Re: [PATCH v2 3/8] qnum: QNumValue type for QNum value literals

[Eduardo Habkost]

On Tue, Nov 24, 2020 at 04:20:37PM +0100, Markus Armbruster wrote:
> Eduardo Habkost <ehabkost@redhat.com> writes:
> 
> > On Tue, Nov 24, 2020 at 09:49:30AM +0100, Markus Armbruster wrote:
> >> Eduardo Habkost <ehabkost@redhat.com> writes:
> >> 
> >> > On Mon, Nov 23, 2020 at 08:51:27AM +0100, Markus Armbruster wrote:
> >> >> Eduardo Habkost <ehabkost@redhat.com> writes:
> >> >> 
> >> >> > On Fri, Nov 20, 2020 at 06:29:16AM +0100, Markus Armbruster wrote:
> >> >> [...]
> >> >> >> When the structure of a data type is to be kept away from its users, 
> >> >> >> I
> >> >> >> prefer to keep it out of the public header, so the compiler enforces 
> >> >> >> the
> >> >> >> encapsulation.
> >> >> >
> >> >> > I prefer that too, except that it is impossible when users of the
> >> >> > API need the compiler to know the struct size.
> >> >> 
> >> >> There are cases where the structure of a data type should be
> >> >> encapsulated, yet its size must be made known for performance (avoid
> >> >> dynamic memory allocation and pointer chasing).
> >> >> 
> >> >> Need for encapsulation correlates with complex algorithms and data
> >> >> structures.  The cost of dynamic allocation is often in the noise then.
> >> >
> >> > I don't know what we are talking about anymore.  None of this
> >> > applies to the QNum API, right?
> >> >
> >> > QNum/QNumValue are not complex data structures, and the reason we
> >> > need the compiler to know the size of QNumValue is not related to
> >> > performance at all.
> >> 
> >> We started with the question whether to make QNumValue's members
> >> private.  We digressed to the question when to make members private.
> >> So back to the original question.
> >> 
> >> > We might still want to discourage users of the QNum API from
> >> > accessing QNum.u/QNumValue.u directly.  Documenting the field as
> >> > private is a very easy way to do it.
> >> 
> >> It's a complete non-issue.  QNum has been around for years, and we
> >> haven't had any issues that could've been plausibly avoided by asking
> >> people to refrain from accessing its members.
> >> 
> >> If there was an actual need to keep the members private, I'd move the
> >> struct out of the header, so the compiler enforces privacy.
> >
> > Understood.  There's still a question I'd like to answer, to
> > decide how the API documentation should look like:
> >
> >   Is QNum.u/QNumValue.u required to be part of the API
> >   documentation?
> >
> > If accessing that field directly is not necessary for using the
> > API, I don't think it should appear in the documentation (because
> > it would be just noise).
> 
> The current patch's comment on QNumValue looks good to me.
> 
> Does this answer your question?

The current patch (v3) doesn't address the question.  It doesn't
include documentation for the field, but doesn't hide it.
kernel-doc will print a warning on that case.

-- 
Eduardo