qemu-ga: Add Windows VSS provider and requester as DLL

Adds VSS provider and requester as a qga-vss.dll, which is loaded by
Windows VSS service as well as by qemu-ga.

"provider.cpp" implements a basic stub of a software VSS provider.
Currently, this module only relays a frozen event from VSS service to the
agent, and thaw event from the agent to VSS service, to block VSS process
to keep the system frozen while snapshots are taken at the host.

To register the provider to the guest system as COM+ application, the type
library (.tlb) for qga-vss.dll is required. To build it from COM IDL (.idl),
VisualC++, MIDL and stdole2.tlb in Windows SDK are required. This patch also
adds pre-compiled .tlb file in the repository in order to enable
cross-compile qemu-ga.exe for Windows with VSS support.

"requester.cpp" provides the VSS requester to kick the VSS snapshot process.
Qemu-ga.exe works without the DLL, although fsfreeze features are disabled.

These functions are only supported in Windows 2003 or later. In older
systems, fsfreeze features are disabled.

In several versions of Windows which don't support attribute
VSS_VOLSNAP_ATTR_NO_AUTORECOVERY, DoSnapshotSet fails with error
VSS_E_OBJECT_NOT_FOUND. In this patch, we just ignore this error.
To solve this fundamentally, we need a framework to handle mount writable
snapshot on guests, which is required by VSS auto-recovery feature
(cleanup phase after a snapshot is taken).

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama@hds.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

