Re: Incorrect behavior in TIOCINQ ioctl

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Feb 27 22:38, Åke Rehnman wrote:
> Hi,
> 
> I recently ran in to some troubles with the TIOCINQ ioctl. I am wondering if
> the cygwin implementation is correct... It seems if there were any existing
> framing overrun errors etc etc  before calling the TIOCINQ ioctl it is
> returning an error (EINVAL). Reading through linux implmentation of TIOCINQ
> does simply return number of pending chars without any clearing or checking
> for errors.
> 
> I suggest the whole if (ev & CE_FRAME  ...... ) is removed.
> 
> Excerpt from fhandler_serial.cc:
> 
> /* ioctl: */
> int
> fhandler_serial::ioctl (unsigned int cmd, void *buf)
> {
> .
> .
>   if (!ClearCommError (get_handle (), &ev, &st))
>     {
>       __seterrno ();
>       res = -1;
>     }
> .
> .
> .
>      case TIOCINQ:
>        if (ev & CE_FRAME || ev & CE_IOE || ev & CE_OVERRUN || ev & CE_RXOVER
>        || ev & CE_RXPARITY)
>      {
>        set_errno (EINVAL);    /* FIXME: Use correct errno */
>        res = -1;
>      }
>      else
>         ipbuf = st.cbInQue;
>      break;

I'm not familiar with serial I/O and the code is pretty stable(*).

- Is it a safe bet that ClearCommError returns valid values in
  st.cbInQue even if one of the error conditions occur?  Maybe the
  right thing to do is to return 0 in certain error cases...?

- Did you actually try if this fixes your problem?  It's pretty
  simple to build the Cygwin DLL
  https://cygwin.com/faq.html#faq.programming.building-cygwin


Corinna

(*) euphemistically for "nobody looked into the code for a long time"


-- 
Corinna Vinschen
Cygwin Maintainer

Attachment: signature.asc
Description: PGP signature