From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Kirill A. Shutemov" <kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>
Subject: Re: Regression: Requiring CAP_SYS_ADMIN for /proc/<pid>/pagemap
 causes application-level breakage
Date: Thu, 30 Apr 2015 00:37:44 +0300
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To: Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Cc: Konstantin Khlebnikov <koct9i-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Mark Williamson <mwilliamson-/4lU09Eg6ahx67MzidHQgQC/G2K4zDHf@public.gmane.org>, Mark Seaborn <mseaborn-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>, kernel list <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "Kirill A. Shutemov" <kirill.shutemov-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>, Pavel Emelyanov <xemul-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>, Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Finn Grimwood <fgrimwood-/4lU09Eg6ahx67MzidHQgQC/G2K4zDHf@public.gmane.org>, Daniel James <djames-/4lU09Eg6ahx67MzidHQgQC/G2K4zDHf@public.gmane.org>, Cyrill Gorcunov <gorcunov-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>
List-Id: linux-api@vger.kernel.org

On Wed, Apr 29, 2015 at 02:18:49PM -0700, Linus Torvalds wrote:
> On Wed, Apr 29, 2015 at 2:05 PM, Kirill A. Shutemov
> <kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org> wrote:
> >
> > This sounds too ugly to be exposed it as ABI.
> 
> Oh, pretty it ain't. However, regressions in many ways are worse. If
> it makes it possible to not regress...

One idea is to extend kcmp(2) with KCMP_PAGE. idx1 and idx2 are virtual
addresses in two processes. It returns 0 if addresses points to the same
page and 3 otherwise.

Would it be enough for the use case?

I guess it could be too slow to check one page a time...

Invent new kcmpv(2)? ;)

-- 
 Kirill A. Shutemov