linux-kernel - Re: [RFC][PATCH 1/5] pagemap: remove file header

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Date:	Tue, 7 Aug 2007 22:51:21 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Dave Hansen <haveblue@...ibm.com>, linux-kernel@...r.kernel.org,
	serue@...ibm.com
Subject: Re: [RFC][PATCH 1/5] pagemap: remove file header

On Wed, Aug 08, 2007 at 02:31:00AM +0100, Alan Cox wrote:
> O> > The endianness is only useful when examining a raw dump of
> > > pagemap from a different machine when you don't know the
> > > source of the file.  This is pretty rare, and the programs
> > > or scripts doing the copying off-machine can certainly be
> > > made to hold this information.
> 
> Nobody fancies doing bi-endian MIPS ?

Indeed not.
 
> > > The page size is available in userspace at least with libc's
> > > getpagesize().  This will also never vary across processes,
> 
> For now. Its a logical direction however thant we end up with bigger page
> sizes either by hardware or by software merging and end up having
> different page sizes for legacy 32bit binaries.

Blerch.

> > I'd really strongly prefer to have no header. It was added to
> > futureproof the thing.
> 
> The information needed to parse /proc/pid/pagemap can be stuck
> in /proc/pid/somewherelese. If we ever get page size variations and the
> like then /proc/pid/ is going to end up with that information anyway for
> ps and friends to use.

Well if somewhereelse doesn't exist today, programs written today will
break on tomorrow's kernels.

-- 
Mathematics is the supreme nostalgia of our time.
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