Re: [Qemu-devel] [RFC PATCH v5 01/14] util: introduce gsource event abstraction

[Stefan Hajnoczi <stefanha@redhat.com>]

On Sat, Apr 27, 2013 at 10:11:40AM +0800, liu ping fan wrote:
> On Fri, Apr 26, 2013 at 5:19 PM, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > On Fri, Apr 26, 2013 at 10:47:22AM +0800, Liu Ping Fan wrote:
> >> +GPollFD *events_source_add_gfd(EventsGSource *src, int fd)
> >> +{
> >> +    GPollFD *retfd;
> >> +
> >> +    retfd = g_slice_alloc(sizeof(GPollFD));
> >> +    retfd->events = 0;
> >> +    retfd->fd = fd;
> >> +    src->pollfds_list = g_list_append(src->pollfds_list, retfd);
> >> +    if (fd > 0) {
> >
> > 0 (stdin) is a valid fd number.  Maybe just assert(fd >= 0)?
> >
> Yes, 0 should be allowed.   Here, the reason to use check instead of
> assert , is that socreate() in slirp is a good place to call
> _add_gfd,  but unfortunately, at that time, its socket handler so->s =
> -1;   So we create the GPollFD ahead, and delay to call
> g_source_add_poll()

ok

> >> +static gboolean events_source_check(GSource *src)
> >> +{
> >> +    EventsGSource *nsrc = (EventsGSource *)src;
> >> +    GList *cur;
> >> +    GPollFD *gfd;
> >> +
> >> +    cur = nsrc->pollfds_list;
> >> +    while (cur) {
> >> +        gfd = cur->data;
> >> +        if (gfd->fd > 0 && (gfd->revents & gfd->events)) {
> >
> > revents will always be 0 if fd is invalid, since we didn't call
> > g_source_add_poll().  Is there a reason to perform the fd > 0 check
> > again?
> >
> As explained above, we should skip the case gfd->fd=-1, which may
> occur in pollfds_list.

ok

> >> +void events_source_release(EventsGSource *src)
> >> +{
> >
> > assert that pollfds_list is empty?  We don't g_slice_free() GPollFDs so
> > it must be empty here.
> 
> Do you mean that   events_source_add_gfd/events_source_remove_gfd are
> paired, so here, we ensure that pollfds_list==NULL ?

Yes.  It is an error to hold a GPollFD across events_source_release() so
you could place an assert() here to check.

Stefan