Re: [Qemu-devel] [RESEND PATCH 1/2] qdev: Track runtime machine modifications

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 2011-01-12 at 13:09 +0100, Markus Armbruster wrote:
> Alex Williamson <alex.williamson@redhat.com> writes:
> 
> > Create a trivial interface to track whether the machine has been
> > modified since boot.  Adding or removing devices will trigger this
> > to return true.  An example usage scenario for such an interface is
> > the rtl8139 driver which includes a cpu_register_io_memory() value
> > in it's migration stream.  For the majority of migrations, where
> > no hotplug has occured in the machine, this works correctly.  Once
> > the machine is modified, we can use this interface to detect that
> > and include a subsection for the device to prevent migrations to
> > rtl8139 versions with this bug.
> >
> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> > Acked-by: Michael S. Tsirkin <mst@redhat.com>
> > Acked-by: Juan Quintela <quintela@redhat.com>
> > ---
> >
> >  hw/qdev.c |   10 ++++++++++
> >  hw/qdev.h |    1 +
> >  2 files changed, 11 insertions(+), 0 deletions(-)
> >
> > diff --git a/hw/qdev.c b/hw/qdev.c
> > index 6fc9b02..e450c21 100644
> > --- a/hw/qdev.c
> > +++ b/hw/qdev.c
> > @@ -32,6 +32,8 @@
> >  #include "blockdev.h"
> >  
> >  static int qdev_hotplug = 0;
> > +static bool qdev_hot_added = false;
> > +static bool qdev_hot_removed = false;
> >  
> >  /* This is a nasty hack to allow passing a NULL bus to qdev_create.  */
> >  static BusState *main_system_bus;
> > @@ -93,6 +95,7 @@ static DeviceState *qdev_create_from_info(BusState *bus, DeviceInfo *info)
> >      if (qdev_hotplug) {
> >          assert(bus->allow_hotplug);
> >          dev->hotplugged = 1;
> > +        qdev_hot_added = true;
> >      }
> >      dev->instance_id_alias = -1;
> >      dev->state = DEV_STATE_CREATED;
> > @@ -294,6 +297,8 @@ int qdev_unplug(DeviceState *dev)
> >      }
> >      assert(dev->info->unplug != NULL);
> >  
> > +    qdev_hot_removed = true;
> > +
> >      return dev->info->unplug(dev);
> >  }
> >  
> > @@ -394,6 +399,11 @@ void qdev_machine_creation_done(void)
> >      qdev_hotplug = 1;
> >  }
> >  
> > +bool qdev_machine_modified(void)
> > +{
> > +    return qdev_hot_added || qdev_hot_removed;
> > +}
> > +
> >  /* Get a character (serial) device interface.  */
> >  CharDriverState *qdev_init_chardev(DeviceState *dev)
> >  {
> 
> Why do you track add/remove separately, in qdev_hot_added and
> qdev_hot_removed?  I don't mind, just curious.

I thought the distinction might be useful at some point, but we don't
use it yet.  Thanks,

Alex