cowtest fixed and try to finish usertests

kernel/vm.c

@@ -6,6 +6,10 @@
 #include "defs.h"
 #include "fs.h"
 
+void incref(void *pa);
+void kfree(void *pa);
+void *kalloc(void);
+
 /*
  * the kernel's page table.
  */
@@ -315,7 +319,7 @@ 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)
@@ -324,19 +328,21 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
       panic("uvmcopy: page not present");
     pa = PTE2PA(*pte);
     flags = PTE_FLAGS(*pte);
-    if((mem = kalloc()) == 0)
-      goto err;
-    memmove(mem, (char*)pa, PGSIZE);
-    if(mappages(new, i, PGSIZE, (uint64)mem, flags) != 0){
-      kfree(mem);
-      goto err;
+    // 如果是可写页，去掉PTE_W，设置PTE_COW
+    if(flags & PTE_W) {
+      flags = (flags & ~PTE_W) | PTE_COW;
+      *pte = PA2PTE(pa) | flags;
     }
+    // 子页表同样映射，权限同上
+    if(mappages(new, i, PGSIZE, pa, flags) != 0){
+      // kfree(mem); // 不再分配新页
+      uvmunmap(new, 0, i / PGSIZE, 0);
+      return -1;
+    }
+    // 增加物理页引用计数
+    incref((void*)pa);
   }
   return 0;
-
- err:
-  uvmunmap(new, 0, i / PGSIZE, 1);
-  return -1;
 }
 
 // mark a PTE invalid for user access.
@@ -366,9 +372,25 @@ copyout(pagetable_t pagetable, uint64 dstva, char *src, uint64 len)
     if(va0 >= MAXVA)
       return -1;
     pte = walk(pagetable, va0, 0);
-    if(pte == 0 || (*pte & PTE_V) == 0 || (*pte & PTE_U) == 0 ||
-       (*pte & PTE_W) == 0)
+    if(pte == 0 || (*pte & PTE_V) == 0 || (*pte & PTE_U) == 0)
       return -1;
+    if((*pte & PTE_W) == 0) {
+      // COW处理
+      if((*pte & PTE_COW) != 0) {
+        pa0 = PTE2PA(*pte);
+        char *mem = kalloc();
+        if(mem == 0)
+          return -1;
+        memmove(mem, (void*)pa0, PGSIZE);
+        // 更新PTE为新物理页，可写，去掉COW
+        *pte = PA2PTE(mem) | PTE_FLAGS(*pte) | PTE_W;
+        *pte &= ~PTE_COW;
+        // 原物理页引用计数减一
+        kfree((void*)pa0);
+      } else {
+        return -1;
+      }
+    }
     pa0 = PTE2PA(*pte);
     n = PGSIZE - (dstva - va0);
     if(n > len)