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

From: "Michal Suchánek" <msuchanek@suse.de>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Michael Neuling <mikey@neuling.org>,
	Andrew Donnellan <andrew.donnellan@au1.ibm.com>,
	Nicolai Stange <nstange@suse.de>,
	David Hildenbrand <david@redhat.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Nicholas Piggin <npiggin@gmail.com>,
	David Howells <dhowells@redhat.com>,
	Hari Bathini <hbathini@linux.ibm.com>,
	Paul Mackerras <paulus@samba.org>, Joel Stanley <joel@jms.id.au>,
	Christian Brauner <christian@brauner.io>,
	Firoz Khan <firoz.khan@linaro.org>,
	Breno Leitao <leitao@debian.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Allison Randal <allison@lohutok.net>,
	"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH v4 1/4] powerpc: make llseek 32bit-only.
Date: Thu, 29 Aug 2019 16:19:23 +0200	[thread overview]
Message-ID: <20190829161923.101ff3eb@kitsune.suse.cz> (raw)
In-Reply-To: <CAK8P3a2DHP+8Vbc4yjq5-wT9GpSxvndCa8gnvx0WcD8YAUAsMw@mail.gmail.com>

On Thu, 29 Aug 2019 14:57:39 +0200
Arnd Bergmann <arnd@arndb.de> wrote:

> On Thu, Aug 29, 2019 at 2:37 PM Michal Suchánek <msuchanek@suse.de> wrote:
> > On Thu, 29 Aug 2019 14:19:46 +0200 Arnd Bergmann <arnd@arndb.de> wrote:  
> > > On Thu, Aug 29, 2019 at 12:23 PM Michal Suchanek <msuchanek@suse.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.
> 

The available documentation says this syscall is for 32bit only so
using it on 64bit is undefined. The interface is not well-defined in
that case either.

Thanks

Michal