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Re: [PATCH] poll: fix regression in Win32 emulation of poll function


From: Daniel P. Berrange
Subject: Re: [PATCH] poll: fix regression in Win32 emulation of poll function
Date: Thu, 11 May 2017 14:20:55 +0100
User-agent: Mutt/1.8.0 (2017-02-23)

On Thu, May 11, 2017 at 03:15:46PM +0200, Bruno Haible wrote:
> Hi Daniel,
> 
> > it does not actually make poll() function correctly. We're still passing
> > HANDLE objects to the rpl_select() method, instead of calling
> > the native select() method.
> 
> I don't agree with your reasoning. The select() calls in lib/poll.c:511 and
> lib/poll.c:547 is not passing a HANDLE, rather it passes bit masks of FDs
> that correspond to SOCKETs.  Therefore I propose this patch:

Perhaps I'm mis-understanding, but I was looking at this code:

      h = (HANDLE) _get_osfhandle (pfd[i].fd);
      assure (h != NULL);
      if (IsSocketHandle (h))
        {
          int requested = FD_CLOSE;

          /* see above; socket handles are mapped onto select.  */
          if (sought & (POLLIN | POLLRDNORM))
            {
              requested |= FD_READ | FD_ACCEPT;
              FD_SET ((SOCKET) h, &rfds);
            }
          if (sought & (POLLOUT | POLLWRNORM | POLLWRBAND))
            {
              requested |= FD_WRITE | FD_CONNECT;
              FD_SET ((SOCKET) h, &wfds);
            }
          if (sought & (POLLPRI | POLLRDBAND))
            {
              requested |= FD_OOB;
              FD_SET ((SOCKET) h, &xfds);
            }

which takes the 'FD' and gets the associated SOCKET / HANDLE.
The 'xfds' fd_set is thus populated with a SOCKET, not a FD.

A few lines later we call select() with xfds.

The rpl_select() is expecting 'xfds' to be populated with
a FD, not a SOCKET / HANDLE.


> diff --git a/lib/poll.c b/lib/poll.c
> index c4b2127..2c6e879 100644
> --- a/lib/poll.c
> +++ b/lib/poll.c
> @@ -80,6 +80,14 @@
>     first argument, not any possible gnulib override.  */
>  # undef recv
>  
> +/* Here it does not matter whether we use the select() function from Windows,
> +   that works only when all indicated FDs correspond to sockets and that
> +   returns its error code in WSAGetLastError(), or the gnulib override that
> +   does not have this limitation and that returns its error code in errno.
> +   To simplify testing, use the lower-level Windows select() function
> +   always.  */
> +# undef select
> +
>  static BOOL IsConsoleHandle (HANDLE h)
>  {
>    DWORD mode;
> 

Regards,
Daniel
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