linux-kernel - Re: [PATCH 46/50] preempt.h: Kill dependency on list.h

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Message-ID: <20231217002028.shjg6p7wa2cmtkq2@moria.home.lan>
Date: Sat, 16 Dec 2023 19:20:28 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Matthew Wilcox <willy@...radead.org>
Cc: Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	tglx@...utronix.de, x86@...nel.org, tj@...nel.org,
	peterz@...radead.org, mathieu.desnoyers@...icios.com,
	paulmck@...nel.org, keescook@...omium.org,
	dave.hansen@...ux.intel.com, mingo@...hat.com, will@...nel.org,
	longman@...hat.com, boqun.feng@...il.com, brauner@...nel.org
Subject: Re: [PATCH 46/50] preempt.h: Kill dependency on list.h

On Sun, Dec 17, 2023 at 12:18:17AM +0000, Matthew Wilcox wrote:
> On Sat, Dec 16, 2023 at 04:04:43PM -0800, Randy Dunlap wrote:
> > 
> > 
> > On 12/16/23 14:35, Kent Overstreet wrote:
> > > On Sat, Dec 16, 2023 at 06:13:41AM +0000, Matthew Wilcox wrote:
> > >> On Fri, Dec 15, 2023 at 10:35:47PM -0500, Kent Overstreet wrote:
> > >>> -	INIT_HLIST_NODE(&notifier->link);
> > >>> +	/* INIT_HLIST_NODE() open coded, to avoid dependency on list.h */
> > >>> +	notifier->link.next = NULL;
> > >>> +	notifier->link.pprev = NULL;
> > >>
> > >> Arguably INIT_HLIST_NODE() belongs in types.h -- we already have
> > >> RCUREF_INIT() and ATOMIC_INIT() in there.
> > > 
> > > I think I'd prefer to keep types.h as minimal as possible - as soon as
> > > we start putting non type stuff in there people won't know what the
> > > distinction is and it'll grow.
> > > 
> > > preempt.h is a bit unusual too, normally we'd just split out a _types.h
> > > header there but it's not so easy to split up usefully.
> > > 
> > 
> > I don't feel like I have NAK power, but if I did, I would NAK
> > open coding of INIT_HLIST_HEAD() or anything like it.
> > I would expect some $maintainer to do likewise, but I could be
> > surprised.
> 
> There is another solution here (although I prefer moving INIT_HLIST_HEAD
> into types.h).  The preprocessor allows redefinitions as long as the two
> definitions match exactly.  So you can copy INIT_HLIST_HEAD into
> preempt.h and if the definition ever changes, we'll notice.

I like it.