Re: [dpdk-dev] [RFC PATCH v4] build: kni cross-compilation support

["Juraj Linkeš" <juraj.linkes@pantheon.tech>]

> -----Original Message-----
> From: Bruce Richardson <bruce.richardson@intel.com>
> Sent: Friday, February 5, 2021 4:27 PM
> To: Juraj Linkeš <juraj.linkes@pantheon.tech>
> Cc: thomas@monjalon.net; Ruifeng.Wang@arm.com;
> Honnappa.Nagarahalli@arm.com; jerinjacobk@gmail.com;
> hemant.agrawal@nxp.com; ferruh.yigit@intel.com; aboyer@pensando.io;
> dev@dpdk.org; david.marchand@redhat.com; bluca@debian.org
> Subject: Re: [RFC PATCH v4] build: kni cross-compilation support
> 
> On Fri, Feb 05, 2021 at 04:04:32PM +0100, Juraj Linkeš wrote:
> > The kni linux module is using a custom target for building, which
> > doesn't take into account any cross compilation arguments. The
> > arguments in question are ARCH, CROSS_COMPILE (for gcc, clang) and CC,
> > LD (for clang). Get those from the cross file and pass them to the
> > custom target.
> >
> > The user supplied path may not contain the 'build' directory, such as
> > when using cross-compiled headers, so only append that in the default
> > case (when no path is supplied in native builds) and use the
> > unmodified path from the user otherwise. Also modify the install path
> accordingly.
> >
> > Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>
> > ---
> 
> Thanks, this all looks ok to me now, bar one very minor nit below. Doing a native
> build on my system with the running kernel also works fine.
> 
> However, the bigger question is one of compatibility for this change. The current
> documentation for the kernel_dir option is:
>   option('kernel_dir', type: 'string', value: '',
> 	description: 'Path to the kernel for building kernel modules. \
> 	Headers must be in $kernel_dir/build. Modules will be installed \
> 	in $DEST_DIR/$kernel_dir/extra/dpdk.')
> 
> Obviously the description now needs an update to reflect the new use

I'll change the description. The current patch version is always installing the modules into '/lib/modules/' + kernel_version + '/extra/dpdk', though. I don't think we want to change the behavior this way, so I'll make the changes to preserve to original behavior ('/lib/modules/' + kernel_version + '/extra/dpdk' when kernel_dir is not supplied, kernel_dir + '/extra/dpdk' when it is).

> , but I'm
> not sure if changing the behaviour counts as an "ABI" change or not, and
> whether it needs to wait for a new LTS release. Any scripts that were compiling
> using e.g. kernel_dir='/lib/modules/<version>' need to be changed to use
> kernel_dir='/lib/modules/<version>/build' instead.
> 

I'm not sure what to do with this. Should I make it backwards compatible by checking the build dir as well (i.e. trying make kernelversion in both $kernel_dir and $kernel_dir/build)?

> /Bruce
> 
> >  kernel/linux/kni/meson.build |  8 ++--
> >  kernel/linux/meson.build     | 80 ++++++++++++++++++++++++++++++------
> >  2 files changed, 71 insertions(+), 17 deletions(-)
> >
> > diff --git a/kernel/linux/kni/meson.build
> > b/kernel/linux/kni/meson.build index 07e0c9dae7..46b71c7418 100644
> > --- a/kernel/linux/kni/meson.build
> > +++ b/kernel/linux/kni/meson.build
> > @@ -13,7 +13,7 @@ kni_sources = files(  custom_target('rte_kni',
> >  	input: kni_sources,
> >  	output: 'rte_kni.ko',
> > -	command: ['make', '-j4', '-C', kernel_dir + '/build',
> > +	command: ['make', '-j4', '-C', kernel_build_dir,
> >  		'M=' + meson.current_build_dir(),
> >  		'src=' + meson.current_source_dir(),
> >  		'MODULE_CFLAGS=-include ' + meson.source_root() +
> > '/config/rte_config.h' + @@ -21,8 +21,8 @@ custom_target('rte_kni',
> >  		' -I' + meson.source_root() + '/lib/librte_kni' +
> >  		' -I' + meson.build_root() +
> >  		' -I' + meson.current_source_dir(),
> > -		'modules'],
> > +		'modules'] + cross_args,
> >  	depends: kni_mkfile,
> > -	install: true,
> > -	install_dir: kernel_dir + '/extra/dpdk',
> > +	install: install,
> > +	install_dir: kernel_install_dir,
> >  	build_by_default: get_option('enable_kmods')) diff --git
> > a/kernel/linux/meson.build b/kernel/linux/meson.build index
> > 5c864a4653..7acb52944f 100644
> > --- a/kernel/linux/meson.build
> > +++ b/kernel/linux/meson.build
> > @@ -3,25 +3,79 @@
> >
> >  subdirs = ['kni']
> >
> > -# if we are cross-compiling we need kernel_dir specified -if
> > get_option('kernel_dir') == '' and meson.is_cross_build()
> > -	error('Need "kernel_dir" option for kmod compilation when cross-
> compiling')
> > -endif
> > +kernel_build_dir = get_option('kernel_dir') install = not
> > +meson.is_cross_build() cross_args = [] kernel_install_dir = ''
> 
> Minor nit, I'd have kernel_install_dir immediately after kernel_build_dir in the list
> above.
> 

Sure.