Merge branch 'Alex/21-implement-filesize-system-call' into 'feature/system-calls'

Implemented filesize system call

See merge request !6

userprog/syscall.c

@@ -79,6 +79,9 @@ syscall_handler (struct intr_frame *f UNUSED)
   case SYSCALL_OPEN:
     syscall_open(f);
 	break;
+  case SYSCALL_FILESIZE:
+	syscall_filesize(f);
+	break;
   default:
     printf ("WARNING: Invalid Syscall (%d)\n", syscall_number);
     thread_exit ();

userprog/syscall_filesize.c

+/*
+ * Returns the size, in bytes, of the file open as fd.
+ *
+ * Authored by Alex Stratford
+ */
+
+#include "system_calls.h"
+#include "filesys/file.h"
+
+void syscall_filesize(struct intr_frame *f) {
+	// pop off first int argument from interrupt frame
+	int file_descriptor = *((int*)f->esp + 1);
+	struct file *file = get_associated_file_pointer(file_descriptor);
+	if (file == NULL) { // Checking if file is empty or non-existent
+		f->eax -1; // Returning failure state
+	}
+	// Using the file_length function in file.h to get the length and store it
+	int size = file_length(file); 
+	f->eax = size;
+}
\ No newline at end of file

userprog/system_calls.h

@@ -49,6 +49,11 @@ void syscall_write(struct intr_frame *f);
  */
 void syscall_open(struct intr_frame *f);
 
+/*
+ * Returns the size, in bytes, of the file open as fd.
+ */
+void syscall_filesize(struct intr_frame *f);
+
 /*
  * Deletes the file called file. Returns true if successful, false otherwise.
  * A file may be removed regardless of whether it is open or closed, and