 0x8C} };
>> +const IID IID_IVssProviderNotifications = { 0xE561901F, 0x03A5, 0x4afe,
>> +    {0x86, 0xD0, 0x72, 0xBA, 0xEE, 0xCE, 0x70, 0x04} };
>> +
>> +const IID IID_IVssEnumObject = { 0xAE1C7110, 0x2F60, 0x11d3,
>> +    {0x8A, 0x39, 0x00, 0xC0, 0x4F, 0x72, 0xD8, 0xE3} };
>> +
>> +
>> +void LockModule(BOOL block)
>> +{
>> +    if (block) {
>> +        InterlockedIncrement(&g_nComObjsInUse);
>> +    } else {
>> +        InterlockedDecrement(&g_nComObjsInUse);
>> +    }
>> +}
>> +
>> +/* Empty enumerator for VssObject */
>> +
>> +class CQGAVSSEnumObject : public IVssEnumObject
>> +{
>> +public:
>> +    STDMETHODIMP QueryInterface(REFIID riid, void **ppObj);
>> +    STDMETHODIMP_(ULONG) AddRef();
>> +    STDMETHODIMP_(ULONG) Release();
>> +
>> +    /* IVssEnumObject Methods */
>> +    STDMETHODIMP Next(
>> +        ULONG celt, VSS_OBJECT_PROP *rgelt, ULONG *pceltFetched);
>> +    STDMETHODIMP Skip(ULONG celt);
>> +    STDMETHODIMP Reset(void);
>> +    STDMETHODIMP Clone(IVssEnumObject **ppenum);
>> +
>> +    /* CQGAVSSEnumObject Methods */
>> +    CQGAVSSEnumObject();
>> +    ~CQGAVSSEnumObject();
>> +
>> +private:
>> +    long m_nRefCount;
>> +};
>> +
>> +CQGAVSSEnumObject::CQGAVSSEnumObject()
>> +{
>> +    m_nRefCount = 0;
>> +    LockModule(TRUE);
>> +}
>> +
>> +CQGAVSSEnumObject::~CQGAVSSEnumObject()
>> +{
>> +    LockModule(FALSE);
>> +}
>> +
>> +STDMETHODIMP CQGAVSSEnumObject::QueryInterface(REFIID riid, void **ppObj)
>> +{
>> +    if (riid == IID_IUnknown || riid == IID_IVssEnumObject) {
>> +        *ppObj = static_cast<void*>(static_cast<IVssEnumObject*>(this));
>> +        AddRef();
>> +        return S_OK;
>> +    }
>> +    ppObj = NULL;
>> +    return E_NOINTERFACE;
>> +}
>> +
>> +STDMETHODIMP_(ULONG) CQGAVSSEnumObject::AddRef()
>> +{
>> +    return InterlockedIncrement(&m_nRefCount);
>> +}
>> +
>> +STDMETHODIMP_(ULONG) CQGAVSSEnumObject::Release()
>> +{
>> +    long nRefCount = InterlockedDecrement(&m_nRefCount);
>> +    if (m_nRefCount == 0) {
>> +        delete this;
>> +    }
>> +    return nRefCount;
>> +}
>> +
>> +STDMETHODIMP CQGAVSSEnumObject::Next(
>> +    ULONG celt, VSS_OBJECT_PROP *rgelt, ULONG *pceltFetched)
>> +{
>> +    *pceltFetched = 0;
>> +    return S_FALSE;
>> +}
>> +
>> +STDMETHODIMP CQGAVSSEnumObject::Skip(ULONG celt)
>> +{
>> +    return S_FALSE;
>> +}
>> +
>> +STDMETHODIMP CQGAVSSEnumObject::Reset(void)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVSSEnumObject::Clone(IVssEnumObject **ppenum)
>> +{
>> +    return E_NOTIMPL;
>> +}
>> +
>> +
>> +/* QGAVssProvider */
>> +
>> +class CQGAVssProvider :
>> +    public IVssSoftwareSnapshotProvider,
>> +    public IVssProviderCreateSnapshotSet,
>> +    public IVssProviderNotifications
>> +{
>> +public:
>> +    STDMETHODIMP QueryInterface(REFIID riid, void **ppObj);
>> +    STDMETHODIMP_(ULONG) AddRef();
>> +    STDMETHODIMP_(ULONG) Release();
>> +
>> +    /* IVssSoftwareSnapshotProvider Methods */
>> +    STDMETHODIMP SetContext(LONG lContext);
>> +    STDMETHODIMP GetSnapshotProperties(
>> +        VSS_ID SnapshotId, VSS_SNAPSHOT_PROP *pProp);
