Re: [OE-core] [PATCH v3 03/11] kernel.bbclass: add kernel-initrd-modules meta package

Bruce Ashfield
2025-04-10T13:15:20Z

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On Thu, Apr 10, 2025 at 9:00 AM Mikko Rapeli via lists.openembedded.org
<mikko.rapeli=linaro.org@lists.openembedded.org> wrote:

> Hi,
>
> On Thu, Apr 10, 2025 at 01:42:12PM +0100, Richard Purdie wrote:
> > On Fri, 2025-04-04 at 19:29 +0300, Mikko Rapeli via
> lists.openembedded.org wrote:
> > > At the moment linux-yocto kernels for various architectures
> > > are not very modular and a lot of drivers are built into the kernel
> > > even when they are not needed at runtime. These make the main kernel
> > > binary big and slow to boot. This also impacts udev in userspace
> > > which takes a long time processing events from all these built in
> drivers,
> > > for example when udev runs in initrd.
> > >
> > > Then constructing the initrd is very device and kernel configuration
> specific.
> > > initrd image needs explicitly define which binary packages to install
> > > to avoid pulling in complex dependencies. A full set of kernel modules
> > > via kernel-modules meta package is too big for initrd and most of the
> > > drivers are not needed for use cases like "just load modules to mount
> > > main rootfs". Then the initrd configuration breaks if kernel driver
> > > is built into the kernel since the binary package doesn't exist.
> > >
> > > Introduce kernel-initrd-modules meta package to solve these problems.
> > > The meta package adds dependencies to real kernel modules based on
> > > the kernel module file paths so that it will include several
> > > kernel subsystems and their drivers which are often needed to find
> > > main rootfs from some block device. This works when drivers are built
> > > as modules but does not break if drivers are built into the kernel.
> > >
> > > The resulting initrd is also smaller since only a subset of drivers
> > > are needed for "mount the rootfs" usecase. Tested on genericarm64
> > > kernel and qemu and AMD KV260 HW.
> > >
> > > Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>
> > > ---
> > > .../kernel-module-split.bbclass | 48 +++++++++++++++++++
> > > meta/classes-recipe/kernel.bbclass | 5 +-
> > > meta/classes-recipe/module.bbclass | 37 ++++++++++++++
> > > 3 files changed, 89 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/meta/classes-recipe/kernel-module-split.bbclass
> b/meta/classes-recipe/kernel-module-split.bbclass
> > > index 9487365eb7..101c5cd959 100644
> > > --- a/meta/classes-recipe/kernel-module-split.bbclass
> > > +++ b/meta/classes-recipe/kernel-module-split.bbclass
> > > @@ -42,6 +42,40 @@ KERNEL_MODULE_PACKAGE_PREFIX ?= ""
> > > KERNEL_MODULE_PACKAGE_SUFFIX ?= "-${KERNEL_VERSION}"
> > > KERNEL_MODULE_PROVIDE_VIRTUAL ?= "1"
> > >
> > > +# subset of kernel modules needed in initrd, to e.g. mount rootfs
> from block device
> > > +KERNEL_INITRD_MODULES_META_PACKAGE ?= "${@
> d.getVar("KERNEL_PACKAGE_NAME") or "kernel" }-initrd-modules"
> > > +
> > > +# match regex to path or file name. E.g. include all drivers with
> files in path /drivers/ata/
> > > +KERNEL_INITRD_MODULES_REGEX ?= "(.*)(\
> > > +/drivers/acpi/|\
> > > +/drivers/ata/|\
> > > +/drivers/block/|\
> > > +/drivers/cdrom/|\
> > > +/drivers/char/hw_random/|\
> > > +/drivers/char/tpm/|\
> > > +/drivers/char/|\
> > > +/drivers/crypto/|\
> > > +/drivers/dax/|\
> > > +/drivers/firmware/arm_scmi/|\
> > > +/drivers/gpu/drm/|\
> > > +/drivers/md/|\
> > > +/drivers/mmc/|\
> > > +/drivers/mtd/|\
> > > +/drivers/nvdimm/|\
> > > +/drivers/nvme/|\
