Re: [Qemu-devel] [PATCH v6 21/25] replay: replay BH for IDE trim operation

[Pavel Dovgalyuk]

> From: Pavel Dovgalyuk [mailto:address@hidden
> > From: John Snow [mailto:address@hidden
> > On 09/12/2018 04:19 AM, Pavel Dovgalyuk wrote:
> > > This patch makes IDE trim BH deterministic, because it affects
> > > the device state. Therefore its invocation should be replayed
> > > instead of running at the random moment.
> > >
> > > Signed-off-by: Pavel Dovgalyuk <address@hidden>
> > > Reviewed-by: Paolo Bonzini <address@hidden>
> > > ---
> > >  hw/ide/core.c |    3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/hw/ide/core.c b/hw/ide/core.c
> > > index 2c62efc..04e22e7 100644
> > > --- a/hw/ide/core.c
> > > +++ b/hw/ide/core.c
> > > @@ -35,6 +35,7 @@
> > >  #include "sysemu/block-backend.h"
> > >  #include "qapi/error.h"
> > >  #include "qemu/cutils.h"
> > > +#include "sysemu/replay.h"
> > >
> > >  #include "hw/ide/internal.h"
> > >  #include "trace.h"
> > > @@ -479,7 +480,7 @@ static void ide_issue_trim_cb(void *opaque, int ret)
> > >  done:
> > >      iocb->aiocb = NULL;
> > >      if (iocb->bh) {
> > > -        qemu_bh_schedule(iocb->bh);
> > > +        replay_bh_schedule_event(iocb->bh);
> > >      }
> > >  }
> > >
> > Just passing by: Why do we need to change this call, but nothing else in
> > IDE?
> 
> This call is responsible for a bug that was reproducible.
> 
> > I don't mind conceptually, but it's odd to me that of all the calls I
> > make in this emulator that change state somewhere that this is the only
> > one you need to hijack for the replay feature.
> >
> > Is this a necessarily complete change?


I found one more BH in ide/core:

static void ide_restart_cb(void *opaque, int running, RunState state)
{
    IDEBus *bus = opaque;

    if (!running)
        return;

    if (!bus->bh) {
        bus->bh = qemu_bh_new(ide_restart_bh, bus);
        qemu_bh_schedule(bus->bh);
    }
}

void ide_register_restart_cb(IDEBus *bus)
{
    if (bus->dma->ops->restart_dma) {
        bus->vmstate = qemu_add_vm_change_state_handler(ide_restart_cb, bus);
    }
}

As I understand, it is called when VM start/stop event happen.
These events are not related to the guest state.

Does this BH change the guest state somehow?

Pavel Dovgalyuk