Fix rox checking and make filesys_lock global

Add validation to check for missing files in exec() args

See merge request lab2425_autumn/pintos_22!36

src/userprog/process.c

@@ -8,6 +8,7 @@
 #include <string.h>
 #include "userprog/gdt.h"
 #include "userprog/pagedir.h"
+#include "userprog/syscall.h"
 #include "userprog/tss.h"
 #include "filesys/directory.h"
 #include "filesys/file.h"
@@ -81,6 +82,10 @@ process_execute (const char *cmd)
      of the process. */
   char *file_name = strtok_r (cmd_copy, " ", &data->cmd_saveptr);
 
+  /* Validates that the current file to be executed is a valid file */
+  if (filesys_open (file_name) == NULL)
+    return TID_ERROR;
+
   /* Create a new thread to execute the command, by initializing
      it running the function 'start_process' with the appropriate
      arguments. For details of arguments, see 'start_process'. */

src/userprog/syscall.c

@@ -13,7 +13,6 @@
 #include <stdio.h>
 #include <syscall-nr.h>
 
-static struct lock filesys_lock;
 static unsigned fd_counter = MIN_USER_FD;
 
 struct open_file
@@ -143,9 +142,7 @@ syscall_exec (const char *cmd_line)
 {
   validate_user_pointer (cmd_line, 1);
 
-  lock_acquire (&filesys_lock);
   pid_t pid = process_execute(cmd_line);
-  lock_release (&filesys_lock);
 
   return pid;
 }

src/userprog/syscall.h

@@ -2,11 +2,14 @@
 #define USERPROG_SYSCALL_H
 
 #include <hash.h>
+#include "threads/synch.h"
 
 #define MIN_USER_FD 2
 
 typedef int pid_t;
 
+struct lock filesys_lock;
+
 void syscall_init (void);
 
 unsigned fd_hash (const struct hash_elem *element, void *aux);