shell can launch another user processgit add .git add .!

kernel/process.h

@@ -12,6 +12,7 @@ typedef enum {
     STATE_SLEEPING = 2,
     STATE_BLOCKED = 3,
     STATE_DEAD = 4,
+    STATE_ZOMBIE = 5,
 } process_state_t;
 
 typedef enum {
@@ -32,6 +33,8 @@ typedef struct process_t {
     uint32_t flags;
     file_t* fd_table[MAX_PROCESS_FDS];
     struct process_t* sched_next;
+    struct process_t* waiting;
+    int exit_status;
 } __attribute__((packed)) process_t;
 
 #endif