Re: [SPAM] Re: [PATCH 14/15] spapr: Simplify error handling in spapr_memory_plug()

[Greg Kurz]

On Tue, 15 Sep 2020 13:58:53 +0300
Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:

> 14.09.2020 15:35, Greg Kurz wrote:
> > As recommended in "qapi/error.h", add a bool return value to
> > spapr_add_lmbs() and spapr_add_nvdimm(), and use them instead
> > of local_err in spapr_memory_plug().
> > 
> > Since object_property_get_uint() only returns 0 on failure, use
> > that as well.
> 
> Why are you sure? Can't the property be 0 itself?
> 

Hmmm... I've based this assumption on the header:

 * Returns: the value of the property, converted to an unsigned integer, or 0
 * an error occurs (including when the property value is not an integer).

but looking at the implementation, I don't see any check that
a property cannot be 0 indeed...

It's a bit misleading to mention this in the header though. I
understand that the function should return something, which
should have a some explicitly assigned value to avoid compilers
or static analyzers to yell, but the written contract should be
that the value is _undefined_ IMHO.

In its present form, the only way to know if the property is
valid is to pass a non-NULL errp actually. I'd rather even see
that in the contract, and an assert() in the code.

An alternative would be to convert it to have a bool return
value and get the actual uint result with a pointer argument.

> > 
> > Also call ERRP_GUARD() to be able to check the status of void
> > function pc_dimm_plug() with *errp.
> > 
> 
> 

I'm now hesitating to either check *errp for object_property_get_uint()
too or simply drop this patch...