1 files changed, 507 insertions, 0 deletions

diff --git a/qga/vss-win32/requester.cpp b/qga/vss-win32/requester.cpp
new file mode 100644
index 0000000000..1e8dd3dfa8
--- /dev/null
+++ b/qga/vss-win32/requester.cpp
@@ -0,0 +1,507 @@
+/*
+ * QEMU Guest Agent win32 VSS Requester implementations
+ *
+ * Copyright Hitachi Data Systems Corp. 2013
+ *
+ * Authors:
+ *  Tomoki Sekiyama   <tomoki.sekiyama@hds.com>
+ *
+ * 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-common.h"
+#include "requester.h"
+#include "assert.h"
+#include "inc/win2003/vswriter.h"
+#include "inc/win2003/vsbackup.h"
+
+/* Max wait time for frozen event (VSS can only hold writes for 10 seconds) */
+#define VSS_TIMEOUT_FREEZE_MSEC 10000
+
+/* Call QueryStatus every 10 ms while waiting for frozen event */
+#define VSS_TIMEOUT_EVENT_MSEC 10
+
+#define err_set(e, err, fmt, ...) \
+    ((e)->error_set((e)->errp, err, (e)->err_class, fmt, ## __VA_ARGS__))
+#define err_is_set(e) ((e)->errp && *(e)->errp)
+
+
+/* Handle to VSSAPI.DLL */
+static HMODULE hLib;
+
+/* Functions in VSSAPI.DLL */
+typedef HRESULT(STDAPICALLTYPE * t_CreateVssBackupComponents)(
+    OUT IVssBackupComponents**);
+typedef void(APIENTRY * t_VssFreeSnapshotProperties)(IN VSS_SNAPSHOT_PROP*);
+static t_CreateVssBackupComponents pCreateVssBackupComponents;
+static t_VssFreeSnapshotProperties pVssFreeSnapshotProperties;
+
+/* Variables used while applications and filesystes are frozen by VSS */
+static struct QGAVSSContext {
+    IVssBackupComponents *pVssbc;  /* VSS requester interface */
+    IVssAsync *pAsyncSnapshot;     /* async info of VSS snapshot operation */
+    HANDLE hEventFrozen;           /* notify fs/writer freeze from provider */
+    HANDLE hEventThaw;             /* request provider to thaw */
+    HANDLE hEventTimeout;          /* notify timeout in provider */
+    int cFrozenVols;               /* number of frozen volumes */
+} vss_ctx;
+
+STDAPI requester_init(void)
+{
+    vss_ctx.hEventFrozen =  INVALID_HANDLE_VALUE;
+    vss_ctx.hEventThaw = INVALID_HANDLE_VALUE;
+    vss_ctx.hEventTimeout = INVALID_HANDLE_VALUE;
+
+    COMInitializer initializer; /* to call CoInitializeSecurity */
+    HRESULT hr = CoInitializeSecurity(
+        NULL, -1, NULL, NULL, RPC_C_AUTHN_LEVEL_PKT_PRIVACY,
+        RPC_C_IMP_LEVEL_IDENTIFY, NULL, EOAC_NONE, NULL);
+    if (FAILED(hr)) {
+        fprintf(stderr, "failed to CoInitializeSecurity (error %lx)\n", hr);
+        return hr;
+    }
+
+    hLib = LoadLibraryA("VSSAPI.DLL");
+    if (!hLib) {
+        fprintf(stderr, "failed to load VSSAPI.DLL\n");
+        return HRESULT_FROM_WIN32(GetLastError());
+    }
+
+    pCreateVssBackupComponents = (t_CreateVssBackupComponents)
+        GetProcAddress(hLib,
+#ifdef _WIN64 /* 64bit environment */
+        "?CreateVssBackupComponents@@YAJPEAPEAVIVssBackupComponents@@@Z"
+#else /* 32bit environment */
+        "?CreateVssBackupComponents@@YGJPAPAVIVssBackupComponents@@@Z"
+#endif
+        );
+    if (!pCreateVssBackupComponents) {
+        fprintf(stderr, "failed to get proc address from VSSAPI.DLL\n");
+        return HRESULT_FROM_WIN32(GetLastError());
+    }
+
+    pVssFreeSnapshotProperties = (t_VssFreeSnapshotProperties)
+        GetProcAddress(hLib, "VssFreeSnapshotProperties");
+    if (!pVssFreeSnapshotProperties) {
+        fprintf(stderr, "failed to get proc address from VSSAPI.DLL\n");
+        return HRESULT_FROM_WIN32(GetLastError());
+    }
+
+    return S_OK;
+}
+
+static void requester_cleanup(void)
+{
+    if (vss_ctx.hEventFrozen != INVALID_HANDLE_VALUE) {
+        CloseHandle(vss_ctx.hEventFrozen);
+        vss_ctx.hEventFrozen = INVALID_HANDLE_VALUE;
+    }
+    if (vss_ctx.hEventThaw != INVALID_HANDLE_VALUE) {
+        CloseHandle(vss_ctx.hEventThaw);
+        vss_ctx.hEventThaw = INVALID_HANDLE_VALUE;
+    }
+    if (vss_ctx.hEventTimeout != INVALID_HANDLE_VALUE) {
+        CloseHandle(vss_ctx.hEventTimeout);
+        vss_ctx.hEventTimeout = INVALID_HANDLE_VALUE;
+    }
+    if (vss_ctx.pAsyncSnapshot) {
+        vss_ctx.pAsyncSnapshot->Release();
+        vss_ctx.pAsyncSnapshot = NULL;
+    }
+    if (vss_ctx.pVssbc) {
+        vss_ctx.pVssbc->Release();
