Commit e8953bf0be for qemu.org
commit e8953bf0be6f4399d1333f92db41e4d146f754af
Author: Marc-André Lureau <marcandre.lureau@redhat.com>
Date: Tue Oct 27 20:06:07 2026 +0400
qga/vss: fix provider handling of snapshots
Since commit 374f4676788c, the provider's GetSnapshotProperties()
returns S_OK for any snapshot ID without filling in the properties. VSS
consults every registered provider when a requester looks up a snapshot,
so lookups of snapshots owned by other providers now succeed with an
all-zero VSS_SNAPSHOT_PROP. Backup software relying on it fails, e.g.
Veeam: "Original volume name is not specified for the shadow (shadow
volume id: '{00000000-0000-0000-0000-000000000000}')".
Simply reverting is not an option: 374f4676788c switched to S_OK because
returning VSS_E_OBJECT_NOT_FOUND unconditionally broke qemu-ga's own
snapshot sets. The provider must answer for its own snapshots only. It
does not create real shadow copies, but it does take part in the
snapshot set during qemu-ga fsfreeze cycles. Remember the snapshot IDs
received in BeginPrepareSnapshot(), return their required properties,
and return VSS_E_OBJECT_NOT_FOUND for anything else. Fill every required
VSS_SNAPSHOT_PROP member except the exposed name and path, which are
optional. The snapshot device object is an empty string because the
host-side snapshot has no guest-visible device.
Entries are dropped when VSS deletes the snapshots or the set, or when
the set is aborted (AbortSnapshots()).
COM+ may hand out several CQGAVssProvider instances (and serve several
client processes), so this registry is module-global. It is per-process
by design and safe because the COM+ application is hosted by a single NT
service (see CreateServiceForApplication() in install.cpp): COM+ forbids
pooling and recycling for service-hosted applications, so exactly one
surrogate process ever hosts the provider.
On the requester side, the snapshot set is created in the persistent
VSS_CTX_APP_ROLLBACK context, so VSS keeps it after the freeze/thaw
cycle and may keep querying providers about it. The provider registry
does not outlive the cycle (requester_thaw() stops the hosting service,
and the provider process with it), so later queries would get "not
found" for a set VSS still believes exists. Make requester_thaw() delete
the snapshot set explicitly at the end of the cycle, whatever its
outcome (including BackupComplete() failure and aborted snapshot sets).
A failure to delete is only logged, since the guest filesystems have
already been thawed.
Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4584
Buglink: https://redhat.atlassian.net/browse/RHEL-250662
Fixes: 374f4676788c ("qga: Fix VSS provider GetSnapshotProperties return value")
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20261027160606.2668607-2-marcandre.lureau@redhat.com
Reviewed-by: Kostiantyn Kostiuk <kkostiuk@redhat.com>
