linux-kernel - Re: [PATCH 1/2] x86: Cleanup TIF value gaps in shift range

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Message-ID: <4CBCBF9D.1060409@zytor.com>
Date:	Mon, 18 Oct 2010 14:43:57 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 1/2] x86: Cleanup TIF value gaps in shift range

On 10/18/2010 02:36 PM, David Rientjes wrote:
> On Mon, 18 Oct 2010, H. Peter Anvin wrote:
> 
>> The problem is that someone exports something as debugging information,
>> then someone else suddenly thinks it's an ABI.  I believe the same
>> complainant in the past has objected to changing of formatting in dmesg,
>> which is equally insane.
>>
> 
> It's not insane if there is no other way to ascertain that information.  
> If it's available through sysfs or debugfs (and, even better, documented 
> as part of the API in Documentation/ABI), then I don't think anyone would 
> object to changing a log message.  But I don't think all log messages 
> should be fair game under some general principle if they are being changed 
> (instead of just extending it) without a compelling reason, such as 
> technically being incorrect in its present form.

YES IT IS.  In fact, it is completely and totally bananas bonkers.

By not pushing for a proper maintainable ABI, you will have an
indefinite forward compatibility problem, and when predictably it
breaks, you'll complain.  This is, however, backwards -- the right thing
would have been to say "I need this, this isn't available, I should add
a maintainable API and push it upstream", and perhaps add log parsing as
a backwards-compatibility solution.

	-hpa

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