> > > +/drivers/pci/|\
> > > +/drivers/scsi/|\
> > > +/drivers/tee/|\
> > > +/drivers/tty/serial/|\
> > > +/drivers/virtio/|\
> > > +/drivers/watchdog/|\
> > > +/kernel/arch/|\
> > > +/kernel/block/|\
> > > +/kernel/crypto/|\
> > > +/kernel/fs/|\
> > > +/kernel/lib/\
> > > +)(.*)"
> > > +
> > > python split_kernel_module_packages () {
> > > import re
> > >
> > > @@ -183,6 +217,20 @@ python split_kernel_module_packages () {
> > > modules = do_split_packages(d,
> root='${nonarch_base_libdir}/modules', file_regex=module_regex,
> output_pattern=module_pattern, description='%s kernel module',
> postinst=postinst, postrm=postrm, recursive=True, hook=frob_metadata,
> extra_depends='%s-%s' % (kernel_package_name, kernel_version))
> > > if modules:
> > > d.appendVar('RDEPENDS:' + metapkg, ' '+' '.join(modules))
> > > +
> > > + initrd_metapkg = d.getVar('KERNEL_INITRD_MODULES_META_PACKAGE')
> or ""
> > > + initrd_module_regex = d.getVar('KERNEL_INITRD_MODULES_REGEX') or
> ""
> > > + if (initrd_metapkg != "") and (initrd_module_regex != ""):
> > > + initrd_module_regex = re.compile(initrd_module_regex)
> > > + initrd_modules = []
> > > + for module in modules:
> > > + files = d.getVar('FILES:' + module)
> > > + m = re.match(initrd_module_regex, files)
> > > + if m:
> > > + initrd_modules.append(module)
> > > +
> > > + if initrd_modules:
> > > + d.appendVar('RDEPENDS:' + initrd_metapkg, ' '+'
> '.join(initrd_modules))
> > > }
> > >
> > > do_package[vardeps] += '${@" ".join(map(lambda s: "module_conf_" + s,
> (d.getVar("KERNEL_MODULE_PROBECONF") or "").split()))}'
> > > diff --git a/meta/classes-recipe/kernel.bbclass
> b/meta/classes-recipe/kernel.bbclass
> > > index 36ce659762..3dcaebcaed 100644
> > > --- a/meta/classes-recipe/kernel.bbclass
> > > +++ b/meta/classes-recipe/kernel.bbclass
> > > @@ -695,13 +695,14 @@ EXPORT_FUNCTIONS do_compile do_transform_kernel
> do_transform_bundled_initramfs d
> > >
> > > # kernel-base becomes kernel-${KERNEL_VERSION}
> > > # kernel-image becomes kernel-image-${KERNEL_VERSION}
> > > -PACKAGES = "${KERNEL_PACKAGE_NAME} ${KERNEL_PACKAGE_NAME}-base
> ${KERNEL_PACKAGE_NAME}-vmlinux ${KERNEL_PACKAGE_NAME}-image
> ${KERNEL_PACKAGE_NAME}-dev ${KERNEL_PACKAGE_NAME}-modules
> ${KERNEL_PACKAGE_NAME}-dbg"
> > > +PACKAGES = "${KERNEL_PACKAGE_NAME} ${KERNEL_PACKAGE_NAME}-base
> ${KERNEL_PACKAGE_NAME}-vmlinux ${KERNEL_PACKAGE_NAME}-image
> ${KERNEL_PACKAGE_NAME}-dev ${KERNEL_PACKAGE_NAME}-modules
> ${KERNEL_PACKAGE_NAME}-initrd-modules ${KERNEL_PACKAGE_NAME}-dbg"
> > > FILES:${PN} = ""
> > > FILES:${KERNEL_PACKAGE_NAME}-base =
> "${nonarch_base_libdir}/modules/${KERNEL_VERSION}/modules.order
> ${nonarch_base_libdir}/modules/${KERNEL_VERSION}/modules.builtin
> ${nonarch_base_libdir}/modules/${KERNEL_VERSION}/modules.builtin.modinfo"
> > > FILES:${KERNEL_PACKAGE_NAME}-image = ""
> > > FILES:${KERNEL_PACKAGE_NAME}-dev = "/${KERNEL_IMAGEDEST}/System.map*
> /${KERNEL_IMAGEDEST}/Module.symvers* /${KERNEL_IMAGEDEST}/config*
> ${KERNEL_SRC_PATH} ${nonarch_base_libdir}/modules/${KERNEL_VERSION}/build"
> > > FILES:${KERNEL_PACKAGE_NAME}-vmlinux =
> "/${KERNEL_IMAGEDEST}/vmlinux-${KERNEL_VERSION_NAME}"
> > > FILES:${KERNEL_PACKAGE_NAME}-modules = ""
> > > +FILES:${KERNEL_PACKAGE_NAME}-initrd-modules = ""
> > > FILES:${KERNEL_PACKAGE_NAME}-dbg = "/usr/lib/debug /usr/src/debug"
> > > RDEPENDS:${KERNEL_PACKAGE_NAME} = "${KERNEL_PACKAGE_NAME}-base (=
> ${EXTENDPKGV})"
> > > # Allow machines to override this dependency if kernel image files are
> > > @@ -716,7 +717,9 @@ ALLOW_EMPTY:${KERNEL_PACKAGE_NAME} = "1"
> > > ALLOW_EMPTY:${KERNEL_PACKAGE_NAME}-base = "1"