>> +    STDMETHODIMP Query(
>> +        VSS_ID QueriedObjectId, VSS_OBJECT_TYPE eQueriedObjectType,
>> +        VSS_OBJECT_TYPE eReturnedObjectsType, IVssEnumObject **ppEnum);
>> +    STDMETHODIMP DeleteSnapshots(
>> +        VSS_ID SourceObjectId, VSS_OBJECT_TYPE eSourceObjectType,
>> +        BOOL bForceDelete, LONG *plDeletedSnapshots,
>> +        VSS_ID *pNondeletedSnapshotID);
>> +    STDMETHODIMP BeginPrepareSnapshot(
>> +        VSS_ID SnapshotSetId, VSS_ID SnapshotId,
>> +        VSS_PWSZ pwszVolumeName, LONG lNewContext);
>> +    STDMETHODIMP IsVolumeSupported(
>> +        VSS_PWSZ pwszVolumeName, BOOL *pbSupportedByThisProvider);
>> +    STDMETHODIMP IsVolumeSnapshotted(
>> +        VSS_PWSZ pwszVolumeName, BOOL *pbSnapshotsPresent,
>> +        LONG *plSnapshotCompatibility);
>> +    STDMETHODIMP SetSnapshotProperty(
>> +        VSS_ID SnapshotId, VSS_SNAPSHOT_PROPERTY_ID eSnapshotPropertyId,
>> +        VARIANT vProperty);
>> +    STDMETHODIMP RevertToSnapshot(VSS_ID SnapshotId);
>> +    STDMETHODIMP QueryRevertStatus(VSS_PWSZ pwszVolume, IVssAsync 
>> **ppAsync);
>> +
>> +    /* IVssProviderCreateSnapshotSet Methods */
>> +    STDMETHODIMP EndPrepareSnapshots(VSS_ID SnapshotSetId);
>> +    STDMETHODIMP PreCommitSnapshots(VSS_ID SnapshotSetId);
>> +    STDMETHODIMP CommitSnapshots(VSS_ID SnapshotSetId);
>> +    STDMETHODIMP PostCommitSnapshots(
>> +        VSS_ID SnapshotSetId, LONG lSnapshotsCount);
>> +    STDMETHODIMP PreFinalCommitSnapshots(VSS_ID SnapshotSetId);
>> +    STDMETHODIMP PostFinalCommitSnapshots(VSS_ID SnapshotSetId);
>> +    STDMETHODIMP AbortSnapshots(VSS_ID SnapshotSetId);
>> +
>> +    /* IVssProviderNotifications Methods */
>> +    STDMETHODIMP OnLoad(IUnknown *pCallback);
>> +    STDMETHODIMP OnUnload(BOOL bForceUnload);
>> +
>> +    /* CQGAVssProvider Methods */
>> +    CQGAVssProvider();
>> +    ~CQGAVssProvider();
>> +
>> +private:
>> +    long m_nRefCount;
>> +};
>> +
>> +CQGAVssProvider::CQGAVssProvider()
>> +{
>> +    m_nRefCount = 0;
>> +    LockModule(TRUE);
>> +}
>> +
>> +CQGAVssProvider::~CQGAVssProvider()
>> +{
>> +    LockModule(FALSE);
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::QueryInterface(REFIID riid, void **ppObj)
>> +{
>> +    if (riid == IID_IUnknown) {
>> +        *ppObj = static_cast<void*>(this);
>> +        AddRef();
>> +        return S_OK;
>> +    } else if (riid == IID_IVssSoftwareSnapshotProvider) {
>> +        *ppObj = static_cast<void*>(
>> +            static_cast<IVssSoftwareSnapshotProvider*>(this));
>> +        AddRef();
>> +        return S_OK;
>> +    } else if (riid == IID_IVssProviderCreateSnapshotSet) {
>> +        *ppObj = static_cast<void*>(
>> +            static_cast<IVssProviderCreateSnapshotSet*>(this));
>> +        AddRef();
>> +        return S_OK;
>> +    } else if (riid == IID_IVssProviderNotifications) {
>> +        *ppObj = static_cast<void*>(
>> +            static_cast<IVssProviderNotifications*>(this));
>> +        AddRef();
>> +        return S_OK;
>> +    }
>> +    *ppObj = NULL;
>> +    return E_NOINTERFACE;
>> +}
