linux-kernel - Re: [RFCLUE3] flagging kernel interface changes

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Date:	Sun, 21 Jan 2007 11:15:45 -0800
From:	William D Waddington <william.waddington@...zmo.com>
To:	Jesper Juhl <jesper.juhl@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [RFCLUE3] flagging kernel interface changes

Jesper Juhl wrote:
> On 15/11/06, William D Waddington <william.waddington@...zmo.com> wrote:
> 
>> I tried submitting a patch a while back:
>> "[PATCH] IRQ: ease out-of-tree migration to new irq_handler prototype"
>> to add #define __PT_REGS to include/linux/interrupt.h to flag the change
>> to the new interrupt handler prototype.  It wasn't well received :(
>>
>> No big surprise.  The #define wasn't my idea and I hadn't submitted a
>> patch before.  I wanted to see how the patch procedure worked, and
>> hoped that the flag would be included so I could mod my drivers and
>> move on...
>>
>> What I'm curious about is why flagging kernel/driver interface changes
>> is considered a bad idea.  From my point of view as a low-life out-of-
>> tree driver maintainer,
>>
>> #ifdef NEW_INTERFACE
>> #define <my new internals>
>> #endif
>>
>> (w/maybe an #else...)
>>
>> is cleaner and safer than trying to track specific kernel versions in
>> a multi-kernel-version driver.  It seems that in some cases, the new
>> interface has been, like HAVE_COMPAT_IOCTL for instance.
>>
>> I don't want to start an argument about "stable_api_nonsense" or the
>> wisdom of out-of-tree drivers.  Just curious about the - why - and
>> whether it is indifference or antagonism toward drivers outside the
>> fold. Or ???
>>
> 
> I would say that one reason is that cluttering up the kernel with
> #ifdef's is ugly and annoying to maintain long-term. Especially when
> it's expected that anyone who changes in-kernel interfaces also fix up
> any user(s) of those interfaces, so the #ifdef's are pointless
> (ignoring out-of-tree code that is).

Ah, but out-of-tree code is what I'm stuck w/maintaining.  I wouldn't
want to infest in-tree drivers w/#ifdef's either, but they are a fact
of life in my world.  And, lately, _really_ ugly version tests.

If I had _my_ way, there would be a kernel_interface_change.h file that
had an #define'd entry for _every_ kernel interface change within a
major release series:

/*
  * include/linux/interrupt.h interface change x.y.z
  * interrupt handler now takes 2 args
  */
#define INTERRUPT_H_CHANGE_X.Y.Z "interrupt handler now takes 2 args"

or something.

I understand that many (most?) kernel maintainers would prefer that
all drivers be brought in-tree, and aren't particularly concerned
when interface changes affect out-of-tree drivers.

Respectfully, I suggest that world domination isn't quite the same
thing as world dictatorship, and maybe the road to the former would
be helped by a little less of the latter :)

Rat-bastard out-of-tree maintainer takes refuge under desk....

Thanks,
Bill
-- 
--------------------------------------------
William D Waddington
Bainbridge Island, WA, USA
william.waddington@...zmo.com
--------------------------------------------
"Even bugs...are unexpected signposts on
the long road of creativity..." - Ken Burtch
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