Refactor syscall: Use EXIT_FAILURE instead of magic numbers & close files on failure

src/userprog/syscall.c

@@ -138,7 +138,6 @@ syscall_exit (int status)
 }
 
 /* Executes a given command with the relevant args, by calling process_execute.
-   Acquires the filesystem lock as process_execute accesses the file system.
    Returns PID for the process that is running the CMD_LINE
  */
 static pid_t
@@ -146,9 +145,7 @@ syscall_exec (const char *cmd_line)
 {
   validate_user_string (cmd_line);
 
-  pid_t pid = process_execute(cmd_line);
-
-  return pid;
+  return process_execute (cmd_line); /* Returns the PID of the new process */
 }
 
 /* Handles the syscall of wait. Effectively a wrapper for process_wait as the
@@ -156,7 +153,7 @@ syscall_exec (const char *cmd_line)
 static int
 syscall_wait (pid_t pid)
 {
-  return process_wait (pid);
+  return process_wait (pid); /* Returns the exit status of the waited process */
 }
 
 /* Handles the syscall for file creation. First validates the user file
@@ -202,14 +199,17 @@ syscall_open (const char *file)
   struct file *ptr = filesys_open (file);
   lock_release (&filesys_lock);
   if (ptr == NULL)
-    return -1;
+    return EXIT_FAILURE;
 
   /* Allocate space for a struct representing a mapping from an FD to a struct
      file. */
   struct open_file *file_info
     = (struct open_file*) malloc (sizeof (struct open_file));
   if (file_info == NULL)
-    return -1;
+    {
+      file_close (ptr);
+      return EXIT_FAILURE;
+    }
 
   /* Populate the above struct, with a unique FD and the current open file */
   file_info->fd = fd_counter++;
@@ -230,7 +230,7 @@ syscall_filesize (int fd)
 {
   struct open_file *file_info = fd_get_file (fd);
   if (file_info == NULL)
-      return -1;
+      return EXIT_FAILURE;
 
   lock_acquire (&filesys_lock);
   int bytes = file_length (file_info->file);
@@ -249,7 +249,7 @@ syscall_read (int fd, void *buffer, unsigned size)
   /* Only console (fd = 0) or other files, not including STDOUT, (fd > 1) are
      allowed. */
   if (fd < 0 || fd == STDOUT_FILENO)
-    return -1;
+    return EXIT_FAILURE;
 
   validate_user_pointer (buffer, size);
 
@@ -267,7 +267,7 @@ syscall_read (int fd, void *buffer, unsigned size)
       /* Reading from a file. */
       struct open_file *file_info = fd_get_file (fd);
       if (file_info == NULL)
-        return -1;
+        return EXIT_FAILURE;
 
       lock_acquire (&filesys_lock);
       int bytes_written = file_read (file_info->file, buffer, size);