Merge branch 'cow' into net

Conflicts:
	.gitignore
	Makefile
	conf/lab.mk
	kernel/defs.h
	kernel/syscall.c
	kernel/vm.c
	user/pingpong.c
	user/user.h
	user/usys.pl

1 files changed, 32 insertions, 40 deletions

diff --git a/user/pingpong.c b/user/pingpong.c
index 6ed12e7..7b03a76 100644
--- a/user/pingpong.c
+++ b/user/pingpong.c
@@ -1,52 +1,44 @@
 #include "kernel/types.h"
-#include "kernel/stat.h"
 #include "user/user.h"
 
-#define N 5
-char buf[N];
+int
+main(int argc, char* argv[])
+{
+  int p[2];
 
-void
-pong(int *parent_to_child, int *child_to_parent) {
-  if (read(parent_to_child[0], buf, N) < 0) {
-    printf("read failed\n");
-  }
-  printf("%d: received %s\n", getpid(), buf);
-  if (write(child_to_parent[1], "pong", 4) != 4) {
-    printf("write failed\n");
+  if (argc > 1) {
+    fprintf(2, "usage: pingpong\n");
+    exit(1);
   }
-}
 
-void
-ping(int *parent_to_child, int *child_to_parent) {
-  
-  if (write(parent_to_child[1], "ping", 4) != 4) {
-    printf("write failed\n");
-  }
-  if (read(child_to_parent[0], buf, N) < 0) {
-    printf("read failed\n");
-  }
-  printf("%d: received %s\n", getpid(), buf);
-}
+  pipe(p);
 
-int
-main(int argc, char *argv[])
-{
-  int parent_to_child[2];
-  int child_to_parent[2];
+  int pid = fork();
 
-  int pid;
-
-  if (pipe(parent_to_child) < 0 || pipe(child_to_parent) < 0) {
-    printf("pipe failed\n");
-  }
-  if ((pid = fork()) < 0) {
-    printf("fork failed\n");
-  }
   if (pid == 0) {
-    pong(parent_to_child, child_to_parent);
-  } else {
-    ping(parent_to_child, child_to_parent);
+    short n;
+    read(p[0], &n, sizeof(n));
+    if (n == 42) {
+      fprintf(1, "%d: received ping\n", getpid());
+    }
+    n++;
+    write(p[1], &n, sizeof(n));
+    close(p[0]);
+    close(p[1]);
+    exit(0);
+  }
+
+  short n = 42;
+
+  write(p[1], &n, sizeof(n));
+  read(p[0], &n, sizeof(n));
+  if (n == 43) {
+    fprintf(1, "%d: received pong\n", getpid());
   }
-  
+  close(p[0]);
+  close(p[1]);
+
+  wait(0);
+
   exit(0);
 }