Re: [Qemu-devel] [PATCH v1 1/2] qdev-monitor.c: Register reset function if the device has one

[Markus Armbruster <armbru@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 18/02/2016 10:56, Markus Armbruster wrote:
>> Alistair Francis <alistair.francis@xilinx.com> writes:
>> 
>>> If the device being added when running qdev_device_add() has
>>> a reset function, register it so that it can be called.
>>>
>>> Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
>>> ---
>>>
>>>  qdev-monitor.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/qdev-monitor.c b/qdev-monitor.c
>>> index 81e3ff3..0a99d01 100644
>>> --- a/qdev-monitor.c
>>> +++ b/qdev-monitor.c
>>> @@ -561,6 +561,8 @@ DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
>>>  
>>>      if (bus) {
>>>          qdev_set_parent_bus(dev, bus);
>>> +    } else if (dc->reset) {
>>> +        qemu_register_reset((void (*)(void *))dc->reset, dev);
>>>      }
>>>  
>>>      id = qemu_opts_id(opts);
>> 
>> This looks wrong to me.
>> 
>> You stuff all the device reset methods into the global reset_handlers
>> list, where they get called in some semi-random order.  This breaks when
>> there are reset order dependencies between devices, e.g. between a
>> device and the bus it plugs into.
>
> There is no bus here, see the "if" above the one that's being added.
>
> However, what devices have done so far is to register/unregister the
> reset in the realize/unrealize methods, and I suggest doing the same.

Shows that our support for bus-less devices is still in its infancy.

For me, a device has a number of external connectors that need to be
wired up.  A qdev bus is merely a standardized package of such
connectors.  For historical reasons, buses are all qdev has, with a
special sysbus for everything that cannot be shoehorned into a single
bus.  To work with individual connectors, you have to drop into C
(ignoring the weird "platform bus" sysbus thing Alex added).  Support
for doing that at configuration rather than code level would be nice.

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