Re: [Qemu-devel] [PATCH v4 04/14] pc: prepare for multi stage hotplug handlers

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 30 May 2018 16:13:32 +0200
David Hildenbrand <david@redhat.com> wrote:

> On 30.05.2018 15:08, Igor Mammedov wrote:
> > On Thu, 17 May 2018 10:15:17 +0200
> > David Hildenbrand <david@redhat.com> wrote:
> >   
> >> For multi stage hotplug handlers, we'll have to do some error handling
> >> in some hotplug functions, so let's use a local error variable (except
> >> for unplug requests).  
> > I'd split out introducing local error into separate patch
> > so patch would do a single thing.
> >   
> >> Also, add code to pass control to the final stage hotplug handler at the
> >> parent bus.  
> > But I don't agree with generic
> >  "} else if ("dev->parent_bus && dev->parent_bus->hotplug_handler) {"
> > forwarding, it's done by 3/14 for generic case and in case of
> > special device that needs bus handler called from machine one,
> > I'd suggest to do forwarding explicitly for that device only
> > like we do with acpi_dev.  
> 
> I decided to do it that way because it is generic and results in nicer
> recovery handling (e.g. in case pc_dimm plug fails, we can simply
> rollback all (for now MemoryDevice) previous plug operations).
rollback should be managed by the caller of pc_dimm plug
directly, so it's not relevant here.

> IMHO, the resulting code is easier to read.
> 
> From this handling it is clear that
> "if we reach the hotplug handler, and it is not some special device
> plugged by the machine (CPU, PC_DIMM), pass it on to the actual hotplug
> handler if any exists"
I strongly disagree with that it's easier to deal with.
You are basically duplicating already generalized code
from qdev_get_hotplug_handler() back into boards.

If a device doesn't have to be handled by machine handler,
than qdev_get_hotplug_handler() must return its bus handler
if any directly. So branch in question that your are copying
is a dead one, pls drop it.


> 
> > 
> >   
> >> Signed-off-by: David Hildenbrand <david@redhat.com>
> >> ---
> >>  hw/i386/pc.c | 39 +++++++++++++++++++++++++++++++--------
> >>  1 file changed, 31 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> >> index d768930d02..510076e156 100644
> >> --- a/hw/i386/pc.c
> >> +++ b/hw/i386/pc.c
> >> @@ -2007,19 +2007,32 @@ static void pc_cpu_pre_plug(HotplugHandler *hotplug_dev,
> >>  static void pc_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
> >>                                            DeviceState *dev, Error **errp)
> >>  {
> >> +    Error *local_err = NULL;
> >> +
> >> +    /* final stage hotplug handler */
> >>      if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> >> -        pc_cpu_pre_plug(hotplug_dev, dev, errp);
> >> +        pc_cpu_pre_plug(hotplug_dev, dev, &local_err);
> >> +    } else if (dev->parent_bus && dev->parent_bus->hotplug_handler) {
> >> +        hotplug_handler_pre_plug(dev->parent_bus->hotplug_handler, dev,
> >> +                                 &local_err);
> >>      }
> >> +    error_propagate(errp, local_err);
> >>  }
> >>  
> >>  static void pc_machine_device_plug_cb(HotplugHandler *hotplug_dev,
> >>                                        DeviceState *dev, Error **errp)
> >>  {
> >> +    Error *local_err = NULL;
> >> +
> >> +    /* final stage hotplug handler */
> >>      if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
> >> -        pc_dimm_plug(hotplug_dev, dev, errp);
> >> +        pc_dimm_plug(hotplug_dev, dev, &local_err);
> >>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> >> -        pc_cpu_plug(hotplug_dev, dev, errp);
> >> +        pc_cpu_plug(hotplug_dev, dev, &local_err);
> >> +    } else if (dev->parent_bus && dev->parent_bus->hotplug_handler) {
> >> +        hotplug_handler_plug(dev->parent_bus->hotplug_handler, dev, &local_err);
> >>      }
> >> +    error_propagate(errp, local_err);
> >>  }
> >>  
> >>  static void pc_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
> >> @@ -2029,7 +2042,10 @@ static void pc_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
> >>          pc_dimm_unplug_request(hotplug_dev, dev, errp);
> >>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> >>          pc_cpu_unplug_request_cb(hotplug_dev, dev, errp);
> >> -    } else {
> >> +    } else if (dev->parent_bus && dev->parent_bus->hotplug_handler) {
> >> +        hotplug_handler_unplug_request(dev->parent_bus->hotplug_handler, dev,
> >> +                                       errp);
> >> +    } else if (!dev->parent_bus) {
> >>          error_setg(errp, "acpi: device unplug request for not supported device"
> >>                     " type: %s", object_get_typename(OBJECT(dev)));
> >>      }
> >> @@ -2038,14 +2054,21 @@ static void pc_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
> >>  static void pc_machine_device_unplug_cb(HotplugHandler *hotplug_dev,
> >>                                          DeviceState *dev, Error **errp)
> >>  {
> >> +    Error *local_err = NULL;
> >> +
> >> +    /* final stage hotplug handler */
> >>      if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
> >> -        pc_dimm_unplug(hotplug_dev, dev, errp);
> >> +        pc_dimm_unplug(hotplug_dev, dev, &local_err);
> >>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> >> -        pc_cpu_unplug_cb(hotplug_dev, dev, errp);
> >> -    } else {
> >> -        error_setg(errp, "acpi: device unplug for not supported device"
> >> +        pc_cpu_unplug_cb(hotplug_dev, dev, &local_err);
> >> +    } else if (dev->parent_bus && dev->parent_bus->hotplug_handler) {
> >> +        hotplug_handler_unplug(dev->parent_bus->hotplug_handler, dev,
> >> +                               &local_err);
> >> +    } else if (!dev->parent_bus) {
> >> +        error_setg(&local_err, "acpi: device unplug for not supported device"
> >>                     " type: %s", object_get_typename(OBJECT(dev)));
> >>      }
> >> +    error_propagate(errp, local_err);
> >>  }
> >>  
> >>  static HotplugHandler *pc_get_hotpug_handler(MachineState *machine,  
> >   
> 
>