Signed-off-by: Kostiantyn Kostiuk <kkostiuk@redhat.com>
diff --git a/qga/vss-win32/install.cpp b/qga/vss-win32/install.cpp
index 431fcd1cbe..df00588c92 100644
--- a/qga/vss-win32/install.cpp
+++ b/qga/vss-win32/install.cpp
@@ -422,6 +422,7 @@ STDAPI COMRegister(void)
chk(put_Value(pObj, L"Authentication", short(6)));
chk(put_Value(pObj, L"AuthenticationCapability", short(2)));
chk(put_Value(pObj, L"ImpersonationLevel", short(2)));
+ /* NT-service-hosted apps have ConcurrentApps=1 enforced */
chk(pApps->SaveChanges(&n));
/* The app should be deleted if something fails after SaveChanges */
diff --git a/qga/vss-win32/provider.cpp b/qga/vss-win32/provider.cpp
index 1c8eb236e5..bbc30dd57d 100644
--- a/qga/vss-win32/provider.cpp
+++ b/qga/vss-win32/provider.cpp
@@ -11,6 +11,11 @@
*/
#include "qemu/osdep.h"
+
+#include <vector>
+#include <algorithm>
+#include <string>
+
#include "vss-common.h"
#include "vss-debug.h"
#ifdef HAVE_VSS_SDK
@@ -138,6 +143,170 @@ STDMETHODIMP CQGAVSSEnumObject::Clone(IVssEnumObject **ppenum)
return E_NOTIMPL;
}
+static VSS_PWSZ qga_vss_strdup(const WCHAR *value)
+{
+ size_t len = (wcslen(value) + 1) * sizeof(WCHAR);
+ VSS_PWSZ str = (VSS_PWSZ)CoTaskMemAlloc(len);
+
+ if (str) {
+ memcpy(str, value, len);
+ }
+ return str;
+}
+
+static VSS_PWSZ qga_vss_strdup(const std::wstring &value)
+{
+ return qga_vss_strdup(value.c_str());
+}
+
+static VSS_TIMESTAMP qga_vss_timestamp(void)
+{
+ FILETIME ft;
+ ULARGE_INTEGER value;
+
+ GetSystemTimeAsFileTime(&ft);
+ value.LowPart = ft.dwLowDateTime;
+ value.HighPart = ft.dwHighDateTime;
+ return value.QuadPart;
+}
+
+/* Registry of the snapshot IDs for this provider */
+class QGAVssSnapshotRegistry
+{
+public:
+ bool Track(VSS_ID set_id, VSS_ID snapshot_id,
+ VSS_PWSZ volume_name, LONG context);
+ HRESULT GetProperties(VSS_ID snapshot_id, VSS_SNAPSHOT_PROP *prop) const;
+ LONG RemoveSet(VSS_ID set_id); /* returns how many were removed */
+ bool Remove(VSS_ID snapshot_id);
+
+private:
+ struct Entry {
+ VSS_ID set_id;
+ VSS_ID snapshot_id;
+ std::wstring volume_name;
+ LONG context;
+ VSS_TIMESTAMP timestamp;
+ };
+
+ std::vector<Entry> m_entries;
+ mutable SRWLOCK m_lock = SRWLOCK_INIT;
+};
+
+static QGAVssSnapshotRegistry qga_vss_registry;
+
+bool QGAVssSnapshotRegistry::Track(VSS_ID set_id, VSS_ID snapshot_id,
+ VSS_PWSZ volume_name, LONG context)
+{
+ bool ok;
+
+ AcquireSRWLockExclusive(&m_lock);
+ try {
+ m_entries.push_back(Entry { set_id, snapshot_id, volume_name,
+ context, qga_vss_timestamp() });
+ ok = true;
+ } catch (...) {
+ ok = false;
+ }
+ ReleaseSRWLockExclusive(&m_lock);
+ return ok;
+}
+
+HRESULT QGAVssSnapshotRegistry::GetProperties(VSS_ID snapshot_id,
+ VSS_SNAPSHOT_PROP *prop) const
+{
+ HRESULT hr = S_OK;
+ VSS_PWSZ device = NULL, original = NULL;
+ VSS_PWSZ originating = NULL, service = NULL;
+
+ AcquireSRWLockShared(&m_lock);
+ auto it = std::find_if(m_entries.begin(), m_entries.end(),
