[Xenomai-help] read returns more bytes than requested?

[Jeff Webb <jeff.webb@domain.hid>]

I am having some success porting my RTLinux application, but I have encountered a strange error.

I have this snippet of code that is reading data from an rtai-skin FIFO:

  result = read(runtime2io_fd, &resp, sizeof(resp));
  if (result != sizeof(resp))
    {
      printf("requested %d bytes, got %d\n", sizeof(resp), result);
      snprintf(err_str, MAX_STR_LEN, "cannot read response from %s",
               RUNTIME2IO_FIFO_DEV);
      sim_halt(err_str);
      return;
    }

I get the following output:

  requested 312 bytes, got 1220
  halting the sim: cannot read response from /dev/rtf1

I didn't think that a read could return more bytes than was requested.  Does anyone understand this behaviour?  This is code that works under RT-Linux.  I am trying to determine why it is working differently under xenomai.

-Jeff