> > > ALLOW_EMPTY:${KERNEL_PACKAGE_NAME}-image = "1"
> > > ALLOW_EMPTY:${KERNEL_PACKAGE_NAME}-modules = "1"
> > > +ALLOW_EMPTY:${KERNEL_PACKAGE_NAME}-initrd-modules = "1"
> > > DESCRIPTION:${KERNEL_PACKAGE_NAME}-modules = "Kernel modules meta
> package"
> > > +DESCRIPTION:${KERNEL_PACKAGE_NAME}-initrd-modules = "Kernel initrd
> modules meta package"
> > >
> > > pkg_postinst:${KERNEL_PACKAGE_NAME}-base () {
> > > if [ ! -e "$D/lib/modules/${KERNEL_VERSION}" ]; then
> > > diff --git a/meta/classes-recipe/module.bbclass
> b/meta/classes-recipe/module.bbclass
> > > index f2f0b25a2d..51f864f1f9 100644
> > > --- a/meta/classes-recipe/module.bbclass
> > > +++ b/meta/classes-recipe/module.bbclass
> > > @@ -86,3 +86,40 @@ EXPORT_FUNCTIONS do_compile do_install
> > > KERNEL_MODULES_META_PACKAGE = "${PN}"
> > > FILES:${PN} = ""
> > > ALLOW_EMPTY:${PN} = "1"
> > > +
> > > +# subset of kernel modules needed in initrd, to e.g. mount rootfs
> from block device
> > > +KERNEL_INITRD_MODULES_META_PACKAGE ?= "${@
> d.getVar("KERNEL_PACKAGE_NAME") or "kernel" }-initrd-modules"
> > > +
> > > +# match regex to path or file name. E.g. include all drivers with
> files in path /drivers/ata/
> > > +KERNEL_INITRD_MODULES_REGEX ?= "(.*)(\
> > > +/drivers/acpi/|\
> > > +/drivers/ata/|\
> > > +/drivers/block/|\
> > > +/drivers/cdrom/|\
> > > +/drivers/char/hw_random/|\
> > > +/drivers/char/tpm/|\
> > > +/drivers/char/|\
> > > +/drivers/crypto/|\
> > > +/drivers/dax/|\
> > > +/drivers/firmware/arm_scmi/|\
> > > +/drivers/gpu/drm/|\
> > > +/drivers/md/|\
> > > +/drivers/mmc/|\
> > > +/drivers/mtd/|\
> > > +/drivers/nvdimm/|\
> > > +/drivers/nvme/|\
> > > +/drivers/pci/|\
> > > +/drivers/scsi/|\
> > > +/drivers/tee/|\
> > > +/drivers/tty/serial/|\
> > > +/drivers/virtio/|\
> > > +/drivers/watchdog/|\
> > > +/kernel/arch/|\
> > > +/kernel/block/|\
> > > +/kernel/crypto/|\
> > > +/kernel/fs/|\
> > > +/kernel/lib/\
> > > +)(.*)"
> > > +
> > > +FILES:${PN}-initrd = ""
> > > +ALLOW_EMPTY:${PN}-initrd = "1"
> >
> > What is the difference between the variable defined in kernel-module-
> > split.bbclass and this one in module.bbclass? Do we need/want to
> > separate but seemingly similar definitions?
>
> One is for kernel compilation and in-tree drivers, the other is for
> out-of-tree modules.
>
> The "kernel-modules" meta package is handled this way too, with
> duplication in both.
>
> Bruce says this should be moved to linux-yocto kernel recipe,
> which IMO breaks the use of kernel-initrd-modules for vendor kernel recipes
> outside of oe-core. I'd rather support them too to e.g. more easily boot
> qemu or run oeqa selftests with qemu.
>

That's not quite what I said (but it is close), I said it shouldn't be
defined
at the base with no requirement opt-in from a recipe (even if this way
of constructing an initrd with the modules is not the default). It is a (
weak)
binding to specific kernel versions and directory layouts, but it is a
binding
none the less. If it sits at the base in the classes no one will ever look
at
it or even know that it should be considered.

My suggestion was not that it should only be in linux-yocto (but I'd
insist on overriding it or doing it slightly differently in linux-yocto),
I was saying that it I think that the two definitions are far to similar
and even if there remain two definitions, they should be moved
into a .inc file.

Any kernel recipe that wants to build an initrd like this can opt-in by
including the .inc, and/or creating their own definition.

Bruce

>
> Cheers,
>
> -Mikko
>
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