lab cow: finishcow

1 files changed, 20 insertions, 7 deletions

diff --git a/kernel/vm.c b/kernel/vm.c
index 9c17fe7..11f9e0a 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -315,20 +315,26 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
   pte_t *pte;
   uint64 pa, i;
   uint flags;
-  char *mem;
+  // char *mem;
 
   for(i = 0; i < sz; i += PGSIZE){
     if((pte = walk(old, i, 0)) == 0)
       panic("uvmcopy: pte should exist");
     if((*pte & PTE_V) == 0)
       panic("uvmcopy: page not present");
-    pa = PTE2PA(*pte);
-    flags = PTE_FLAGS(*pte);
+    // do not do the actual copy, just increase the refcnt and mark pages readonly COW
+    /*
     if((mem = kalloc()) == 0)
       goto err;
     memmove(mem, (char*)pa, PGSIZE);
-    if(mappages(new, i, PGSIZE, (uint64)mem, flags) != 0){
-      kfree(mem);
+    */
+    *pte &= ~PTE_W;
+    *pte |= PTE_C;
+    pa = PTE2PA(*pte);
+    refcnt_inc(pa);
+    flags = PTE_FLAGS(*pte);
+    if(mappages(new, i, PGSIZE, (uint64)pa, flags) != 0){
+      // kfree(mem);
       goto err;
     }
   }
@@ -359,17 +365,24 @@ int
 copyout(pagetable_t pagetable, uint64 dstva, char *src, uint64 len)
 {
   uint64 n, va0, pa0;
-  pte_t *pte;
+  // pte_t *pte;
 
   while(len > 0){
     va0 = PGROUNDDOWN(dstva);
-    if(va0 >= MAXVA)
+
+    if(cow_handler(pagetable, va0) < 0)
       return -1;
+    
+    /*
     pte = walk(pagetable, va0, 0);
     if(pte == 0 || (*pte & PTE_V) == 0 || (*pte & PTE_U) == 0 ||
        (*pte & PTE_W) == 0)
       return -1;
     pa0 = PTE2PA(*pte);
+    */
+    pa0 = walkaddr(pagetable, va0);
+    if(pa0 == 0)
+      return -1;
     n = PGSIZE - (dstva - va0);
     if(n > len)
       n = len;