[PATCH 2/3] qga/win/vss: query VSS backup type

[Kfir Manor]

Query VSS backup type number (DWORD) from QEMU Guest Agent VSS Provider 
registry key registry value VssOption

Translate the VSS backup type number (DWORD) into its VSS backup type 
(VSS_BACKUP_TYPE)

Returns the queried VSS backup type if the program encounters unexpected 
behaviors or values return default VSS backup type VSS_BT_FULL instead

Signed-off-by: Kfir Manor <kfir@daynix.com>
---
 qga/vss-win32/requester.cpp | 38 +++++++++++++++++++++++++++++++++++++
 qga/vss-win32/vss-handles.h |  3 +++
 2 files changed, 41 insertions(+)

diff --git a/qga/vss-win32/requester.cpp b/qga/vss-win32/requester.cpp
index b371affeab..27fdb9236b 100644
--- a/qga/vss-win32/requester.cpp
+++ b/qga/vss-win32/requester.cpp
@@ -23,6 +23,8 @@
 /* Call QueryStatus every 10 ms while waiting for frozen event */
 #define VSS_TIMEOUT_EVENT_MSEC 10
 
+#define DEFAULT_VSS_BACKUP_TYPE VSS_BT_FULL
+
 #define err_set(e, err, fmt, ...)                                           \
     ((e)->error_setg_win32_wrapper((e)->errp, __FILE__, __LINE__, __func__, \
                                    err, fmt, ## __VA_ARGS__))
@@ -234,6 +236,42 @@ out:
     }
 }
 
+DWORD get_reg_dword_value(HKEY baseKey, LPCSTR subKey, LPCSTR valueName,
+                          DWORD defaultData)
+{
+    DWORD regGetValueError;
+    DWORD dwordData;
+    DWORD dataSize = sizeof(DWORD);
+
+    regGetValueError = RegGetValue(baseKey, subKey, valueName, RRF_RT_DWORD,
+                                   NULL, &dwordData, &dataSize);
+    if (regGetValueError  != ERROR_SUCCESS) {
+        return defaultData;
+    }
+    return dwordData;
+}
+
+bool is_valid_vss_backup_type(VSS_BACKUP_TYPE vssBT)
+{
+    return (vssBT > VSS_BT_UNDEFINED && vssBT < VSS_BT_OTHER);
+}
+
+VSS_BACKUP_TYPE get_vss_backup_type(
+    VSS_BACKUP_TYPE defaultVssBT = DEFAULT_VSS_BACKUP_TYPE)
+{
+    VSS_BACKUP_TYPE vssBackupType;
+
+    vssBackupType = static_cast<VSS_BACKUP_TYPE>(
+                            get_reg_dword_value(HKEY_LOCAL_MACHINE,
+                                                QGA_PROVIDER_REGISTRY_ADDRESS,
+                                                "VssOption",
+                                                defaultVssBT));
+    if (!is_valid_vss_backup_type(vssBackupType)) {
+        return defaultVssBT;
+    }
+    return vssBackupType;
+}
+
 void requester_freeze(int *num_vols, void *mountpoints, ErrorSet *errset)
 {
     COMPointer<IVssAsync> pAsync;
diff --git a/qga/vss-win32/vss-handles.h b/qga/vss-win32/vss-handles.h
index 0f8a741ad2..1a7d842129 100644
--- a/qga/vss-win32/vss-handles.h
+++ b/qga/vss-win32/vss-handles.h
@@ -6,6 +6,9 @@
 #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 QGA_PROVIDER_REGISTRY_ADDRESS "SYSTEM\\CurrentControlSet"\
+                                      "\\Services"\
+                                      "\\" QGA_PROVIDER_NAME
 
 #define EVENT_NAME_FROZEN  "Global\\QGAVSSEvent-frozen"
 #define EVENT_NAME_THAW    "Global\\QGAVSSEvent-thaw"
-- 
2.38.1