Re: [Qemu-devel] Re: [PATCH v2 3/3] char: emit the OPENED event only when a new char connection is opened

[Amit Shah]

On (Mon) Oct 26 2009 [21:15:57], Jan Kiszka wrote:
> >>> However, with the qcow2 synchronous patch, the monitor prompt doesn't
> >>> come up again -- which shows there is a problem with the way the bhs
> >>> work and also the initial resets.
> >> Then the qcow2 patch is already in? At least applying your patch doesn't
> >> change the picture.
> > 
> > Yeah; that patch went in just before my patches. Can you try reverting
> > 
> > ef845c3bf421290153154635dc18eaa677cecb43
> 
> Makes no difference either - but it also does not touch any code that
> code impact the open/reset signaling.

What happens is the BHs that are run get run in a different order.

Let me explain the two scenarios:

1. Current qemu tree, plus my patch to fix this issue that's in
Anthony's queue plus reverting the qcow2 patch -- the monitor prompt
appears fine.

2. Current qemu tree plus my patch from Anthony's queue - the monitor
prompt doesn't appear.

The difference is in the order the BHs are scheduled. In the case
without the qcow2 patch, the bhs get scheduled early on and results in
initial_reset_issued getting set. Later, when the char devs are
initialsed, the OPENED event is sent out.

In the case with the qcow2 patch, the bhs are run in a different order
-- the bhs are scheduled but not run, and when the char init happens,
the condition

if (s->bh == NULL)

is false and the bhs in effect get scheduled only once, not emitting the
opened event.

Of course, the qcow2 patch just causes some conditions for the bh
handling to happen differently which I've not examined yet. I just
tracked why this was happening.

All that said, I'm ok with reverting that patch now till I find some
kind of a solution to this.

                Amit