Re: [Qemu-devel] [PATCH v7 09/23] monitor: allow using IO thread for parsing

[Peter Xu]

On Thu, Feb 22, 2018 at 03:50:47PM +0000, Daniel P. Berrangé wrote:
> On Thu, Feb 22, 2018 at 06:01:19PM +0800, Peter Xu wrote:
> > On Wed, Feb 21, 2018 at 04:00:07PM +0000, Stefan Hajnoczi wrote:
> > > On Wed, Jan 24, 2018 at 01:39:43PM +0800, Peter Xu wrote:
> > > > @@ -4034,12 +4044,29 @@ static void sortcmdlist(void)
> > > >      qsort((void *)info_cmds, array_num, elem_size, compare_mon_cmd);
> > > >  }
> > > >  
> > > > +static GMainContext *monitor_io_context_get(void)
> > > > +{
> > > > +    return iothread_get_g_main_context(mon_global.mon_iothread);
> > > > +}
> > > > +
> > > > +static AioContext *monitor_aio_context_get(void)
> > > > +{
> > > > +    return iothread_get_aio_context(mon_global.mon_iothread);
> > > > +}
> > > 
> > > Please follow the X_get_Y() naming convention instead of X_Y_get().  For
> > > example, see qemu_get_aio_context() and iothread_get_aio_context().
> > 
> > Sure.
> > 
> > > 
> > > > @@ -4082,11 +4109,41 @@ void error_vprintf_unless_qmp(const char *fmt, 
> > > > va_list ap)
> > > >      }
> > > >  }
> > > >  
> > > > +static void monitor_list_append(Monitor *mon)
> > > > +{
> > > > +    qemu_mutex_lock(&monitor_lock);
> > > > +    QTAILQ_INSERT_HEAD(&mon_list, mon, entry);
> > > > +    qemu_mutex_unlock(&monitor_lock);
> > > > +}
> > > > +
> > > > +static void monitor_qmp_setup_handlers(void *data)
> > > 
> > > BH functions are usually declared like this:
> > > 
> > >   static void X_bh(void *opaque)
> > > 
> > > This way it's immediately clear that this function is invoked as a BH.
> > > 
> > > I suggest renaming the function to monitor_qmp_setup_handlers_bh().
> > > Using 'opaque' instead of 'data' is common, too.
> > 
> > Sure.
> > 
> > > 
> > > > @@ -4099,24 +4156,55 @@ void monitor_init(Chardev *chr, int flags)
> > > >      }
> > > >  
> > > >      if (monitor_is_qmp(mon)) {
> > > > -        qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read, 
> > > > monitor_qmp_read,
> > > > -                                 monitor_qmp_event, NULL, mon, NULL, 
> > > > true);
> > > >          qemu_chr_fe_set_echo(&mon->chr, true);
> > > >          json_message_parser_init(&mon->qmp.parser, handle_qmp_command);
> > > > +        if (mon->use_io_thr) {
> > > > +            /*
> > > > +             * It's possible that we already have an IOWatchPoll
> > > > +             * registered for the Chardev during chardev_init_func().
> > > 
> > > When does this happen?
> > > 
> > > This seems like a hack that breaks when certain -chardev options are
> > > used.  For example, what happens if the chardev is a TCP connection with
> > > reconnect=5.  In that case the socket will be connecting asynchronously
> > > and we cannot just remove the fd watch.
> > > 
> > > How does this interact with TCP listen chardevs?  It looks like the
> > > listener socket uses the main loop (see tcp_chr_disconnect()).
> > > 
> > > I'm worried that the chardev layer isn't thread-safe and you haven't
> > > added anything to protect it or at least refuse to run in unsafe
> > > conditions.
> > 
> > Indeed, I did some more reading and noticed that the TCP typed chardev
> > is really special.
> > 
> > Firstly there can be the QIO thread that handles sync connecting when
> > "reconnect" is setup (I don't really understand why we only need the
> > threads when reconnect != 0, but anyway, I'll just assume we need the
> > threads).  It's done in qmp_chardev_open_socket().
> > 
> > Secondly, TCP can support TLS or TELNET (tcp_chr_new_client() handles
> > the main logic of it), so there can be actually more than one GSource
> > created for a single TCP chardev.  Meanwhile, the
> > chr_update_read_handler() calls never handles the re-setup of those
> > special GSources (TLS/TELNET), only the common GSource of TCP stream
> > read/write.
> > 
> > And the whole TCP channel is based on QIO stuff, which means I need to
> > add non-default context support to QIO stuff too...  That's mostly
> > about qio_channel_add_watch().  I may need to pass in context
> > information, and switch to GSource for that function instead of the
> > old tags, just like what I did to chardev in general.
> 
> Rather than changing qio_channel_add_watch() which affects all callers,
> just add a qio_channel_add_watch_full() variant which includes  GMainContext
> as an extra arg

Yeh, will do.  Thanks,

-- 
Peter Xu