+        vss_ctx.pVssbc = NULL;
+    }
+    vss_ctx.cFrozenVols = 0;
+}
+
+STDAPI requester_deinit(void)
+{
+    requester_cleanup();
+
+    pCreateVssBackupComponents = NULL;
+    pVssFreeSnapshotProperties = NULL;
+    if (hLib) {
+        FreeLibrary(hLib);
+        hLib = NULL;
+    }
+
+    return S_OK;
+}
+
+static HRESULT WaitForAsync(IVssAsync *pAsync)
+{
+    HRESULT ret, hr;
+
+    do {
+        hr = pAsync->Wait();
+        if (FAILED(hr)) {
+            ret = hr;
+            break;
+        }
+        hr = pAsync->QueryStatus(&ret, NULL);
+        if (FAILED(hr)) {
+            ret = hr;
+            break;
+        }
+    } while (ret == VSS_S_ASYNC_PENDING);
+
+    return ret;
+}
+
+static void AddComponents(ErrorSet *errset)
+{
+    unsigned int cWriters, i;
+    VSS_ID id, idInstance, idWriter;
+    BSTR bstrWriterName = NULL;
+    VSS_USAGE_TYPE usage;
+    VSS_SOURCE_TYPE source;
+    unsigned int cComponents, c1, c2, j;
+    COMPointer<IVssExamineWriterMetadata> pMetadata;
+    COMPointer<IVssWMComponent> pComponent;
+    PVSSCOMPONENTINFO info;
+    HRESULT hr;
+
+    hr = vss_ctx.pVssbc->GetWriterMetadataCount(&cWriters);
+    if (FAILED(hr)) {
+        err_set(errset, hr, "failed to get writer metadata count");
+        goto out;
+    }
+
+    for (i = 0; i < cWriters; i++) {
+        hr = vss_ctx.pVssbc->GetWriterMetadata(i, &id, pMetadata.replace());
+        if (FAILED(hr)) {
+            err_set(errset, hr, "failed to get writer metadata of %d/%d",
+                             i, cWriters);
+            goto out;
+        }
+
+        hr = pMetadata->GetIdentity(&idInstance, &idWriter,
+                                    &bstrWriterName, &usage, &source);
+        if (FAILED(hr)) {
+            err_set(errset, hr, "failed to get identity of writer %d/%d",
+                             i, cWriters);
+            goto out;
+        }
+
+        hr = pMetadata->GetFileCounts(&c1, &c2, &cComponents);
+        if (FAILED(hr)) {
+            err_set(errset, hr, "failed to get file counts of %S",
+                             bstrWriterName);
+            goto out;
+        }
+
+        for (j = 0; j < cComponents; j++) {
+            hr = pMetadata->GetComponent(j, pComponent.replace());
+            if (FAILED(hr)) {
+                err_set(errset, hr,
+                                 "failed to get component %d/%d of %S",
+                                 j, cComponents, bstrWriterName);
+                goto out;
+            }
+
+            hr = pComponent->GetComponentInfo(&info);
+            if (FAILED(hr)) {
+                err_set(errset, hr,
+                                 "failed to get component info %d/%d of %S",
+                                 j, cComponents, bstrWriterName);
+                goto out;
+            }
+
+            if (info->bSelectable) {
+                hr = vss_ctx.pVssbc->AddComponent(idInstance, idWriter,
+                                                  info->type,
+                                                  info->bstrLogicalPath,
+                                                  info->bstrComponentName);
+                if (FAILED(hr)) {
+                    err_set(errset, hr, "failed to add component %S(%S)",
+                                     info->bstrComponentName, bstrWriterName);
+                    goto out;
+                }
+            }
+            SysFreeString(bstrWriterName);
+            bstrWriterName = NULL;
+            pComponent->FreeComponentInfo(info);
+            info = NULL;
+        }
+    }
+out:
+    if (bstrWriterName) {
+        SysFreeString(bstrWriterName);
+    }
+    if (pComponent && info) {
+        pComponent->FreeComponentInfo(info);
+    }
+}
+
+void requester_freeze(int *num_vols, ErrorSet *errset)
+{
+    COMPointer<IVssAsync> pAsync;
+    HANDLE volume;
+    HRESULT hr;
+    LONG ctx;
+    GUID guidSnapshotSet = GUID_NULL;
+    SECURITY_DESCRIPTOR sd;
+    SECURITY_ATTRIBUTES sa;
+    WCHAR short_volume_name[64], *display_name = short_volume_name;
+    DWORD wait_status;
+    int num_fixed_drives = 0, i;
+
+    if (vss_ctx.pVssbc) { /* already frozen */
+        *num_vols = 0;
+        return;
