kernel: Add support for multiple kernel packages

Some distros may want to provide alternate kernel "flavors" via feeds or
within bootable images. For example, readily available builds which
provide certain diagnostic features can enable developers and testers to
more quickly resolve issues by avoiding lengthy kernel builds.

This change allows for building multiple flavors of the kernel and
module packages by templatizing kernel package names via a new
KERNEL_PACKAGE_NAME variable in kernel.bbclass. It defaults to the old
name of "kernel", but can be overridden by certain recipes providing
alternate kernel flavors.

To maintain compatibility, recipes providing alternate kernel flavors
cannot be the "preferred provider" for virtual/kernel. This is because
OE puts the preferred provider's build and source at
"tmp-glibc/work-shared/$MACHINE/kernel-build-artifacts/" and
"tmp-glibc/work-shared/$MACHINE/kernel-source/" instead of
"tmp-glibc/work/*/$PN/" like other recipes. Therefore, recipes using the
default KERNEL_PACKAGE_NAME="kernel" follows the old semantics -- build
in the old location and may be preferred provider -- while recipes using
all other KERNEL_PACKAGE_NAME's build from the normal WORKDIR and don't
provide "virtual/kernel".

Testing:
 1. Add `KERNEL_PACKAGE_NAME_pn-linux-yocto-tiny = "tiny-linux"`
    to local.conf so that linux-yocto-tiny may build alongside
    the main kernel (linux-yocto).
 2. `bitbake linux-yocto linux-yocto-tiny` to build both kernel flavors.
 3. Verified image and modules IPKs exist for both:
    tmp-glibc/deploy/ipk/qemux86/kernel-* for linux-yocto
    tmp-glibc/deploy/ipk/qemux86/tiny-linux* for linux-yocto-tiny
 4. Verified linux-yocto is the "preferred provider", and was built in
    shared directory: tmp-glibc/work-shared/qemux86/kernel-*
 5. Add `CORE_IMAGE_BASE_INSTALL_append_pn-core-image-base = "tiny-linux"`
    to local.conf to install both kernel flavors in core-image-base.
 6. `bitbake core-image-base` to build an image.
 7. Verified image contains two bzImage's under /boot/, with
    "yocto-standard" (linux-yocto recipe) selected to boot via symlink.

Discussion threads:
http://lists.openembedded.org/pipermail/openembedded-core/2015-December/thread.html#114122
http://lists.openembedded.org/pipermail/openembedded-core/2017-July/thread.html#139130

[YOCTO #11363]

(From OE-Core rev: 6c8c899849d101fd1b86aad0b8eed05c7c785924)

Signed-off-by: Ioan-Adrian Ratiu <adrian.ratiu@ni.com>
Signed-off-by: Gratian Crisan <gratian.crisan@ni.com>
Signed-off-by: Haris Okanovic <haris.okanovic@ni.com>
Coauthored-by: Gratian Crisan <gratian.crisan@ni.com>
Coauthored-by: Haris Okanovic <haris.okanovic@ni.com>
Coauthored-by: Josh Hernstrom <josh.hernstrom@ni.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/meta/conf/documentation.conf b/meta/conf/documentation.conf
index 081e726d4b..995b60e158 100644
--- a/meta/conf/documentation.conf
+++ b/meta/conf/documentation.conf
@@ -247,6 +247,7 @@ KERNEL_IMAGETYPE[doc] = "The type of kernel to build for a device, usually set b
 KERNEL_IMAGETYPES[doc] = "The list of types of kernel to build for a device, usually set by the machine configuration files and defaults to KERNEL_IMAGETYPE."
 KERNEL_MODULE_AUTOLOAD[doc] = "Lists kernel modules that need to be auto-loaded during boot"
 KERNEL_MODULE_PROBECONF[doc] = "Lists kernel modules for which the build system expects to find module_conf_* values that specify configuration for each of the modules"
+KERNEL_PACKAGE_NAME[doc] = "Name prefix for kernel packages. Defaults to 'kernel'."
 KERNEL_PATH[doc] = "The location of the kernel sources. This variable is set to the value of the STAGING_KERNEL_DIR within the module class (module.bbclass)."
 KERNEL_SRC[doc] = "The location of the kernel sources. This variable is set to the value of the STAGING_KERNEL_DIR within the module class (module.bbclass)."
 KFEATURE_DESCRIPTION[doc] = "Provides a short description of a configuration fragment. You use this variable in the .scc file that describes a configuration fragment file."