Re: [Qemu-devel] [RFC PATCH] qdev: Mark devices as non-hotpluggable by default

[Thomas Huth]

On 21.09.2017 20:50, Eduardo Habkost wrote:
> On Tue, Sep 19, 2017 at 10:55:53AM +0200, Thomas Huth wrote:
>> Historically we've marked all devices as hotpluggable by default. However,
>> most devices are not hotpluggable, and you also need a HotplugHandler to
>> support these devices. So if the user tries to "device_add" or "device_del"
>> such a non-hotpluggable device during runtime, either nothing really usable
>> happens, or QEMU even crashes/aborts unexpectedly (see for example commit
>> 84ebd3e8c7d4fe955b - "Mark diag288 watchdog as non-hotpluggable").
>> So let's change this dangerous default behaviour and mark the devices as
>> non-hotpluggable by default. Certain parent devices classes which are known
>> as hotpluggable (e.g. PCI, USB, etc.) are marked with "hotpluggable = true",
>> so that devices that are derived from these classes continue to work as
>> expected.
> 
> These seem to be missing:
> * TYPE_CPU (or at least TYPE_X86_CPU and TYPE_S390_CPU)
> * TYPE_VIRTIO_SERIAL_PORT
> * TYPE_CCID_CARD
> * TYPE_XENSYSDEV

Thanks for the detailed examination, Eduardo! I'll rework my patch
accordingly...

> Also, I don't think we need to set it for TYPE_CPU_CORE, just for
> TYPE_SPAPR_CPU_CORE.

Ok - you're likely right. There is one other consumer of TYPE_CPU_CORE
beside spapr, which is the pnv machine, and as far as I can see, it does
not support CPU hotplugging yet. So it indeed makes more sense to set
this in TYPE_SPAPR_CPU_CORE only.

 Thomas