svn commit: r339901 - head/sys/conf

[Ian Lepore]

On Tue, 2018-10-30 at 09:40 -0700, John Baldwin wrote:
> On 10/29/18 5:23 PM, John Baldwin wrote:
> > 
> > Author: jhb
> > Date: Tue Oct 30 00:23:37 2018
> > New Revision: 339901
> > URL: https://svnweb.freebsd.org/changeset/base/339901
> > 
> > Log:
> >   Permit local kernel modules to be built as part of a kernel build.
> >   
> >   Add support for "local" modules.  By default, these modules are
> >   located in LOCALBASE/sys/modules (where LOCALBASE defaults to
> >   /usr/local).  Individual modules can be built along with a kernel by
> >   defining LOCAL_MODULES to the list of modules.  Each is assumed to be
> >   a subdirectory containing a valid Makefile.  If LOCAL_MODULES is not
> >   specified, all of the modules present in LOCALBASE/sys/modules are
> >   built and installed along with the kernel.
> >   
> >   This means that a port that installs a kernel module can choose to
> >   install its source along with a suitable Makefile to
> >   /usr/local/sys/modules/.  Future kernel builds will then include
> >   that kernel module using the kernel configuration's opt_*.h headers
> >   and install it into /boot/kernel along with other kernel-specific
> >   modules.
> >   
> >   This is not trying to solve the issue of folks running GENERIC release
> >   kernels, but is instead aimed at folks who build their own kernels.
> >   For those folks this ensures that kernel modules from ports will
> >   always be using the right KBI, etc.  This includes folks running any
> >   KBI-breaking kernel configs (such as PAE).
> >   
> >   There are still some kinks to be worked out with cross-building (we
> >   probably shouldn't include local modules in cross-built kernels by
> >   default), but this is a sufficient starting point.
> The intention is that if, say, the drm-kmod ports install a valid module
> Makefile to /usr/local/sys/modules/drm/Makefile, then subsequent kernel
> builds will automatically pull in that module.  Also, since "local"
> modules are built after in-tree modules, if a ports module has the same
> filename (foo.ko), it will be installed over top of the in-tree one
> in /boot/kernel effectively replacing it.  Note that as with subdirectories
> in sys/modules, a Makefile could just be a bsd.subdir.mk that installs
> multiple modules.
> 
> I do think that as a further step we might consider having certain ports
> stop installing binary kernel modules altogether and only ship source
> (especially ports with strong KBI ties to the kernel such as virtualbox
> or drm).  Probably these ports would then use a post-install step to
> compile against whatever source tree is present on the host and install
> the module to /boot/modules.  Anyone compiling custom kernels wouldn't
> use that module though after the next kernel recompile as the next kernel
> would include a kernel-specific version in /boot/kernel that would take
> precedence over the version in /boot/modules.  However, that version in
> /boot/modules would still be needed for folks running release kernels that
> never compile a kernel.  Further thought is probably required for the
> "stock kernel" case to make sure we are really happy with that approach.
> 
> Cross-building kernels is also a further consideration.  The current
> patch always opts-in to building local modules unless you explicitly
> out out by setting LOCAL_MODULES to an empty string or LOCALBASE to
> something that doesn't exist.  This means that if you have a port/package
> installed that ships kernel module sources and do a 'make tinderbox',
> we will try to build that module on all architectures that build modules.
> This is probably not what we want.  I did want this feature to default
> to enabled for native kernels so that installing a port will Just Work(tm)
> without requiring kernel config changes to enable modules and I'd like
> to keep that.  Some thoughts I'm considering for cross-builds are:
> 
> 1) Change the buildkernel and installkernel targets in Makefile.inc1
>    to explicitly pass LOCALBASE=/nonexistent as a parameter to make
>    if TARGET_ARCH != MACHINE_ARCH or TARGET != MACHINE.  A user could
>    explicitly request local modules for a kernel build by setting
>    LOCALBASE explicitly when invoking buildkernel/installkernel.
> 

Or something like

.if ${TARGET_ARCH} != ${MACHINE_ARCH}
LOCALBASE?= /usr/local/${TARGET_ARCH}
.endif

Then it's analogous under /usr/local to the /usr/src/${TARGET_ARCH}
hierarchy that's used for cross-building base. This is how Warner set
up the ports crossbuild mechanisms years ago that we still use at
$work.

-- Ian