linux-kernel - Re: [PATCH] Break out types from <linux/list.h> to <linux/list

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Message-ID: <4C2E5598.2090503@tilera.com>
Date:	Fri, 2 Jul 2010 17:09:44 -0400
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Matthew Wilcox <matthew@....cx>
CC:	<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] Break out types from <linux/list.h> to	<linux/list_types.h>.

On 7/2/2010 4:48 PM, Matthew Wilcox wrote:
> On Fri, Jul 02, 2010 at 03:33:52PM -0400, Chris Metcalf wrote:
>   
>> On 7/2/2010 3:19 PM, Matthew Wilcox wrote:
>>     
>>> Why a new header file instead of linux/types.h?
>>>       
>> I was working from analogy to kvm_types.h, mm_types.h, rwlock_types.h,
>> spinlock_types.h.  My impression is that linux/types.h is generally for
>> basic (non-struct) types, with atomic_t/atomic64_t being added as
>> "almost non-struct types", and of course the historical exception of
>> "struct ustat", which has been there since the dawn of time (0.97 anyway).
>>     
> I think list_head, hlist_head and hlist_node qualify as "almost non-struct
> types", don't you?  :-)
>   

I see the smiley, but to reply seriously, the distinction I was making
was that atomic_t is really just an integer type, but with typing magic
to protect it from implicit conversion -- unlike list_head, which really
is a more complex type.

I suppose one could make a kind of "intent of the founders"
constitutional law-type argument suggesting that the presence of "struct
ustat" suggests more complex types are in fact appropriate in
<linux/types.h>.  :-)

> I wouldn't mind seeing kvm_types.h, rwlock_types.h and spinlock_types.h
> merged into types.h, personally.  They're all pretty fundamental kernel
> kind of types.  It's a matter of taste, and I'm not particularly fussed
> one way or the other.
>   

Somehow it's hard to see kvm_ioapic_redirect_entry on a par with size_t :-)

> I just object to the unnecessary creation of tiny files like this.
> Which is how we ended up with atomic_t and atomic64_t in there in the
> first place :-)
>   

In any case, I think this either way is plausible, but in the absence of
more folks weighing in, I think "avoid adding a complex type to
<linux/types.h>" sounds more convincing to me than "avoid adding a new
tiny file", though I certainly do buy the latter argument.

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com

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