Re: [Qemu-devel] [PATCH v7 4/7] qapi: remove COMMAND_DROPPED event

[Peter Xu <peterx@redhat.com>]

On Mon, Sep 03, 2018 at 09:49:13AM +0200, Markus Armbruster wrote:
> Peter Xu <peterx@redhat.com> writes:
> 
> > Now it was not used any more, drop it.  We can still do that since
> > out-of-band is still experimental, and this event is only used when
> > out-of-band is enabled.
> >
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  docs/interop/qmp-spec.txt |  5 +++--
> >  qapi/misc.json            | 40 ---------------------------------------
> >  2 files changed, 3 insertions(+), 42 deletions(-)
> >
> > diff --git a/docs/interop/qmp-spec.txt b/docs/interop/qmp-spec.txt
> > index 8f7da0245d..67e44a8120 100644
> > --- a/docs/interop/qmp-spec.txt
> > +++ b/docs/interop/qmp-spec.txt
> > @@ -130,8 +130,9 @@ to pass "id" with out-of-band commands.  Passing it with all commands
> >  is recommended for clients that accept capability "oob".
> >  
> >  If the client sends in-band commands faster than the server can
> > -execute them, the server will eventually drop commands to limit the
> > -queue length.  The sever sends event COMMAND_DROPPED then.
> > +execute them, the server will stop reading the requests from the QMP
> > +channel until the request queue length is reduced to an acceptable
> > +range.
> 
> The change described by this documentation update is in the previous
> commit.  This commit merely cleans up unused code.  Instead of moving
> the doc update to the previous commit, we can simply squash the two
> commits.

Sure, I'll squash.

> 
> Let's add a hint on managing flow of in-band commands to keep the
> monitor available for out-of-band commands.  Here's my try:
> 
>     If the client sends in-band commands faster than the server can
>     execute them, the server will stop reading the requests from the QMP
>     channel until its request queue length falls below the limit.  To
>     keep the monitor available for out-of-band commands, the client has
>     to manage the flow of in-band commands.
> 
> Of course, anyone trying to put this hint to use will need to know the
> actual request queue limit.  Options:
> 
> * Make it ABI by documenting it here
> 
> * Let the client configure it with a suitable command
> 
> * Let the introspect it with a suitable command

I'm not sure whether we should expose this information to the client,
considering that the client can after all detect that "full" by
monitoring the status of its output buffer used (e.g., poll with
POLLOUT) and assuming that should be enough for a client.  Or did I
miss anything that you were trying to emphasize but I didn't notice
(since after all you mentioned this too in the other thread)?

Regards,

-- 
Peter Xu