+    }
+
+    CoInitialize(NULL);
+
+    assert(pCreateVssBackupComponents != NULL);
+    hr = pCreateVssBackupComponents(&vss_ctx.pVssbc);
+    if (FAILED(hr)) {
+        err_set(errset, hr, "failed to create VSS backup components");
+        goto out;
+    }
+
+    hr = vss_ctx.pVssbc->InitializeForBackup();
+    if (FAILED(hr)) {
+        err_set(errset, hr, "failed to initialize for backup");
+        goto out;
+    }
+
+    hr = vss_ctx.pVssbc->SetBackupState(true, true, VSS_BT_FULL, false);
+    if (FAILED(hr)) {
+        err_set(errset, hr, "failed to set backup state");
+        goto out;
+    }
+
+    /*
+     * Currently writable snapshots are not supported.
+     * To prevent the final commit (which requires to write to snapshots),
+     * ATTR_NO_AUTORECOVERY and ATTR_TRANSPORTABLE are specified here.
+     */
+    ctx = VSS_CTX_APP_ROLLBACK | VSS_VOLSNAP_ATTR_TRANSPORTABLE |
+        VSS_VOLSNAP_ATTR_NO_AUTORECOVERY | VSS_VOLSNAP_ATTR_TXF_RECOVERY;
+    hr = vss_ctx.pVssbc->SetContext(ctx);
+    if (hr == (HRESULT)VSS_E_UNSUPPORTED_CONTEXT) {
+        /* Non-server version of Windows doesn't support ATTR_TRANSPORTABLE */
+        ctx &= ~VSS_VOLSNAP_ATTR_TRANSPORTABLE;
+        hr = vss_ctx.pVssbc->SetContext(ctx);
+    }
+    if (FAILED(hr)) {
+        err_set(errset, hr, "failed to set backup context");
+        goto out;
+    }
+
+    hr = vss_ctx.pVssbc->GatherWriterMetadata(pAsync.replace());
+    if (SUCCEEDED(hr)) {
+        hr = WaitForAsync(pAsync);
+    }
+    if (FAILED(hr)) {
+        err_set(errset, hr, "failed to gather writer metadata");
+        goto out;
+    }
+
+    AddComponents(errset);
+    if (err_is_set(errset)) {
+        goto out;
+    }
+
+    hr = vss_ctx.pVssbc->StartSnapshotSet(&guidSnapshotSet);
+    if (FAILED(hr)) {
+        err_set(errset, hr, "failed to start snapshot set");
+        goto out;
+    }
+
+    volume = FindFirstVolumeW(short_volume_name, sizeof(short_volume_name));
+    if (volume == INVALID_HANDLE_VALUE) {
+        err_set(errset, hr, "failed to find first volume");
+        goto out;
+    }
+    for (;;) {
+        if (GetDriveTypeW(short_volume_name) == DRIVE_FIXED) {
+            VSS_ID pid;
+            hr = vss_ctx.pVssbc->AddToSnapshotSet(short_volume_name,
+                                                  g_gProviderId, &pid);
+            if (FAILED(hr)) {
+                WCHAR volume_path_name[PATH_MAX];
+                if (GetVolumePathNamesForVolumeNameW(
+                        short_volume_name, volume_path_name,
+                        sizeof(volume_path_name), NULL) && *volume_path_name) {
+                    display_name = volume_path_name;
+                }
+                err_set(errset, hr, "failed to add %S to snapshot set",
+                                 display_name);
+                FindVolumeClose(volume);
+                goto out;
+            }
+            num_fixed_drives++;
+        }
+        if (!FindNextVolumeW(volume, short_volume_name,
+                             sizeof(short_volume_name))) {
+            FindVolumeClose(volume);
+            break;
+        }
+    }
+
+    if (num_fixed_drives == 0) {
+        goto out; /* If there is no fixed drive, just exit. */
+    }
+
+    hr = vss_ctx.pVssbc->PrepareForBackup(pAsync.replace());
+    if (SUCCEEDED(hr)) {
+        hr = WaitForAsync(pAsync);
+    }
+    if (FAILED(hr)) {
+        err_set(errset, hr, "failed to prepare for backup");
+        goto out;
+    }
+
+    hr = vss_ctx.pVssbc->GatherWriterStatus(pAsync.replace());
+    if (SUCCEEDED(hr)) {
+        hr = WaitForAsync(pAsync);
+    }
+    if (FAILED(hr)) {
+        err_set(errset, hr, "failed to gather writer status");
+        goto out;
+    }
+
+    /* Allow unrestricted access to events */
+    InitializeSecurityDescriptor(&sd, SECURITY_DESCRIPTOR_REVISION);
+    SetSecurityDescriptorDacl(&sd, TRUE, NULL, FALSE);
+    sa.nLength = sizeof(sa);
+    sa.lpSecurityDescriptor = &sd;
+    sa.bInheritHandle = FALSE;
+
+    vss_ctx.hEventFrozen = CreateEvent(&sa, TRUE, FALSE, EVENT_NAME_FROZEN);
+    if (vss_ctx.hEventFrozen == INVALID_HANDLE_VALUE) {
+        err_set(errset, GetLastError(), "failed to create event %s",