>> +
>> +STDMETHODIMP_(ULONG) CQGAVssProvider::AddRef()
>> +{
>> +    return InterlockedIncrement(&m_nRefCount);
>> +}
>> +
>> +STDMETHODIMP_(ULONG) CQGAVssProvider::Release()
>> +{
>> +    long nRefCount = InterlockedDecrement(&m_nRefCount);
>> +    if (m_nRefCount == 0) {
>> +        delete this;
>> +    }
>> +    return nRefCount;
>> +}
>> +
>> +
>> +/*
>> + * IVssSoftwareSnapshotProvider methods
>> + */
>> +
>> +STDMETHODIMP CQGAVssProvider::SetContext(LONG lContext)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::GetSnapshotProperties(
>> +    VSS_ID SnapshotId, VSS_SNAPSHOT_PROP *pProp)
>> +{
>> +    return VSS_E_OBJECT_NOT_FOUND;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::Query(
>> +    VSS_ID QueriedObjectId, VSS_OBJECT_TYPE eQueriedObjectType,
>> +    VSS_OBJECT_TYPE eReturnedObjectsType, IVssEnumObject **ppEnum)
>> +{
>> +    *ppEnum = new CQGAVSSEnumObject;
>> +    (*ppEnum)->AddRef();
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::DeleteSnapshots(
>> +    VSS_ID SourceObjectId, VSS_OBJECT_TYPE eSourceObjectType,
>> +    BOOL bForceDelete, LONG *plDeletedSnapshots, VSS_ID 
>> *pNondeletedSnapshotID)
>> +{
>> +    return E_NOTIMPL;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::BeginPrepareSnapshot(
>> +    VSS_ID SnapshotSetId, VSS_ID SnapshotId,
>> +    VSS_PWSZ pwszVolumeName, LONG lNewContext)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::IsVolumeSupported(
>> +    VSS_PWSZ pwszVolumeName, BOOL *pbSupportedByThisProvider)
>> +{
>> +    *pbSupportedByThisProvider = TRUE;
>> +
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::IsVolumeSnapshotted(VSS_PWSZ pwszVolumeName,
>> +    BOOL *pbSnapshotsPresent, LONG *plSnapshotCompatibility)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::SetSnapshotProperty(VSS_ID SnapshotId,
>> +    VSS_SNAPSHOT_PROPERTY_ID eSnapshotPropertyId, VARIANT vProperty)
>> +{
>> +    return E_NOTIMPL;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::RevertToSnapshot(VSS_ID SnapshotId)
>> +{
>> +    return E_NOTIMPL;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::QueryRevertStatus(
>> +    VSS_PWSZ pwszVolume, IVssAsync **ppAsync)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +
>> +/*
>> + * IVssProviderCreateSnapshotSet methods
>> + */
>> +
>> +STDMETHODIMP CQGAVssProvider::EndPrepareSnapshots(VSS_ID SnapshotSetId)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::PreCommitSnapshots(VSS_ID SnapshotSetId)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::CommitSnapshots(VSS_ID SnapshotSetId)
>> +{
>> +    HRESULT hr = S_OK;
>> +    HANDLE hEvent, hEvent2;
>> +
>> +    hEvent = OpenEvent(EVENT_ALL_ACCESS, FALSE, EVENT_NAME_FROZEN);
>> +    if (hEvent == INVALID_HANDLE_VALUE) {
>> +        hr = E_FAIL;
>> +        goto out;
>> +    }
>> +
>> +    hEvent2 = OpenEvent(EVENT_ALL_ACCESS, FALSE, EVENT_NAME_THAW);
>> +    if (hEvent == INVALID_HANDLE_VALUE) {
>> +        CloseHandle(hEvent);
>> +        hr = E_FAIL;
>> +        goto out;
>> +    }
>> +
>> +    SetEvent(hEvent);
>> +    if (WaitForSingleObject(hEvent2, 60*1000) != WAIT_OBJECT_0) {
