Re: [PATCH 1/1] eventfd: implementation of EFD_MASK flag

[Martin Sustrik]

On 08/02/13 23:08, Eric Wong wrote:

> > > > > poll(2) function (POLLIN, POLLOUT, POLLERR, POLLHUP etc.) Specified
> > > > > events will
> > > > > be signaled when polling (select, poll, epoll) on the eventfd is done
> > > > > later on.
> > > > > 'ptr' is an opaque pointer that is not interpreted by eventfd object.
> > > >
> > > > How does this interact with EPOLLET?
> > >
> > > That's an interesting question. The original eventfd code doesn't do
> > > anything specific to either edge or level mode. Neither does my patch.
> > >
> > > Inspection of the code seems to suggest that edge vs. level distinction is
> > > handled elsewhere (ep_send_events_proc) where there is a separate list of
> > > ready events and the function, after returning the event, decides whether to
> > > leave the event in the list (level) or delete it from the list (edge).
>
> Right, the edge vs. level distinction is internal to epoll.

I wrote a test program for EFD_MASK+EPOLLET and it seems to behave in 
intuitive kind of way:

int main ()
{
    int fd;
    struct efd_mask mask;
    ssize_t nbytes;
    int rc;
    int ep;
    struct epoll_event epe;

    fd = eventfd (0, EFD_MASK);

    ep = epoll_create (10);
    assert (ep != -1);
    epe.events = EPOLLIN | EPOLLET;
    rc = epoll_ctl (ep, EPOLL_CTL_ADD, fd, &epe);
    assert (rc != -1);

    mask.events = 0;
    nbytes = write (fd, &mask, sizeof (mask));
    assert (nbytes == sizeof (mask));
    rc = epoll_wait (ep, &epe, 1, 100);
    assert (rc == 0);

    mask.events = POLLIN;
    nbytes = write (fd, &mask, sizeof (mask));
    assert (nbytes == sizeof (mask));
    rc = epoll_wait (ep, &epe, 1, 100);
    assert (rc == 1 && epe.events == EPOLLIN);
    rc = epoll_wait (ep, &epe, 1, 100);
    assert (rc == 0);

    mask.events = POLLIN;
    nbytes = write (fd, &mask, sizeof (mask));
    mask.events = 0;
    nbytes = write (fd, &mask, sizeof (mask));
    rc = epoll_wait (ep, &epe, 1, 100);
    assert (rc == 0);

    rc = close (ep);
    assert (rc == 0);
    rc = close (fd);
    assert (rc == 0);

    return 0;
}

Martin
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