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Date: Sun, 17 Dec 2023 00:18:17 +0000
From: Matthew Wilcox <willy@infradead.org>
To: Randy Dunlap <rdunlap@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, tglx@linutronix.de, x86@kernel.org,
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	dave.hansen@linux.intel.com, mingo@redhat.com, will@kernel.org,
	longman@redhat.com, boqun.feng@gmail.com, brauner@kernel.org
Subject: Re: [PATCH 46/50] preempt.h: Kill dependency on list.h
Message-ID: <ZX4+STzh5MFhVHrw@casper.infradead.org>
References: <20231216024834.3510073-1-kent.overstreet@linux.dev>
 <20231216033552.3553579-1-kent.overstreet@linux.dev>
 <20231216033552.3553579-3-kent.overstreet@linux.dev>
 <ZX1AFVAWXMfbo+Ry@casper.infradead.org>
 <20231216223522.s4skrclervsskx32@moria.home.lan>
 <82ed43c2-2a9d-4c5e-8ccd-8078397b7953@infradead.org>
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In-Reply-To: <82ed43c2-2a9d-4c5e-8ccd-8078397b7953@infradead.org>

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.