Subject: Re: [PATCH iproute2] Fix compilation with kernel headers < 3.4

From: Thomas De Schampheleire <[email-masked]>
Date: Mon, 26 Feb 2018 20:21:34 +0100

On Mon, Feb 26, 2018 at 10:58:10AM -0800, Stephen Hemminger wrote:
> On Mon, 26 Feb 2018 19:51:12 +0100
> Thomas De Schampheleire <[email-masked]> wrote:
> 
> > Since commit 596b1c94aa38e21b7a8c8562e8b61ccb744255d2, iproute2 uses types
> > __kernel_long_t and __kernel_ulong_t but does not provide internal
> > definitions for it.
> > 
> > This means that compilation using kernel headers that are older than 3.4
> > (where these types were added) will fail. This situation may be uncommon for
> > native compilation, but not uncommon for cross compilation where the
> > toolchains may be a bit older.
> > 
> > Provide the necessary types internally if not provided by the kernel
> > headers to fix compilation in such cases.
> > 
> > Signed-off-by: Thomas De Schampheleire <[email-masked]>
> > ---
> >  include/uapi/linux/posix_types.h | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/include/uapi/linux/posix_types.h b/include/uapi/linux/posix_types.h
> > index 9a7a740b..60f3d378 100644
> > --- a/include/uapi/linux/posix_types.h
> > +++ b/include/uapi/linux/posix_types.h
> > @@ -35,4 +35,13 @@ typedef int __kernel_mqd_t;
> >  
> >  #include <asm/posix_types.h>
> >  
> > +/* in case the kernel header asm/posix_types.h is too old (< 3.4) to provide
> > + * __kernel_long_t, provide it here */
> > +#ifndef __kernel_long_t
> > +typedef long		__kernel_long_t;
> > +#endif
> > +#ifndef __kernel_ulong_t
> > +typedef unsigned long	__kernel_ulong_t;
> > +#endif
> > +
> >  #endif /* _LINUX_POSIX_TYPES_H */
> 
> No.
> 
> The headers in uapi are automatically generated from the upstream kernel
> headers. If there are places that need to have backwards compatibility,
> fix it in the main iproute2 source.

Thanks.
But this means modifying several iproute2 source files, essentially every file
that includes (possibly indirectly) kernel.h, because that one includes
sysinfo.h which uses the __kernel_long_t type.

How do you propose to handle this? Add a new header file in include/ to hold the
two definitions with guards like above, then include that header file
unconditionally from the required files?
Something like: include/kernel_compat.h ?

Thanks,
Thomas