Re: proposal: module 'accept4'

[Bruno Haible]

Eric Blake wrote:
> >       nfd = _open_osfhandle ((long) new_handle,
> >                          O_NOINHERIT | (flags & (O_TEXT | O_BINARY)));
> >       if (nfd < 0)
> >     {
> >       int saved_errno = errno;
> >       close (fd);
> >       errno = saved_errno;
> >       return -1;
> >     }
> >
> >       close (fd);
> >       return nfd;
> 
> This means that nfd > fd, so there is a gap in the fd sequence which is
> unexpected per POSIX rules.  Is it worth the hassle of using
> dup2(nfd,fd),close(fd) instead of close(fd)?

Good point. This gap can be avoided like this:

  if (flags & SOCK_CLOEXEC)
    {
      HANDLE curr_process = GetCurrentProcess ();
      HANDLE old_handle = (HANDLE) _get_osfhandle (fd);
      HANDLE new_handle;

      if (!DuplicateHandle (curr_process,           /* SourceProcessHandle */
                            old_handle,             /* SourceHandle */
                            curr_process,           /* TargetProcessHandle */
                            (PHANDLE) &new_handle,  /* TargetHandle */
                            (DWORD) 0,              /* DesiredAccess */
                            FALSE,                  /* InheritHandle */
                            DUPLICATE_SAME_ACCESS)) /* Options */
        {
          close (fd);
          errno = EBADF; /* arbitrary */
          return -1;
        }

      /* Closing fd before allocating the new fd ensures that the new fd will
         have the minimum possible value.  */
      close (fd);
      return _open_osfhandle ((long) new_handle,
                              O_NOINHERIT | (flags & (O_TEXT | O_BINARY)));
    }

> >   if (flags & SOCK_CLOEXEC)
> >     {
> >       int fcntl_flags;
> >
> >       if ((fcntl_flags = fcntl (fd, F_GETFD, 0)) < 0
> >       || fcntl (fd, F_SETFD, fcntl_flags | FD_CLOEXEC) < 0)
> 
> Success for F_SETFD is like F_SETFL - you must compare against explicit -1.

Done.

> Do you have a test case in mind?

Not on this one. It's expensive to write a test for this one.

Bruno