From 1540c8b15ac35de9027e60804a786d23703d383d Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Tue, 2 Jul 2019 11:04:35 -0400
Subject: [PATCH] COW tests

---
 kernel/vm.c |   2 +-
 user/cow.c  | 144 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 144 insertions(+), 2 deletions(-)

diff --git a/kernel/vm.c b/kernel/vm.c
index 7d67464..d5ff594 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -97,8 +97,8 @@ walk(pagetable_t pagetable, uint64 va, int alloc)
 }
 
 // Look up a virtual address, return the physical address,
-// Can only be used to look up user pages.
 // or 0 if not mapped.
+// Can only be used to look up user pages.
 uint64
 walkaddr(pagetable_t pagetable, uint64 va)
 {
diff --git a/user/cow.c b/user/cow.c
index f770cc9..45efc98 100644
--- a/user/cow.c
+++ b/user/cow.c
@@ -43,12 +43,154 @@ simpletest()
     exit();
   }
 
-  printf(1, "simple ok\n");
+  printf(1, "ok\n");
+}
+
+// three processes all write COW memory.
+// this causes more than half of physical memory
+// to be allocated, so it also checks whether
+// copied pages are freed.
+void
+threetest()
+{
+  uint64 phys_size = PHYSTOP - KERNBASE;
+  int sz = phys_size / 4;
+  int pid1, pid2;
+
+  printf(1, "three: ");
+  
+  char *p = sbrk(sz);
+  if(p == (char*)0xffffffffffffffffL){
+    printf(1, "sbrk(%d) failed\n", sz);
+    exit();
+  }
+
+  pid1 = fork();
+  if(pid1 < 0){
+    printf(1, "fork failed\n");
+    exit();
+  }
+  if(pid1 == 0){
+    pid2 = fork();
+    if(pid2 < 0){
+      printf(1, "fork failed");
+      exit();
+    }
+    if(pid2 == 0){
+      for(char *q = p; q < p + (sz/5)*4; q += 4096){
+        *(int*)q = getpid();
+      }
+      for(char *q = p; q < p + (sz/5)*4; q += 4096){
+        if(*(int*)q != getpid()){
+          printf(1, "wrong content\n");
+          exit();
+        }
+      }
+      exit();
+    }
+    for(char *q = p; q < p + (sz/2); q += 4096){
+      *(int*)q = 9999;
+    }
+    exit();
+  }
+
+  for(char *q = p; q < p + sz; q += 4096){
+    *(int*)q = getpid();
+  }
+
+  wait();
+
+  sleep(1);
+
+  for(char *q = p; q < p + sz; q += 4096){
+    if(*(int*)q != getpid()){
+      printf(1, "wrong content\n");
+      exit();
+    }
+  }
+
+  if(sbrk(-sz) == (char*)0xffffffffffffffffL){
+    printf(1, "sbrk(-%d) failed\n", sz);
+    exit();
+  }
+
+  printf(1, "ok\n");
+}
+
+char junk1[4096];
+int fds[2];
+char junk2[4096];
+char buf[4096];
+char junk3[4096];
+
+// test whether copyout() simulates COW faults.
+void
+filetest()
+{
+  int parent = getpid();
+  
+  printf(1, "file test: ");
+  
+  buf[0] = 99;
+
+  for(int i = 0; i < 4; i++){
+    if(pipe(fds) != 0){
+      printf(1, "pipe() failed\n");
+      exit();
+    }
+    int pid = fork();
+    if(pid < 0){
+      printf(1, "fork failed\n");
+      exit();
+    }
+    if(pid == 0){
+      sleep(1);
+      if(read(fds[0], buf, sizeof(i)) != sizeof(i)){
+        printf(1, "read failed\n");
+        kill(parent);
+        exit();
+      }
+      sleep(1);
+      int j = *(int*)buf;
+      if(j != i){
+        printf(1, "read the wrong value\n");
+        kill(parent);
+        exit();
+      }
+      exit();
+    }
+    if(write(fds[1], &i, sizeof(i)) != sizeof(i)){
+      printf(1, "write failed\n");
+      exit();
+    }
+  }
+
+  for(int i = 0; i < 4; i++)
+    wait();
+
+  if(buf[0] != 99){
+    printf(1, "child overwrote parent\n");
+    exit();
+  }
+
+  printf(1, "ok\n");
 }
 
 int
 main(int argc, char *argv[])
 {
   simpletest();
+
+  // check that the first simpletest() freed the physical memory.
+  simpletest();
+
+  threetest();
+  threetest();
+  threetest();
+
+  filetest();
+
+  printf(1, "ALL COW TESTS PASSED\n");
+
   exit();
 }