Lab util: pingpong

Makefile

@@ -142,6 +142,7 @@ UPROGS=\
 	$U/_ln\
 	$U/_ls\
 	$U/_mkdir\
+	$U/_pingpong\
 	$U/_rm\
 	$U/_sh\
 	$U/_sleep\

user/pingpong.c

@@ -0,0 +1,31 @@
+#include "kernel/types.h"
+#include "kernel/stat.h"
+#include "user/user.h"
+
+int
+main(int argc, char *argv[])
+{
+  if (argc > 1) {
+    fprintf(2, "Usage: pingpong\n");
+    exit(1);
+  }
+
+  int p[2];
+  char buf[4];
+
+  pipe(p);
+
+  if (fork() == 0) {
+    read(p[0], buf, 4);
+    fprintf(1, "%d: received %s\n", getpid(), buf);
+    write(p[1], "pong", 4);
+    exit(0);
+  } else {
+    write(p[1], "ping", 4);
+    wait(0);
+    read(p[0], buf, 4);
+    fprintf(1, "%d: received %s\n", getpid(), buf);
+  }
+
+  exit(0);
+}