maint: don't leave garbage on early API exit

Several APIs clear out a user input buffer before attempting to
populate it; but in a few cases we missed this memset if we
detect a reason for an early exit.  Note that these APIs
check for non-NULL arguments, and exit early with an error
message when NULL is passed in; which means that we must be
careful to avoid a NULL deref in order to get to that error
message.  Also, we were inconsistent on the use of
sizeof(virType) vs. sizeof(expression); the latter is more
robust if we ever change the type of the expression (although
such action is unlikely since these types are part of our
public API).

* src/libvirt.c (virDomainGetInfo, virDomainGetBlockInfo)
(virStoragePoolGetInfo, virStorageVolGetInfo)
(virDomainGetJobInfo, virDomainGetBlockJobInfo): Move memset
before any returns.
Signed-off-by: NEric Blake <eblake@redhat.com>

src/libvirt.c

@@ -4144,11 +4144,12 @@ virDomainGetInfo(virDomainPtr domain, virDomainInfoPtr info)
 
     virResetLastError();
 
+    if (info)
+        memset(info, 0, sizeof(*info));
+
     virCheckDomainReturn(domain, -1);
     virCheckNonNullArgGoto(info, error);
 
-    memset(info, 0, sizeof(virDomainInfo));
-
     conn = domain->conn;
 
     if (conn->driver->domainGetInfo) {
@@ -8449,12 +8450,13 @@ virDomainGetBlockInfo(virDomainPtr domain, const char *disk,
 
     virResetLastError();
 
+    if (info)
+        memset(info, 0, sizeof(*info));
+
     virCheckDomainReturn(domain, -1);
     virCheckNonNullArgGoto(disk, error);
     virCheckNonNullArgGoto(info, error);
 
-    memset(info, 0, sizeof(virDomainBlockInfo));
-
     conn = domain->conn;
 
     if (conn->driver->domainGetBlockInfo) {
@@ -13082,11 +13084,12 @@ virStoragePoolGetInfo(virStoragePoolPtr pool,
 
     virResetLastError();
 
+    if (info)
+        memset(info, 0, sizeof(*info));
+
     virCheckStoragePoolReturn(pool, -1);
     virCheckNonNullArgGoto(info, error);
 
-    memset(info, 0, sizeof(virStoragePoolInfo));
-
     conn = pool->conn;
 
     if (conn->storageDriver->storagePoolGetInfo) {
@@ -13951,11 +13954,12 @@ virStorageVolGetInfo(virStorageVolPtr vol,
 
     virResetLastError();
 
+    if (info)
+        memset(info, 0, sizeof(*info));
+
     virCheckStorageVolReturn(vol, -1);
     virCheckNonNullArgGoto(info, error);
 
-    memset(info, 0, sizeof(virStorageVolInfo));
-
     conn = vol->conn;
 
     if (conn->storageDriver->storageVolGetInfo){
@@ -17240,11 +17244,12 @@ virDomainGetJobInfo(virDomainPtr domain, virDomainJobInfoPtr info)
 
     virResetLastError();
 
+    if (info)
+        memset(info, 0, sizeof(*info));
+
     virCheckDomainReturn(domain, -1);
     virCheckNonNullArgGoto(info, error);
 
-    memset(info, 0, sizeof(virDomainJobInfo));
-
     conn = domain->conn;
 
     if (conn->driver->domainGetJobInfo) {
@@ -19379,14 +19384,15 @@ virDomainGetBlockJobInfo(virDomainPtr dom, const char *disk,
 
     virResetLastError();
 
+    if (info)
+        memset(info, 0, sizeof(*info));
+
     virCheckDomainReturn(dom, -1);
     conn = dom->conn;
 
     virCheckNonNullArgGoto(disk, error);
     virCheckNonNullArgGoto(info, error);
 
-    memset(info, 0, sizeof(*info));
-
     if (conn->driver->domainGetBlockJobInfo) {
         int ret;
         ret = conn->driver->domainGetBlockJobInfo(dom, disk, info, flags);