qga: vss-win32: Fix interference with snapshot creation by other VSS requesters
When a VSS requester such as vshadow.exe or diskshadow.exe requests to
create disk snapshots, Windows may choose qemu-ga VSS provider if it is
only provider registered on the system. However, because it provides only a
function to freeze the filesystem, the snapshotting fails.
This patch adds a check into CQGAVssProvider::IsVolumeSupported() to reject
the request from other VSS requesters, so that the other provider is chosen.
The check of requester is done by confirming event channels between
qemu-ga's requester and provider established. To ensure that the events are
initialized when CQGAVssProvider::IsVolumeSupported() is called, it moves
the initialization earlier.
Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama@hds.com>
Reviewed-by: Gal Hammer <ghammer@redhat.com>
Reviewed-by: Yan Vugenfirer <yvugenfi@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
diff --git a/qga/vss-win32/provider.cpp b/qga/vss-win32/provider.cpp
index c3030d8..b233646 100644
--- a/qga/vss-win32/provider.cpp
+++ b/qga/vss-win32/provider.cpp
@@ -291,8 +291,17 @@
STDMETHODIMP CQGAVssProvider::IsVolumeSupported(
VSS_PWSZ pwszVolumeName, BOOL *pbSupportedByThisProvider)
{
- *pbSupportedByThisProvider = TRUE;
+ HANDLE hEventFrozen;
+ /* Check if a requester is qemu-ga by whether an event is created */
+ hEventFrozen = OpenEvent(EVENT_ALL_ACCESS, FALSE, EVENT_NAME_FROZEN);
+ if (!hEventFrozen) {
+ *pbSupportedByThisProvider = FALSE;
+ return S_OK;
+ }
+ CloseHandle(hEventFrozen);
+
+ *pbSupportedByThisProvider = TRUE;
return S_OK;
}