>> +        hr = E_ABORT;
>> +    }
>> +
>> +    CloseHandle(hEvent2);
>> +    CloseHandle(hEvent);
>> +out:
>> +    return hr;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::PostCommitSnapshots(
>> +    VSS_ID SnapshotSetId, LONG lSnapshotsCount)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::PreFinalCommitSnapshots(VSS_ID SnapshotSetId)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::PostFinalCommitSnapshots(VSS_ID SnapshotSetId)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::AbortSnapshots(VSS_ID SnapshotSetId)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +/*
>> + * IVssProviderNotifications methods
>> + */
>> +
>> +STDMETHODIMP CQGAVssProvider::OnLoad(IUnknown *pCallback)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProvider::OnUnload(BOOL bForceUnload)
>> +{
>> +    return S_OK;
>> +}
>> +
>> +
>> +/*
>> + * CQGAVssProviderFactory class
>> + */
>> +
>> +class CQGAVssProviderFactory : public IClassFactory
>> +{
>> +public:
>> +    STDMETHODIMP QueryInterface(REFIID riid, void **ppv);
>> +    STDMETHODIMP_(ULONG) AddRef();
>> +    STDMETHODIMP_(ULONG) Release();
>> +    STDMETHODIMP CreateInstance(
>> +        IUnknown *pUnknownOuter, REFIID iid, void **ppv);
>> +    STDMETHODIMP LockServer(BOOL bLock) { return E_NOTIMPL; }
>> +private:
>> +    long m_nRefCount;
>> +};
>> +
>> +STDMETHODIMP CQGAVssProviderFactory::QueryInterface(REFIID riid, void **ppv)
>> +{
>> +    if (riid == IID_IUnknown || riid == IID_IClassFactory) {
>> +        *ppv = static_cast<void*>(this);
>> +        AddRef();
>> +        return S_OK;
>> +    }
>> +    *ppv = NULL;
>> +    return E_NOINTERFACE;
>> +}
>> +
>> +STDMETHODIMP_(ULONG) CQGAVssProviderFactory::AddRef()
>> +{
>> +    LockModule(TRUE);
>> +    return 2;
>> +}
>> +
>> +STDMETHODIMP_(ULONG) CQGAVssProviderFactory::Release()
>> +{
>> +    LockModule(FALSE);
>> +    return 1;
>> +}
>> +
>> +STDMETHODIMP CQGAVssProviderFactory::CreateInstance(
>> +    IUnknown *pUnknownOuter, REFIID iid, void **ppv)
>> +{
>> +    if (pUnknownOuter) {
>> +        return CLASS_E_NOAGGREGATION;
>> +    }
>> +    CQGAVssProvider *pObj = new CQGAVssProvider;
>> +    if (!pObj) {
>> +        return E_OUTOFMEMORY;
>> +    }
>> +    return pObj->QueryInterface(iid, ppv);
>> +}
>> +
>> +
>> +/*
>> + * DLL functions
>> + */
>> +
>> +STDAPI DllGetClassObject(REFCLSID rclsid, REFIID riid, LPVOID *ppv)
>> +{
>> +    static CQGAVssProviderFactory factory;
>> +
>> +    *ppv = NULL;
>> +    if (IsEqualCLSID(rclsid, CLSID_QGAVSSProvider)) {
>> +        return factory.QueryInterface(riid, ppv);
>> +    }
>> +    return CLASS_E_CLASSNOTAVAILABLE;
>> +}
>> +
>> +STDAPI DllCanUnloadNow()
>> +{
>> +    return g_nComObjsInUse == 0 ? S_OK : S_FALSE;
>> +}
>> +
>> +EXTERN_C
>> +BOOL WINAPI DllMain(HINSTANCE hinstDll, DWORD dwReason, LPVOID lpReserved)
>> +{
>> +    switch (dwReason) {
>> +
>> +    case DLL_PROCESS_ATTACH:
>> +        g_hinstDll = hinstDll;
>> +        DisableThreadLibraryCalls(hinstDll);
>> +        break;
>> +    }
>> +
>> +    return TRUE;
>> +}
>