support process group

kernel/include/process.h

@@ -194,6 +194,7 @@ struct process {
 
 	cpu_set_t cpu_set;
 	unsigned long saved_auxv[AUXV_LEN];
+	int pgid;	/* process group id */
 };
 
 struct process_vm {

kernel/include/syscall.h

@@ -110,6 +110,7 @@ struct program_load_desc {
 	int pid;
 	int err;
 	int stack_prot;
+	int pgid;
 	unsigned long entry;
 	unsigned long user_start;
 	unsigned long user_end;