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

[Michal SuchÃnek]

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

> On Thu, Aug 29, 2019 at 2:37 PM Michal SuchÃnek <msuchanek@xxxxxxx> wrote:
> > On Thu, 29 Aug 2019 14:19:46 +0200 Arnd Bergmann <arnd@xxxxxxxx> wrote:  
> > > On Thu, Aug 29, 2019 at 12:23 PM Michal Suchanek <msuchanek@xxxxxxx> 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