implement open()

1 files changed, 41 insertions, 3 deletions

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 8e5593f..e72ee0b 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -4,9 +4,10 @@
 #include "threads/interrupt.h"
 #include "threads/thread.h"
 
-#include "threads/init.h"
 #include "filesys/filesys.h"
 #include "filesys/off_t.h"
+#include "threads/init.h"
+#include "threads/malloc.h"
 
 static void syscall_handler (struct intr_frame *);
 
@@ -28,6 +29,42 @@ create (const char *filename, off_t initial_size)
   return filesys_create (filename, initial_size);
 }
 
+static int
+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;
+  }
+
+  struct file *file = filesys_open(filename);
+  if (!file) {
+    printf("[%s] open: couldn't find file %s\n", t->name, filename);
+    return -1;
+  }
+
+  for (int i = 0; i < t->max_files; i++) {
+    struct fd *fd = t->files + i;
+    if (!fd->active) {
+      fd->active = true;
+      fd->file = file;
+      return i + 2;  // 0 and 1 are reserved for stdin and stdout
+    }
+  }
+  free(file);
+  printf("[%s] open: unable to find empty file descriptor\n", t->name);
+  return -1;
+}
+
 static void
 write (const char *buf)
 {
@@ -40,7 +77,7 @@ write (const char *buf)
 static void
 syscall_handler (struct intr_frame *f UNUSED) 
 {
-  int syscall_number = INTR_ESP(0, int);
+  int syscall_number = INTR_ESP (0, int);
   switch (syscall_number) {
     case 0:
       // halt
@@ -51,10 +88,11 @@ syscall_handler (struct intr_frame *f UNUSED)
       break;
     case 4:
       // create
-      f->eax = create(INTR_ESP(1, char *), INTR_ESP(2, off_t));
+      f->eax = create (INTR_ESP (1, char *), INTR_ESP (2, off_t));
       break;
     case 6:
       // open
+      f->eax = open (INTR_ESP (1, char *));
       break;
     case 8:
       // read