Re: [Qemu-devel] [RFC PATCH 6/6] pc: Support firmware configuration with -blockdev

[Markus Armbruster]

Laszlo Ersek <address@hidden> writes:

> On 03/04/19 18:50, Markus Armbruster wrote:
>
>> Alright, we can call object_get_class(dev_obj)->unparent(dev_obj).
>> 
>> Final complication: if I call just that, the device's reference counter
>> goes down to zero in the middle of device_unparent(), and we use after
>> free.  So I bracket he call with object_ref() and object_unref().
>
> I don't think that requiring such a bracketing is necessarily a problem.
> I vaguely remember reviewing a kernel patch 6 or so years ago where the
> patch used the same idea, with those "get" and "put" functions (the bug
> the patch was fixing was that the last reference was "temporarily" lost
> mid-operation).

I don't regard it as problem.  My voodoo coding just wasn't prepared for
it.

> So perhaps this can be addressed, for the general case, by extending the
> documentation of device_unparent(). (The function has no documentation
> at all, at the moment.)

I know just enough to be dangerous here, not enough to write
documentation.

We really need a complete life cycle diagram for devices.  The closest
we have is the section on realization in qdev-core.h, which lets me
divine only a part of the life cycle.  The missing part I struggled with
here is how to go from device state "created, not realized" to
"destroyed".