Re: [Qemu-devel] [PATCH] qdev: Make "hotplugged" property read-only

[Eduardo Habkost <ehabkost@redhat.com>]

(CCing libvir-list and Laine)

On Tue, Jan 03, 2017 at 05:53:27PM +0100, Igor Mammedov wrote:
> On Tue, 3 Jan 2017 17:10:15 +0100
> Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
> > 
> > 
> > On 03/01/2017 15:22, Eduardo Habkost wrote:
> > >> I didn't know that. Is this documented somewhere?
> > >> Is it actually used by any existing software?
> > > not that I know of. But users should be fixed if they are not using it.
> > > 
> > > I see. The problem is that the mechanism is undocumented,
> > > untested, and seems very likely to trigger bugs in device code.
> > 
> > I agree.  Why can't hotplugged be migrated?
> It's probably not migrated because of it's not runtime/guest modified
> state so we don't have to migrate it as it's know in advance.
> 
> For now it should set manually on CLI (-device) with the rest of
> hotplugged device properties.

As this recommendation has the potential to trigger hidden bugs
(and known to trigger a bug in QEMU <= 2.8), I would like it to
be properly documented, and the documentation/recommendations
reviewed following the usual patch review process.

While we don't do that, setting "hotplugged=true" on the
command-line is an unused, undocumented, untested (and
unsupported?) feature.

-- 
Eduardo