Re: [PATCH] linux-module: make sure out-of-tree modules win over built-in

[Henning Schild <henning.schild@siemens.com>]

Am Fri, 26 Aug 2022 13:34:22 +0200
schrieb "Bezdeka, Florian (T CED SES-DE)" <florian.bezdeka@siemens.com>:

> On Thu, 2022-08-25 at 22:40 +0200, Henning Schild wrote:
> > If we built an out of tree module that happens to be already part
> > of the kernel, 
> >   
> 
> This hopefully does not happen in the wild and is likely a very
> special situation we're facing internally while working on
> upstreaming some driver stuff.

That period is going to be very long, like years. And it is rare but
valid. Any board could require a slightly modified version of a driver
already in the kernel, and if it is just a backport of something new
not yet in your old kernel.

While the conflict could also be solved with recompiling that kernel,
with the conflicting driver disabled, that would be kind of a big deal
to solve such a small issue.

> I'm not sure if this is really relevant for Isar itself. If the
> decision is "let's take it", I would vote for "disabled per default".

I think it is relevant, that is why i propose it.

But yes, we could maybe not say "INSTALL_MOD_DIR ?= "extra"" but maybe
allow for an array of "EXTRA_FILES". That would also allow to ship
things like /etc/modprobe.d/ and /etc/udev.d/.

Or we could make the pattern that such EXTRA_FILES would have to come
from another BSP package which the module package itself would depend
on. All there would be to do is to write that extra package and allow
the modification of "Depends:" of an Isar built module package.

I think i might give that last approach a try, all Isar would need to
do is allow that Depends to change. Might feel a little obfuscated in
the end, especially if others might want to do similar things. But let
us see.

Henning

> > we want to make sure depmod prefers the external one. In order
> > to do so simply include a config file into every module package, by
> > default using the kernels default INSTALL_MOD_DIR which is "extra".
> > 
> > Should there be multiple modules using different such directories,
> > all recipes should set INSTALL_MOD_DIR listing them all in the
> > desired order. That interface for multiple such very special
> > modules is not nice but since they are pretty special it might be
> > just good enough.
> > 
> > Reported-by: Pingfang Liao <Pingfang.Liao@siemens.com>
> > Signed-off-by: Henning Schild <henning.schild@siemens.com>
> > ---
> >  meta/recipes-kernel/linux-module/files/debian/rules.tmpl | 1 +
> >  meta/recipes-kernel/linux-module/module.inc              | 3 +++
> >  2 files changed, 4 insertions(+)
> > 
> > diff --git
> > a/meta/recipes-kernel/linux-module/files/debian/rules.tmpl
> > b/meta/recipes-kernel/linux-module/files/debian/rules.tmpl index
> > d3bd7dc30f21..abd3c88fac7e 100755 ---
> > a/meta/recipes-kernel/linux-module/files/debian/rules.tmpl +++
> > b/meta/recipes-kernel/linux-module/files/debian/rules.tmpl @@ -55,6
> > +55,7 @@ override_dh_auto_build: override_dh_auto_install:
> >  	$(MAKE) -C $(KDIR) M=$(PWD)
> > INSTALL_MOD_PATH=$(PWD)/debian/${PN} modules_install
> > +	install -D -m 0644 $(PWD)/debian/${PN}.conf
> > $(PWD)/debian/${PN}/usr/lib/depmod.d/${PN}.conf 
> >  %:
> >  	CFLAGS= LDFLAGS= dh $@ --parallel
> > diff --git a/meta/recipes-kernel/linux-module/module.inc
> > b/meta/recipes-kernel/linux-module/module.inc index
> > b20ec32ae20a..475e7aef05ea 100644 ---
> > a/meta/recipes-kernel/linux-module/module.inc +++
> > b/meta/recipes-kernel/linux-module/module.inc @@ -29,9 +29,12 @@
> > TEMPLATE_FILES = "debian/control.tmpl \ debian/rules.tmpl"
> >  TEMPLATE_VARS += "KERNEL_NAME KERNEL_TYPE KERNEL_IMAGE_PKG
> > KERNEL_HEADERS_PKG DEBIAN_BUILD_DEPENDS PN" 
> > +INSTALL_MOD_DIR ?= "extra"
> > +
> >  do_prepare_build() {
> >      cp -r ${WORKDIR}/debian ${S}/
> >  
> > +    echo "search ${INSTALL_MOD_DIR} built-in" >
> > ${S}/debian/${PN}.conf for module in ${AUTOLOAD}; do
> >          echo "echo $module >> /etc/modules" >> ${S}/debian/postinst
> >      done
> > -- 
> > 2.35.1
> >   
>