Use parent pointer instead of ppid.

proc.c

@@ -118,7 +118,7 @@ copyproc(struct proc *p)
   np->tf = (struct trapframe*)(np->kstack + KSTACKSIZE) - 1;
 
   if(p){  // Copy process state from p.
-    np->ppid = p->pid;
+    np->parent = p;
     memmove(np->tf, p->tf, sizeof(*np->tf));
   
     np->sz = p->sz;
@@ -366,15 +366,13 @@ proc_exit(void)
 
   acquire(&proc_table_lock);
 
-  // Wake up waiting parent.
-  for(p = proc; p < &proc[NPROC]; p++)
-    if(p->pid == cp->ppid)
-      wakeup1(p);
+  // Parent might be sleeping in proc_wait.
+  wakeup1(cp->parent);
 
   // Pass abandoned children to init.
   for(p = proc; p < &proc[NPROC]; p++){
-    if(p->ppid == cp->pid){
-      p->ppid = initproc->pid;
+    if(p->parent == cp){
+      p->parent = initproc;
       if(p->state == ZOMBIE)
         wakeup1(initproc);
     }
@@ -403,7 +401,7 @@ proc_wait(void)
       p = &proc[i];
       if(p->state == UNUSED)
         continue;
-      if(p->ppid == cp->pid){
+      if(p->parent == cp){
         if(p->state == ZOMBIE){
           // Found one.
           kfree(p->mem, p->sz);
@@ -411,7 +409,7 @@ proc_wait(void)
           pid = p->pid;
           p->state = UNUSED;
           p->pid = 0;
-          p->ppid = 0;
+          p->parent = 0;
           p->name[0] = 0;
           release(&proc_table_lock);
           return pid;

proc.h

@@ -33,7 +33,7 @@ struct proc {
   char *kstack;             // Bottom of kernel stack for this process
   enum proc_state state;    // Process state
   int pid;                  // Process ID
-  int ppid;                 // Parent pid
+  struct proc *parent;      // Parent process
   void *chan;               // If non-zero, sleeping on chan
   int killed;               // If non-zero, have been killed
   struct file *ofile[NOFILE];  // Open files