From: Marc-André Lureau <[email protected]> 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 (minimal) properties, and return VSS_E_OBJECT_NOT_FOUND for anything else. 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: [email protected] 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 <[email protected]> --- qga/vss-win32/install.cpp | 1 + qga/vss-win32/provider.cpp | 153 +++++++++++++++++++++++++++++++++++- qga/vss-win32/requester.cpp | 26 ++++++ 3 files changed, 179 insertions(+), 1 deletion(-) diff --git a/qga/vss-win32/install.cpp b/qga/vss-win32/install.cpp index 09d94edd4f53..3b58dc840520 100644 --- a/qga/vss-win32/install.cpp +++ b/qga/vss-win32/install.cpp @@ -331,6 +331,7 @@ 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 1c8eb236e57f..ad2f3ee763e6 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 +143,123 @@ STDMETHODIMP CQGAVSSEnumObject::Clone(IVssEnumObject **ppenum) return E_NOTIMPL; } +/* 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; + }; + + 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 }); + 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; + + 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; + size_t len = (e.volume_name.size() + 1) * sizeof(WCHAR); + VSS_PWSZ volume = (VSS_PWSZ)CoTaskMemAlloc(len); + + if (!volume) { + hr = E_OUTOFMEMORY; + goto out; + } + memcpy(volume, e.volume_name.c_str(), len); + + /* not a real snapshot: no device object, exposure or timestamp */ + 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_pwszOriginalVolumeName = volume; + prop->m_ProviderId = g_gProviderId; + prop->m_lSnapshotAttributes = e.context; + prop->m_eStatus = VSS_SS_CREATED; + } + +out: + 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 +388,7 @@ 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 +408,27 @@ 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 +438,13 @@ 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 +561,7 @@ 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 1b0155c691ef..565eefcfb283 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(); } -- 2.56.0.116.g6de20f6092dc
