three quesions about filesytem

[shizheng]

Hi:

   1.

      rtems_libio_is_valid_perms always returns non-zero value,
      so I can't catch why it's called in IMFS_evaluate_permission and IMFS_eval_path.

      #define RTEMS_LIBIO_PERMS_RWX    S_IRWXO
      /*
       * Verifies that the permission flag is valid.
       */
      #define rtems_libio_is_valid_perms( _perm )     \
       (~ ((~RTEMS_LIBIO_PERMS_RWX) & _perm ))

          

   2. Why isn't there a semaphore and reference count to protect IMFS
      nodes like dosfs?
      Let's suppose / and /mem are IMFS_DIRECTORY nodes, and
      /mem/file is an IMFS_MEMORY_FILE node. Then I can delete
      /mem/file while it's still in open progress. To prove this, you
      can create two task:

      rtems_task imfs_reader(rtems_task_argument argument)
      {
      int open_status, stat_status;
      struct stat stat_buf;
      rtems_id tid;

      rtems_task_ident( RTEMS_SELF, RTEMS_SEARCH_ALL_NODES, &tid );
      printf( "imfs_reader task was invoked with argument (%d) "
      "and has id of 0x%x\n", argument, tid );

      while(1){
      open_status = open("/dev/test", 0);
      sleep(2+argument);
      stat_status = stat("/dev/test", &stat_buf);
      if(open_status>=0 && stat_status==-1){
      printf("file deleted while still opened\n", argument);
      Print_time();
      exit(0);
      }
      close(open_status);
      }
      }

      rtems_task imfs_writer(rtems_task_argument argument)
      {
      rtems_id tid;

      rtems_task_ident( RTEMS_SELF, RTEMS_SEARCH_ALL_NODES, &tid );
      printf( "imfs_writer task was invoked with argument (%d) "
      "and has id of 0x%x\n", argument, tid );

      while(1){
      mknod("/dev/test", 0777|S_IFCHR, 0);
      sleep(2+argument);
      unlink("/dev/test");
      sleep(2+argument);
      }
      }

      After about 4 seconds, you can see "file deleted while still
      opened" on the screen.


   3. imfs_dir_close doesn't check the st_nlink member of an IMFS
      directory node.
      So such a scenario will cause memory leak:
         1. suppose /emptydir is an empty IMFS directory
         2. dirp = opendir("/emptydir");
            rmdir("/emptydir");
            closedir(dirp);
         3. After rmdir calls imfs_dir_rmnod, the IMFS node of /emptydir
            has been
            Chain_Extract from the IMFS name tree, but can't be freed as
            a result of
            opendir. Because imfs_dir_close doesn't do any check, this
            IMFS node
            will never be freed.


Question No 2 and 3 are very obvious, I'm very confused why you guys
remain the code
like that, so I guess you may think it's the application-user's
responsiblity to do
the synchronization, but why dosfs does the effort while IMFS doesn't.

Thank you very much for bringing us such a good open-source real-time os
to the world:)))


best wishes from shizheng, University of Science and Technology of China

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