1 files changed, 27 insertions, 13 deletions

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index e72ee0b..0dd48b0 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -34,16 +34,9 @@ open (const char *filename)
 {
   struct thread *t = thread_current ();
 
-  if (t->max_files == 0) {
-    t->max_files = 128;
-    printf("[%s] open: allocating %d file descriptors\n", t->name, t->max_files);
-    t->files = (struct fd *) calloc (t->max_files, sizeof (struct fd));
-  }
-
-  if (t->num_files == t->max_files) {
-    // not enough space for more file descriptors
-    printf("[%s] open: too many file descriptors\n", t->name);
-    return -1;
+  if (!t->fds) {
+    printf("[%s] open: allocating %d file descriptors\n", t->name, MAX_FDS);
+    t->fds = (struct fd *) calloc (MAX_FDS, sizeof (struct fd));
   }
 
   struct file *file = filesys_open(filename);
@@ -52,8 +45,8 @@ open (const char *filename)
     return -1;
   }
 
-  for (int i = 0; i < t->max_files; i++) {
-    struct fd *fd = t->files + i;
+  for (int i = 0; i < MAX_FDS; i++) {
+    struct fd *fd = t->fds + i;
     if (!fd->active) {
       fd->active = true;
       fd->file = file;
@@ -71,6 +64,26 @@ write (const char *buf)
   printf ("printf: %s", buf);
 }
 
+static void
+close (int i)
+{
+  struct thread *t = thread_current ();
+
+  if (!t->fds) {
+    printf("[%s] close: no files have been opened\n", t->name);
+    return;
+  }
+
+  struct fd *fd = t->fds + i - 2; // -2 since 0 and 1 are reserved and not present in the array
+  if (!fd->active) {
+    printf("[%s] close: tried to close inactive file descriptor %d\n", t->name, i);
+    return;
+  }
+
+  free(fd->file);
+  fd->active = false;
+}
+
 // cast to TYPE and deref argument N from f->esp
 #define INTR_ESP(N, TYPE) *(TYPE *)(f->esp+(4*(N)))
 
@@ -99,10 +112,11 @@ syscall_handler (struct intr_frame *f UNUSED)
       break;
     case 9:
       // write
-      write(INTR_ESP(2, char *));
+      write (INTR_ESP(2, char *));
       break;
     case 12:
       // close
+      close (INTR_ESP(1, int));
       break;
     default:
       printf ("kernel: unknown syscall '%d'\n", syscall_number);