+ [&](const Entry &e) {
+ return IsEqualGUID(e.snapshot_id, snapshot_id);
+ });
+ if (it == m_entries.end()) {
+ hr = VSS_E_OBJECT_NOT_FOUND;
+ goto out;
+ }
+
+ {
+ const Entry &e = *it;
+ WCHAR machine[256] = L"";
+ DWORD machine_size = ARRAYSIZE(machine);
+
+ if (!GetComputerNameExW(ComputerNameDnsFullyQualified, machine,
+ &machine_size)) {
+ *machine = L'\0';
+ }
+
+ device = qga_vss_strdup(L"");
+ original = qga_vss_strdup(e.volume_name);
+ originating = qga_vss_strdup(machine);
+ service = qga_vss_strdup(machine);
+ if (!device || !original || !originating || !service) {
+ hr = E_OUTOFMEMORY;
+ goto out;
+ }
+
+ memset(prop, 0, sizeof(*prop));
+ prop->m_SnapshotId = e.snapshot_id;
+ prop->m_SnapshotSetId = e.set_id;
+ prop->m_lSnapshotsCount = std::count_if(m_entries.begin(),
+ m_entries.end(), [&](const Entry &o) {
+ return IsEqualGUID(o.set_id, e.set_id);
+ });
+ prop->m_pwszSnapshotDeviceObject = device;
+ prop->m_pwszOriginalVolumeName = original;
+ prop->m_pwszOriginatingMachine = originating;
+ prop->m_pwszServiceMachine = service;
+ prop->m_ProviderId = g_gProviderId;
+ prop->m_lSnapshotAttributes = e.context;
+ prop->m_tsCreationTimestamp = e.timestamp;
+ prop->m_eStatus = VSS_SS_CREATED;
+
+ device = original = originating = service = NULL;
+ }
+
+out:
+ CoTaskMemFree(device);
+ CoTaskMemFree(original);
+ CoTaskMemFree(originating);
+ CoTaskMemFree(service);
+ ReleaseSRWLockShared(&m_lock);
+ return hr;
+}
+
+LONG QGAVssSnapshotRegistry::RemoveSet(VSS_ID set_id)
+{
+ LONG removed;
+
+ AcquireSRWLockExclusive(&m_lock);
+ auto it = std::remove_if(m_entries.begin(), m_entries.end(),
+ [&](const Entry &e) {
+ return IsEqualGUID(e.set_id, set_id);
+ });
+ removed = m_entries.end() - it;
+ m_entries.erase(it, m_entries.end());
+ ReleaseSRWLockExclusive(&m_lock);
+ return removed;
+}
+
+bool QGAVssSnapshotRegistry::Remove(VSS_ID snapshot_id)
+{
+ bool found;
+
+ AcquireSRWLockExclusive(&m_lock);
+ auto it = std::find_if(m_entries.begin(), m_entries.end(),
+ [&](const Entry &e) {
+ return IsEqualGUID(e.snapshot_id, snapshot_id);
+ });
+ found = it != m_entries.end();
+ if (found) {
+ m_entries.erase(it);
+ }
+ ReleaseSRWLockExclusive(&m_lock);
+ return found;
+}
/* QGAVssProvider */
@@ -266,7 +435,7 @@ STDMETHODIMP CQGAVssProvider::SetContext(LONG lContext)
STDMETHODIMP CQGAVssProvider::GetSnapshotProperties(
VSS_ID SnapshotId, VSS_SNAPSHOT_PROP *pProp)
{
- return S_OK;
+ return qga_vss_registry.GetProperties(SnapshotId, pProp);
}
STDMETHODIMP CQGAVssProvider::Query(
@@ -286,6 +455,27 @@ STDMETHODIMP CQGAVssProvider::DeleteSnapshots(
VSS_ID SourceObjectId, VSS_OBJECT_TYPE eSourceObjectType,
BOOL bForceDelete, LONG *plDeletedSnapshots, VSS_ID *pNondeletedSnapshotID)
{
+ LONG deleted = 0;
+
+ switch (eSourceObjectType) {
+ case VSS_OBJECT_SNAPSHOT:
+ if (qga_vss_registry.Remove(SourceObjectId)) {
