From 723055f4855ed8f2237cb9d4629518a5b76cbd0f Mon Sep 17 00:00:00 2001
From: Themis Demetriades <td1223@ic.ac.uk>
Date: Wed, 4 Dec 2024 21:33:21 +0000
Subject: [PATCH] fix: only use lazy loading if VM flag is enabled

---
 src/threads/thread.c     | 13 ++++++---
 src/userprog/exception.c |  3 +++
 src/userprog/process.c   | 57 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 69 insertions(+), 4 deletions(-)

diff --git a/src/threads/thread.c b/src/threads/thread.c
index c2944cc..b512aee 100644
--- a/src/threads/thread.c
+++ b/src/threads/thread.c
@@ -259,14 +259,19 @@ thread_create (const char *name, int priority,
       return TID_ERROR;
     }
 
+#define USERPROG
 #ifdef USERPROG
   /* Initialize the thread's file descriptor table. */
   t->fd_counter = MINIMUM_USER_FD;
 
-  if (!hash_init (&t->open_files, fd_hash, fd_less, NULL)
-      || !hash_init (&t->child_results, process_result_hash,
-                     process_result_less, t)
-      || !hash_init (&t->pages, page_hash, page_less, NULL))
+  bool success = hash_init (&t->open_files, fd_hash, fd_less, NULL);
+  success = success && hash_init (&t->child_results, process_result_hash,
+                                  process_result_less, t);
+#ifdef VM
+  success = success && hash_init (&t->pages, page_hash, page_less, NULL);
+#endif
+
+  if (!success)
     {
       palloc_free_page (t);
       free (t->result);
diff --git a/src/userprog/exception.c b/src/userprog/exception.c
index ed6a6ba..4e104d5 100644
--- a/src/userprog/exception.c
+++ b/src/userprog/exception.c
@@ -215,6 +215,7 @@ page_fault (struct intr_frame *f)
   kill (f);
 }
 
+#ifdef VM
 bool
 try_fetch_page (void *upage, bool write)
 {
@@ -244,3 +245,5 @@ try_fetch_page (void *upage, bool write)
 
   return success;
 }
+#endif
+
diff --git a/src/userprog/process.c b/src/userprog/process.c
index f4a7439..9ef5282 100644
--- a/src/userprog/process.c
+++ b/src/userprog/process.c
@@ -365,7 +365,9 @@ process_exit (void)
 
   /* Clean up all open files */
   hash_destroy (&cur->open_files, fd_cleanup);
+#ifdef VM
   hash_destroy (&cur->pages, page_cleanup);
+#endif
 
   /* Close the executable file, implicitly allowing it to be written to. */
   if (cur->exec_file != NULL)
@@ -623,6 +625,9 @@ load (const char *file_name, void (**eip) (void), void **esp)
 
  done:
   /* We arrive here whether the load is successful or not. */
+#ifndef VM
+  file_close (file);
+#endif
   lock_release (&filesys_lock);
   return success;
 }
@@ -696,6 +701,7 @@ load_segment (struct file *file, off_t ofs, uint8_t *upage,
   ASSERT (pg_ofs (upage) == 0);
   ASSERT (ofs % PGSIZE == 0);
 
+#ifdef VM
   while (read_bytes > 0 || zero_bytes > 0)
     {
       /* Calculate how to fill this page.
@@ -716,6 +722,57 @@ load_segment (struct file *file, off_t ofs, uint8_t *upage,
       upage += PGSIZE;
     }
   return true;
+#else
+  file_seek (file, ofs);
+  while (read_bytes > 0 || zero_bytes > 0) 
+    {
+      /* Calculate how to fill this page.
+         We will read PAGE_READ_BYTES bytes from FILE
+         and zero the final PAGE_ZERO_BYTES bytes. */
+      size_t page_read_bytes = read_bytes < PGSIZE ? read_bytes : PGSIZE;
+      size_t page_zero_bytes = PGSIZE - page_read_bytes;
+      
+      /* Check if virtual page already allocated */
+      struct thread *t = thread_current ();
+      uint8_t *kpage = pagedir_get_page (t->pagedir, upage);
+      
+      if (kpage == NULL){
+        
+        /* Get a new page of memory. */
+        kpage = get_usr_kpage (0, upage);
+        if (kpage == NULL){
+          return false;
+        }
+        
+        /* Add the page to the process's address space. */
+        if (!install_page (upage, kpage, writable)) 
+        {
+          free_usr_kpage (kpage);
+          return false; 
+        }     
+        
+      } else {
+        
+        /* Check if writable flag for the page should be updated */
+        if(writable && !pagedir_is_writable(t->pagedir, upage)){
+          pagedir_set_writable(t->pagedir, upage, writable); 
+        }
+        
+      }
+
+      /* Load data into the page. */
+      if (file_read (file, kpage, page_read_bytes) != (int) page_read_bytes){
+        return false; 
+      }
+      memset (kpage + page_read_bytes, 0, page_zero_bytes);
+
+      /* Advance. */
+      read_bytes -= page_read_bytes;
+      zero_bytes -= page_zero_bytes;
+      upage += PGSIZE;
+    }
+  return true;
+#endif
 }
 
 /* Create a minimal stack by mapping a zeroed page at the top of