linux-kernel - Re: [PATCH] Install kernel-page-flags.h

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Message-ID: <CACVxJT_4Lp3FYjsE_-pW_E3pT-hd5ARF0_2qMMJo5ooT3Y_WfA@mail.gmail.com>
Date:	Mon, 19 Mar 2012 14:45:36 +0200
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Ulrich Drepper <drepper@...adia.org>, arnd@...db.de,
	davem@...emloft.net, hverkuil@...all.nl,
	laurent.pinchart@...asonboard.com, linux-kernel@...r.kernel.org,
	mchehab@...hat.com
Subject: Re: [PATCH] Install kernel-page-flags.h

On Mon, Mar 19, 2012 at 2:32 PM, Christoph Hellwig <hch@...radead.org> wrote:
> On Wed, Mar 14, 2012 at 12:40:36PM +0200, Alexey Dobriyan wrote:
>> >> Programs using /proc/kpageflags need to know about the various flags. ??The
>> >> <linux/kernel-page-flags.h> provides them and the comments in the file
>> >> indicate that it is supposed to be used by user-level code. ??But the file
>> >> is not installed.
>> >>
>> >> The patch below installs the headers and marks the unstable flags as
>> >> out-of-bounds.
>> >
>> > I don't think this is a good idea at all. ??Let's shoot the person who
>> > added that braindead interface ASAP, and replace it with one printing
>> > the flags in ASCII format.
>>
>> ASCII sucks.
>> This interface is not for humans.
>
> But we still can't lock down the page flags for a user interface - they
> are a very scare resource and we can't afford to keep them stable due
> to userspace poking into internals.
>
> I guess the best we can do is to have a translation table for kernel
> internal to external documented flags.  Once you export the header with
> the meanings it's time to add that table, even if it starts out as a 1:1
> mapping.

Well, this is totally different issue.
Translation is already there, see stable_page_flags().
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