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Date: Tue, 11 Jun 2019 14:09:07 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Andreas Dilger <adilger@...ger.ca>
Cc: Shyam Saini <shyam.saini@...rulasolutions.com>,
kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
keescook@...omium.org, linux-arm-kernel@...ts.infradead.org,
linux-mips@...r.kernel.org, intel-gvt-dev@...ts.freedesktop.org,
intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
netdev@...r.kernel.org, linux-ext4 <linux-ext4@...r.kernel.org>,
devel@...ts.orangefs.org, linux-mm@...ck.org, linux-sctp@...r.kernel.org,
bpf@...r.kernel.org, kvm@...r.kernel.org, mayhs11saini@...il.com, Alexey
Dobriyan <adobriyan@...il.com>
Subject: Re: [PATCH V2] include: linux: Regularise the use of FIELD_SIZEOF
macro
On Tue, 11 Jun 2019 15:00:10 -0600 Andreas Dilger <adilger@...ger.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?
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