[RFC] qemu: convert DomainLogContext class to use GObject

[Ján Tomko]

On a Wednesday in 2020, Peter Krempa wrote:
>On Tue, Mar 10, 2020 at 17:30:28 +0000, Daniel Berrange wrote:
>> On Tue, Mar 10, 2020 at 06:20:49PM +0100, Ján Tomko wrote:
>> > On a Tuesday in 2020, Gaurav Agrawal wrote:
>> > > ---
>> > > src/qemu/qemu_domain.c  | 36 ++++++++++++++++++++----------------
>> > > src/qemu/qemu_domain.h  |  6 ++++--
>> > > src/qemu/qemu_process.c |  4 ++--
>> > > 3 files changed, 26 insertions(+), 20 deletions(-)
>> > >
>> >
>> > [...]
>> >
>> > > @@ -10632,7 +10635,8 @@ qemuDomainLogContextPtr qemuDomainLogContextNew(virQEMUDriverPtr driver,
>> > >     return ctxt;
>> > >
>> > >  error:
>> > > -    virObjectUnref(ctxt);
>> > > +    if (ctxt)
>> > > +        g_object_unref(ctxt);
>> >
>> > g_object_unref is safe to call with a NULL argument, the "if (ctxt)"
>> > check is not needed here.
>>
>> I'm not so sure on that.
>>

The code itself does check for NULL, it's hidden in the
   g_return_if_fail (G_IS_OBJECT (object));
call which boils down to
   g_type_check_instance_is_fundamentally_a

Even though the documentation does not mention NULL is safe, it has to be, since it's
used as a cleanup function in gobject/gobject-autocleanups.h

>> g_clear_object API docs explicitly say that it is OK if the object is NULL:
>>
>>    https://developer.gnome.org/gobject/stable/gobject-The-Base-Object-Type.html#g-clear-object
>
>I'd prefer we agree on using this one globally on the same basis we had
>for using VIR_FREE even on cleanup paths.

Sounds good. Most of the unrefs will be handled by g_auto anyway.

Jano
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