Re: [bug-gnulib] poll(2) emulation doesn't work well on a file descriptor

[Bruno Haible]

Daiki Ueno wrote:
> When I tried a tiny program which uses gnulib's poll(2) emulation on
> MacOS X 10.4, I found a bug.  gnulib's poll(2) uses recv(2) with
> MSG_PEEK to support POLLHUP.  However, recv(2) is only applicable to a
> socket, not to a file descriptor.

Thanks for reporting this.

> Though I don't know how to fix it, I think it can be by-passed if
> (pfd[i].events & POLLHUP) == 0?  Here is the patch
> 
> Index: poll.c
> ===================================================================
> RCS file: /sources/gnulib/gnulib/lib/poll.c,v
> retrieving revision 1.4
> diff -u -r1.4 poll.c
> --- poll.c    19 Sep 2005 17:28:14 -0000      1.4
> +++ poll.c    11 Aug 2006 07:32:03 -0000
> @@ -155,7 +155,8 @@
>           {
>             /* support for POLLHUP.  An hung up descriptor does not
>                increase the return value! */
> -           if (recv (pfd[i].fd, data, 64, MSG_PEEK) == -1)
> +           if (pfd[i].events & POLLHUP &&
> +               recv (pfd[i].fd, data, 64, MSG_PEEK) == -1)
>               {
>                 if (errno == ESHUTDOWN || errno == ECONNRESET
>                     || errno == ECONNABORTED || errno == ENETRESET)

This is not right: it tests for POLLHUP in the 'events' bit mask.
POSIX says "This flag is only valid  in the revents bitmask; it shall be
ignored in the events member.".

Paolo, is the appended patch ok to commit? (Includes a move from K&R C
to ANSI C. gnulib assumes ANSI C now for a year or two.)

Bruno


*** poll.c      19 Sep 2005 17:28:14 -0000      1.4
--- poll.c      11 Aug 2006 18:44:33 -0000
***************
*** 1,7 ****
  /* Emulation for poll(2)
     Contributed by Paolo Bonzini.
  
!    Copyright 2001, 2002, 2003 Free Software Foundation, Inc.
  
     This file is part of gnulib.
  
--- 1,7 ----
  /* Emulation for poll(2)
     Contributed by Paolo Bonzini.
  
!    Copyright 2001-2003, 2006 Free Software Foundation, Inc.
  
     This file is part of gnulib.
  
***************
*** 51,60 ****
  #endif
  
  int
! poll (pfd, nfd, timeout)
!      struct pollfd *pfd;
!      nfds_t nfd;
!      int timeout;
  {
    fd_set rfds, wfds, efds;
    struct timeval tv, *ptv;
--- 51,57 ----
  #endif
  
  int
! poll (struct pollfd *pfd, nfds_t nfd, int timeout)
  {
    fd_set rfds, wfds, efds;
    struct timeval tv, *ptv;
***************
*** 155,161 ****
            {
              /* support for POLLHUP.  An hung up descriptor does not
                 increase the return value! */
!             if (recv (pfd[i].fd, data, 64, MSG_PEEK) == -1)
                {
                  if (errno == ESHUTDOWN || errno == ECONNRESET
                      || errno == ECONNABORTED || errno == ENETRESET)
--- 152,159 ----
            {
              /* support for POLLHUP.  An hung up descriptor does not
                 increase the return value! */
!             if (recv (pfd[i].fd, data, 64, MSG_PEEK) == -1
!                 && errno != ENOTSOCK)
                {
                  if (errno == ESHUTDOWN || errno == ECONNRESET
                      || errno == ECONNABORTED || errno == ENETRESET)