On Jun 11, 2019, at 3:09 PM, Andrew Morton [off-list ref] wrote:

On Tue, 11 Jun 2019 15:00:10 -0600 Andreas Dilger [off-list ref] wrote:

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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.

quoted

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().

The real question is whether we want to live with a sub-standard macro for
the next 20 years rather than taking the opportunity to clean it up now?

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?

Cheers, Andreas