[PATCH V2] include: linux: Regularise the use of FIELD_SIZEOF macro

[Andrew Morton]

On Tue, 11 Jun 2019 15:00:10 -0600 Andreas Dilger <adilger at dilger.ca> wrote:

> >> to FIELD_SIZEOF
> > 
> > As Alexey has pointed out, C structs and unions don't have fields -
> > they have members.  So this is an opportunity to switch everything to
> > a new member_sizeof().
> > 
> > What do people think of that and how does this impact the patch footprint?
> 
> I did a check, and FIELD_SIZEOF() is used about 350x, while sizeof_field()
> is about 30x, and SIZEOF_FIELD() is only about 5x.

Erk.  Sorry, I should have grepped.

> That said, I'm much more in favour of "sizeof_field()" or "sizeof_member()"
> than FIELD_SIZEOF().  Not only does that better match "offsetof()", with
> which it is closely related, but is also closer to the original "sizeof()".
> 
> Since this is a rather trivial change, it can be split into a number of
> patches to get approval/landing via subsystem maintainers, and there is no
> huge urgency to remove the original macros until the users are gone.  It
> would make sense to remove SIZEOF_FIELD() and sizeof_field() quickly so
> they don't gain more users, and the remaining FIELD_SIZEOF() users can be
> whittled away as the patches come through the maintainer trees.

In that case I'd say let's live with FIELD_SIZEOF() and remove
sizeof_field() and SIZEOF_FIELD().

I'm a bit surprised that the FIELD_SIZEOF() definition ends up in
stddef.h rather than in kernel.h where such things are normally
defined.  Why is that?