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

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Date:	Mon, 19 Mar 2012 07:32:41 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	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 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.
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