+                EVENT_NAME_FROZEN);
+        goto out;
+    }
+    vss_ctx.hEventThaw = CreateEvent(&sa, TRUE, FALSE, EVENT_NAME_THAW);
+    if (vss_ctx.hEventThaw == INVALID_HANDLE_VALUE) {
+        err_set(errset, GetLastError(), "failed to create event %s",
+                EVENT_NAME_THAW);
+        goto out;
+    }
+    vss_ctx.hEventTimeout = CreateEvent(&sa, TRUE, FALSE, EVENT_NAME_TIMEOUT);
+    if (vss_ctx.hEventTimeout == INVALID_HANDLE_VALUE) {
+        err_set(errset, GetLastError(), "failed to create event %s",
+                EVENT_NAME_TIMEOUT);
+        goto out;
+    }
+
+    /*
+     * Start VSS quiescing operations.
+     * CQGAVssProvider::CommitSnapshots will kick vss_ctx.hEventFrozen
+     * after the applications and filesystems are frozen.
+     */
+    hr = vss_ctx.pVssbc->DoSnapshotSet(&vss_ctx.pAsyncSnapshot);
+    if (FAILED(hr)) {
+        err_set(errset, hr, "failed to do snapshot set");
+        goto out;
+    }
+
+    /* Need to call QueryStatus several times to make VSS provider progress */
+    for (i = 0; i < VSS_TIMEOUT_FREEZE_MSEC/VSS_TIMEOUT_EVENT_MSEC; i++) {
+        HRESULT hr2 = vss_ctx.pAsyncSnapshot->QueryStatus(&hr, NULL);
+        if (FAILED(hr2)) {
+            err_set(errset, hr, "failed to do snapshot set");
+            goto out;
+        }
+        if (hr != VSS_S_ASYNC_PENDING) {
+            err_set(errset, E_FAIL,
+                    "DoSnapshotSet exited without Frozen event");
+            goto out;
+        }
+        wait_status = WaitForSingleObject(vss_ctx.hEventFrozen,
+                                          VSS_TIMEOUT_EVENT_MSEC);
+        if (wait_status != WAIT_TIMEOUT) {
+            break;
+        }
+    }
+    if (wait_status != WAIT_OBJECT_0) {
+        err_set(errset, E_FAIL,
+                "couldn't receive Frozen event from VSS provider");
+        goto out;
+    }
+
+    *num_vols = vss_ctx.cFrozenVols = num_fixed_drives;
+    return;
+
+out:
+    if (vss_ctx.pVssbc) {
+        vss_ctx.pVssbc->AbortBackup();
+    }
+    requester_cleanup();
+    CoUninitialize();
+}
+
+
+void requester_thaw(int *num_vols, ErrorSet *errset)
+{
+    COMPointer<IVssAsync> pAsync;
+
+    if (vss_ctx.hEventThaw == INVALID_HANDLE_VALUE) {
+        /*
+         * In this case, DoSnapshotSet is aborted or not started,
+         * and no volumes must be frozen. We return without an error.
+         */
+        *num_vols = 0;
+        return;
+    }
+
+    /* Tell the provider that the snapshot is finished. */
+    SetEvent(vss_ctx.hEventThaw);
+
+    assert(vss_ctx.pVssbc);
+    assert(vss_ctx.pAsyncSnapshot);
+
+    HRESULT hr = WaitForAsync(vss_ctx.pAsyncSnapshot);
+    switch (hr) {
+    case VSS_S_ASYNC_FINISHED:
+        hr = vss_ctx.pVssbc->BackupComplete(pAsync.replace());
+        if (SUCCEEDED(hr)) {
+            hr = WaitForAsync(pAsync);
+        }
+        if (FAILED(hr)) {
+            err_set(errset, hr, "failed to complete backup");
+        }
+        break;
+
+    case (HRESULT)VSS_E_OBJECT_NOT_FOUND:
+        /*
+         * On Windows earlier than 2008 SP2 which does not support
+         * VSS_VOLSNAP_ATTR_NO_AUTORECOVERY context, the final commit is not
+         * skipped and VSS is aborted by VSS_E_OBJECT_NOT_FOUND. However, as
+         * the system had been frozen until fsfreeze-thaw command was issued,
+         * we ignore this error.
+         */
+        vss_ctx.pVssbc->AbortBackup();
+        break;
+
+    case VSS_E_UNEXPECTED_PROVIDER_ERROR:
+        if (WaitForSingleObject(vss_ctx.hEventTimeout, 0) != WAIT_OBJECT_0) {
+            err_set(errset, hr, "unexpected error in VSS provider");
+            break;
+        }
+        /* fall through if hEventTimeout is signaled */
+
+    case (HRESULT)VSS_E_HOLD_WRITES_TIMEOUT:
+        err_set(errset, hr, "couldn't hold writes: "
+                "fsfreeze is limited up to 10 seconds");
+        break;
+
+    default:
+        err_set(errset, hr, "failed to do snapshot set");
+    }
+
+    if (err_is_set(errset)) {
+        vss_ctx.pVssbc->AbortBackup();
+    }
+    *num_vols = vss_ctx.cFrozenVols;
+    requester_cleanup();
+
+    CoUninitialize();
+}