Fix potential bugs reported by CoverityScan (#5105)

- Change strncpy to StrNCpy, make sure dest string be terminated
- Initilize some variables before use it.

src/backend/commands/resgroupcmds.c

@@ -278,7 +278,6 @@ DropResourceGroup(DropResourceGroupStmt *stmt)
 	ScanKeyData	 scankey;
 	SysScanDesc	 sscan;
 	Oid			 groupid;
-	ResGroupCaps		caps;
 	ResourceGroupCallbackContext	*callbackCtx;
 
 	/* Permission check - only superuser can drop resource groups. */
@@ -480,7 +479,7 @@ AlterResourceGroup(AlterResourceGroupStmt *stmt)
 			caps.memAuditor = value;
 			break;
 		case RESGROUP_LIMIT_TYPE_CPUSET:
-			strncpy(caps.cpuset, cpuset, sizeof(caps.cpuset));
+			StrNCpy(caps.cpuset, cpuset, sizeof(caps.cpuset));
 			caps.cpuRateLimit = CPU_RATE_LIMIT_DISABLED;
 			break;
 		default:
@@ -627,7 +626,7 @@ GetResGroupCapabilities(Relation rel, Oid groupId, ResGroupCaps *resgroupCaps)
 												   getResgroupOptionName(type));
 				break;
 			case RESGROUP_LIMIT_TYPE_CPUSET:
-				strncpy(resgroupCaps->cpuset, proposed, sizeof(resgroupCaps->cpuset));
+				StrNCpy(resgroupCaps->cpuset, proposed, sizeof(resgroupCaps->cpuset));
 				break;
 			default:
 				break;
@@ -1038,7 +1037,7 @@ parseStmtOptions(CreateResourceGroupStmt *stmt, ResGroupCaps *caps)
 		{
 			const char *cpuset = defGetString(defel);
 			checkCpusetSyntax(cpuset);
-			strncpy(caps->cpuset, cpuset, sizeof(caps->cpuset));
+			StrNCpy(caps->cpuset, cpuset, sizeof(caps->cpuset));
 			caps->cpuRateLimit = CPU_RATE_LIMIT_DISABLED;
 		}
 		else 
@@ -1255,7 +1254,7 @@ updateResgroupCapabilityEntry(Relation rel,
 
 	if (limitType == RESGROUP_LIMIT_TYPE_CPUSET)
 	{
-		strncpy(stringBuffer, strValue, sizeof(stringBuffer));
+		StrNCpy(stringBuffer, strValue, sizeof(stringBuffer));
 	}
 	else
 	{

src/backend/utils/resgroup/resgroup-ops-linux.c

@@ -667,7 +667,7 @@ readStr(Oid group, const char *base, const char *comp, const char *prop, char *s
 
 	readData(path, data, datasize);
 
-	strncpy(str, data, len);
+	StrNCpy(str, data, len);
 }
 
 /*
@@ -1176,7 +1176,7 @@ ResGroupOps_AssignGroup(Oid group, ResGroupCaps *caps, int pid)
 	if (caps != NULL)
 	{
 		oldCaps.cpuRateLimit = caps->cpuRateLimit;
-		strncpy(oldCaps.cpuset, caps->cpuset, sizeof(oldCaps.cpuset));
+		StrNCpy(oldCaps.cpuset, caps->cpuset, sizeof(oldCaps.cpuset));
 	}
 }
 

src/backend/utils/resgroup/resgroup.c

@@ -2450,7 +2450,7 @@ void
 SwitchResGroupOnSegment(const char *buf, int len)
 {
 	Oid		newGroupId;
-	ResGroupCaps		caps;
+	ResGroupCaps		caps = {0};
 	ResGroupData		*group;
 	ResGroupSlotData	*slot;
 
@@ -3809,7 +3809,7 @@ bool CpusetIsEmpty(const char *cpuset)
  */
 void SetCpusetEmpty(char *cpuset, int cpusetSize)
 {
-	strncpy(cpuset, DefaultCpuset, cpusetSize);
+	StrNCpy(cpuset, DefaultCpuset, cpusetSize);
 }
 
 /*