+ deleted = 1;
+ }
+ break;
+ case VSS_OBJECT_SNAPSHOT_SET:
+ deleted = qga_vss_registry.RemoveSet(SourceObjectId);
+ break;
+ default:
+ break;
+ }
+
+ if (deleted > 0) {
+ *plDeletedSnapshots = deleted;
+ *pNondeletedSnapshotID = GUID_NULL;
+ return S_OK;
+ }
+
*plDeletedSnapshots = 0;
*pNondeletedSnapshotID = SourceObjectId;
return S_OK;
@@ -295,6 +485,13 @@ STDMETHODIMP CQGAVssProvider::BeginPrepareSnapshot(
VSS_ID SnapshotSetId, VSS_ID SnapshotId,
VSS_PWSZ pwszVolumeName, LONG lNewContext)
{
+ if (!pwszVolumeName) {
+ return E_INVALIDARG;
+ }
+ if (!qga_vss_registry.Track(SnapshotSetId, SnapshotId,
+ pwszVolumeName, lNewContext)) {
+ return E_OUTOFMEMORY;
+ }
return S_OK;
}
@@ -411,6 +608,7 @@ STDMETHODIMP CQGAVssProvider::PostFinalCommitSnapshots(VSS_ID SnapshotSetId)
STDMETHODIMP CQGAVssProvider::AbortSnapshots(VSS_ID SnapshotSetId)
{
+ qga_vss_registry.RemoveSet(SnapshotSetId);
return S_OK;
}
diff --git a/qga/vss-win32/requester.cpp b/qga/vss-win32/requester.cpp
index 1b0155c691..565eefcfb2 100644
--- a/qga/vss-win32/requester.cpp
+++ b/qga/vss-win32/requester.cpp
@@ -52,6 +52,7 @@ static t_VssFreeSnapshotProperties pVssFreeSnapshotProperties;
static struct QGAVSSContext {
IVssBackupComponents *pVssbc; /* VSS requester interface */
IVssAsync *pAsyncSnapshot; /* async info of VSS snapshot operation */
+ VSS_ID idSnapshotSet; /* snapshot set created for this cycle */
HANDLE hEventFrozen; /* notify fs/writer freeze from provider */
HANDLE hEventThaw; /* request provider to thaw */
HANDLE hEventTimeout; /* notify timeout in provider */
@@ -116,6 +117,7 @@ static void requester_cleanup(void)
vss_ctx.pVssbc->Release();
vss_ctx.pVssbc = NULL;
}
+ vss_ctx.idSnapshotSet = GUID_NULL;
vss_ctx.cFrozenVols = 0;
qga_debug_end;
}
@@ -446,6 +448,7 @@ void requester_freeze(int *num_vols, void *mountpoints, ErrorSet *errset)
err_set(errset, hr, "failed to start snapshot set");
goto out;
}
+ vss_ctx.idSnapshotSet = guidSnapshotSet;
if (mountpoints) {
PWCHAR volume_name_wchar;
@@ -680,6 +683,29 @@ void requester_thaw(int *num_vols, void *mountpints, ErrorSet *errset)
err_set(errset, hr, "failed to do snapshot set");
}
+ /*
+ * The snapshot set is created in VSS_CTX_APP_ROLLBACK context, so
+ * it is persistent: if it was committed, VSS keeps it (and keeps
+ * querying providers about it) until it is explicitly deleted. The
+ * freeze/thaw cycle is over whatever the outcome above, so delete
+ * it now. Failure is not fatal here, only log it.
+ */
+ {
+ LONG lDeletedSnapshots = 0;
+ VSS_ID idNonDeletedSnapshot;
+ HRESULT hrDelete;
+
+ hrDelete = vss_ctx.pVssbc->DeleteSnapshots(vss_ctx.idSnapshotSet,
+ VSS_OBJECT_SNAPSHOT_SET,
+ TRUE,
+ &lDeletedSnapshots,
+ &idNonDeletedSnapshot);
+ if (FAILED(hrDelete)) {
+ qga_debug("failed to delete snapshot set after thaw,"
+ " hr=0x%08lx", hrDelete);
+ }
+ }
+
if (err_is_set(errset)) {
vss_ctx.pVssbc->AbortBackup();
}