linux-kernel - Re: [PATCH v4 1/4] powerpc: make llseek 32bit-only.

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Date:   Thu, 29 Aug 2019 14:57:39 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Michal Suchánek <msuchanek@...e.de>
Cc:     David Hildenbrand <david@...hat.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        David Howells <dhowells@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        Breno Leitao <leitao@...ian.org>,
        Michael Neuling <mikey@...ling.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Allison Randal <allison@...utok.net>,
        Firoz Khan <firoz.khan@...aro.org>,
        Joel Stanley <joel@....id.au>,
        Nicolai Stange <nstange@...e.de>,
        Nicholas Piggin <npiggin@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christian Brauner <christian@...uner.io>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v4 1/4] powerpc: make llseek 32bit-only.

On Thu, Aug 29, 2019 at 2:37 PM Michal Suchánek <msuchanek@...e.de> wrote:
> On Thu, 29 Aug 2019 14:19:46 +0200 Arnd Bergmann <arnd@...db.de> wrote:
> > On Thu, Aug 29, 2019 at 12:23 PM Michal Suchanek <msuchanek@...e.de> wrote:
> > In particular, I don't see why you single out llseek here, but leave other
> > syscalls that are not needed on 64-bit machines such as pread64().
>
> Because llseek is not built in fs/ when building 64bit only causing a
> link error.
>
> I initially posted patch to build it always but it was pointed out it
> is not needed, and  the interface does not make sense on 64bit, and
> that platforms that don't have it on 64bit now don't want that useless
> code.

Ok, please put that into the changeset description then.

I looked at uses of __NR__llseek in debian code search and
found this one:

https://codesearch.debian.net/show?file=umview_0.8.2-1.2%2Fxmview%2Fum_mmap.c&line=328

It looks like this application will try to use llseek instead of lseek
when built against kernel headers that define __NR_llseek.

Changing the powerpc kernel not to provide that to user
space may break it unless the program gets recompiled against
the latest headers.

      Arnd