Re: [Qemu-devel] [RFC v6 18/27] monitor: send event when command queue full

[Fam Zheng <famz@redhat.com>]

On Mon, 12/25 13:18, Peter Xu wrote:
> On Thu, Dec 21, 2017 at 07:42:46PM +0800, Fam Zheng wrote:
> > On Tue, 12/19 16:45, Peter Xu wrote:
> > > Set maximum QMP command queue length to 8.  If queue full, instead of
> > > queue the command, we directly return a "command-dropped" event, telling
> > > client that specific command is dropped.
> > > 
> > > Note that this flow control mechanism is only valid if OOB is enabled.
> > > If it's not, the effective queue length will always be 1, which strictly
> > > follows original behavior of QMP command handling (which never drop
> > > messages).
> > > 
> > > Signed-off-by: Peter Xu <peterx@redhat.com>
> > > ---
> > >  monitor.c | 17 ++++++++++++++++-
> > >  1 file changed, 16 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/monitor.c b/monitor.c
> > > index ed9a741d06..b571866659 100644
> > > --- a/monitor.c
> > > +++ b/monitor.c
> > > @@ -4038,6 +4038,8 @@ static void monitor_qmp_bh_dispatcher(void *data)
> > >      }
> > >  }
> > >  
> > > +#define  QMP_REQ_QUEUE_LEN_MAX  (8)
> > 
> > Is this limit introspectable on QMP?
> 
> Not yet.  IMHO it's really QMP internal stuff, and I see no benefit so
> far for a client to know about this...

A client may need this number to batch (non-oob) commands without worrying about
getting command-dropped event.

Fam