use struct **file instead of struct *fdlab1

Storing the null pointer to mark active == false accomplishes the same
thing with less storage.

3 files changed, 22 insertions, 45 deletions

diff --git a/src/filesys/filesys.h b/src/filesys/filesys.h
index 2db5b60..caef83c 100644
--- a/src/filesys/filesys.h
+++ b/src/filesys/filesys.h
@@ -17,12 +17,4 @@ bool filesys_create (const char *name, off_t initial_size);
 struct file *filesys_open (const char *name);
 bool filesys_remove (const char *name);
 
-#ifdef USERPROG
-struct fd
-  {
-    bool active;
-    struct file *file;
-  };
-#endif /* ifdef USERPROG */
-
 #endif /* filesys/filesys.h */
diff --git a/src/threads/thread.h b/src/threads/thread.h
index fc2029b..e3c426d 100644
--- a/src/threads/thread.h
+++ b/src/threads/thread.h
@@ -98,7 +98,7 @@ struct thread
 #ifdef USERPROG
     /* Owned by userprog/process.c. */
     uint32_t *pagedir;                  /* Page directory. */
-    struct fd *fds;                     /* Pointer to array of file descriptors. */
+    struct file **fds;                     /* Pointer to array of file descriptors. */
 #endif
 
     /* Owned by thread.c. */
diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index dc1f067..921ed44 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -37,7 +37,7 @@ open (const char *filename)
   struct thread *t = thread_current ();
 
   if (!t->fds) {
-    t->fds = (struct fd *) calloc (MAX_FDS, sizeof (struct fd));
+    t->fds = (struct file **) calloc (MAX_FDS, sizeof (struct file *));
   }
 
   struct file *file = filesys_open (filename);
@@ -46,10 +46,9 @@ open (const char *filename)
   }
 
   for (int i = 0; i < MAX_FDS; i++) {
-    struct fd *fd = t->fds + i;
-    if (!fd->active) {
-      fd->active = true;
-      fd->file = file;
+    struct file **fd = t->fds + i;
+    if (*fd == NULL) {
+      *fd = file;
       return i + 2;  // 0 and 1 are reserved for stdin and stdout
     }
   }
@@ -57,7 +56,7 @@ open (const char *filename)
   return -1;
 }
 
-static struct fd *
+static struct file **
 get_fd (struct thread *thread, int fd_i)
 {
   if (!thread->fds) {
@@ -67,18 +66,6 @@ get_fd (struct thread *thread, int fd_i)
   return thread->fds + fd_i - 2;  // -2 since 0 and 1 are reserved and not present in the array
 }
 
-static struct file *
-get_file (struct thread *thread, int fd_i)
-{
-  struct fd *fd = get_fd (thread, fd_i);
-
-  if (!fd || !fd->active) {
-    return NULL;
-  }
-
-  return fd->file;
-}
-
 static void
 exit (int status)
 {
@@ -86,10 +73,10 @@ exit (int status)
 
   if (thread->fds) {
     for (int i = 0; i < MAX_FDS; i++) {
-      struct fd *fd = thread->fds + i;
-      if (fd && fd->active) {
-        file_close (fd->file);
-        fd->active = false;
+      struct file **fd = thread->fds + i;
+      if (fd && *fd) {
+        file_close (*fd);
+        *fd = NULL;
       }
     }
     free (thread->fds);
@@ -113,12 +100,12 @@ read (int fd_i, void *buf, unsigned size)
     return -1;
   }
 
-  struct file *file = get_file (thread, fd_i);
-  if (!file) {
+  struct file **fd = get_fd (thread, fd_i);
+  if (fd && *fd) {
+    return file_read (*fd, buf, size);
+  } else {
     return -1;
   }
-
-  return file_read (file, buf, size);
 }
 
 static int
@@ -135,12 +122,12 @@ write (int fd_i, const void *buf, unsigned size)
     return -1;
   }
 
-  struct file *file = get_file (thread, fd_i);
-  if (!file) {
+  struct file **fd = get_fd (thread, fd_i);
+  if (fd && *fd) {
+    return file_write (*fd, buf, size);
+  } else {
     return -1;
   }
-
-  return file_write (file, buf, size);
 }
 
 static void
@@ -148,13 +135,11 @@ close (int fd_i)
 {
   struct thread *thread = thread_current ();
 
-  struct fd *fd = get_fd (thread, fd_i);
-  if (!fd || !fd->active) {
-    return;
+  struct file **fd = get_fd (thread, fd_i);
+  if (fd && *fd) {
+    file_close (*fd);
+    *fd = NULL;
   }
-
-  file_close (fd->file);
-  fd->active = false;
 }
 
 // cast to TYPE and deref argument N from f->esp