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diff --git a/documentation/kernel-dev/kernel-dev-advanced.xml b/documentation/kernel-dev/kernel-dev-advanced.xml deleted file mode 100644 index 37177966bf..0000000000 --- a/documentation/kernel-dev/kernel-dev-advanced.xml +++ /dev/null @@ -1,1257 +0,0 @@ -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" -"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" -[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] > -<!--SPDX-License-Identifier: CC-BY-2.0-UK--> - -<chapter id='kernel-dev-advanced'> -<title>Working with Advanced Metadata (<filename>yocto-kernel-cache</filename>)</title> - -<section id='kernel-dev-advanced-overview'> - <title>Overview</title> - - <para> - In addition to supporting configuration fragments and patches, the - Yocto Project kernel tools also support rich - <ulink url='&YOCTO_DOCS_REF_URL;#metadata'>Metadata</ulink> that you can - use to define complex policies and Board Support Package (BSP) support. - The purpose of the Metadata and the tools that manage it is - to help you manage the complexity of the configuration and sources - used to support multiple BSPs and Linux kernel types. - </para> - - <para> - Kernel Metadata exists in many places. - One area in the Yocto Project - <ulink url='&YOCTO_DOCS_OM_URL;#source-repositories'>Source Repositories</ulink> - is the <filename>yocto-kernel-cache</filename> Git repository. - You can find this repository grouped under the "Yocto Linux Kernel" - heading in the - <ulink url='&YOCTO_GIT_URL;'>Yocto Project Source Repositories</ulink>. - </para> - - <para> - Kernel development tools ("kern-tools") exist also in the Yocto - Project Source Repositories under the "Yocto Linux Kernel" heading - in the <filename>yocto-kernel-tools</filename> Git repository. - The recipe that builds these tools is - <filename>meta/recipes-kernel/kern-tools/kern-tools-native_git.bb</filename> - in the - <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink> - (e.g. <filename>poky</filename>). - </para> -</section> - -<section id='using-kernel-metadata-in-a-recipe'> - <title>Using Kernel Metadata in a Recipe</title> - - <para> - As mentioned in the introduction, the Yocto Project contains kernel - Metadata, which is located in the - <filename>yocto-kernel-cache</filename> Git repository. - This Metadata defines Board Support Packages (BSPs) that - correspond to definitions in linux-yocto recipes for corresponding BSPs. - A BSP consists of an aggregation of kernel policy and enabled - hardware-specific features. - The BSP can be influenced from within the linux-yocto recipe. - <note> - A Linux kernel recipe that contains kernel Metadata (e.g. - inherits from the <filename>linux-yocto.inc</filename> file) - is said to be a "linux-yocto style" recipe. - </note> - </para> - - <para> - Every linux-yocto style recipe must define the - <ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink> - variable. - This variable is typically set to the same value as the - <filename>MACHINE</filename> variable, which is used by - <ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink>. - However, in some cases, the variable might instead refer to the - underlying platform of the <filename>MACHINE</filename>. - </para> - - <para> - Multiple BSPs can reuse the same <filename>KMACHINE</filename> - name if they are built using the same BSP description. - Multiple Corei7-based BSPs could share the same "intel-corei7-64" - value for <filename>KMACHINE</filename>. - It is important to realize that <filename>KMACHINE</filename> is - just for kernel mapping, while <filename>MACHINE</filename> - is the machine type within a BSP Layer. - Even with this distinction, however, these two variables can hold - the same value. - See the <link linkend='bsp-descriptions'>BSP Descriptions</link> - section for more information. - </para> - - <para> - Every linux-yocto style recipe must also indicate the Linux kernel - source repository branch used to build the Linux kernel. - The <ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink> - variable must be set to indicate the branch. - <note> - You can use the <filename>KBRANCH</filename> value to define an - alternate branch typically with a machine override as shown here - from the <filename>meta-yocto-bsp</filename> layer: - <literallayout class='monospaced'> - KBRANCH_edgerouter = "standard/edgerouter" - </literallayout> - </note> - </para> - - <para> - The linux-yocto style recipes can optionally define the following - variables: - <literallayout class='monospaced'> - KERNEL_FEATURES - LINUX_KERNEL_TYPE - </literallayout> - </para> - - <para> - <ulink url='&YOCTO_DOCS_REF_URL;#var-LINUX_KERNEL_TYPE'><filename>LINUX_KERNEL_TYPE</filename></ulink> - defines the kernel type to be - used in assembling the configuration. - If you do not specify a <filename>LINUX_KERNEL_TYPE</filename>, - it defaults to "standard". - Together with <filename>KMACHINE</filename>, - <filename>LINUX_KERNEL_TYPE</filename> defines the search - arguments used by the kernel tools to find the - appropriate description within the kernel Metadata with which to - build out the sources and configuration. - The linux-yocto recipes define "standard", "tiny", and "preempt-rt" - kernel types. - See the "<link linkend='kernel-types'>Kernel Types</link>" section - for more information on kernel types. - </para> - - <para> - During the build, the kern-tools search for the BSP description - file that most closely matches the <filename>KMACHINE</filename> - and <filename>LINUX_KERNEL_TYPE</filename> variables passed in from the - recipe. - The tools use the first BSP description it finds that match - both variables. - If the tools cannot find a match, they issue a warning. - </para> - - <para> - The tools first search for the <filename>KMACHINE</filename> and - then for the <filename>LINUX_KERNEL_TYPE</filename>. - If the tools cannot find a partial match, they will use the - sources from the <filename>KBRANCH</filename> and any configuration - specified in the - <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>. - </para> - - <para> - You can use the - <ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'><filename>KERNEL_FEATURES</filename></ulink> - variable - to include features (configuration fragments, patches, or both) that - are not already included by the <filename>KMACHINE</filename> and - <filename>LINUX_KERNEL_TYPE</filename> variable combination. - For example, to include a feature specified as - "features/netfilter/netfilter.scc", - specify: - <literallayout class='monospaced'> - KERNEL_FEATURES += "features/netfilter/netfilter.scc" - </literallayout> - To include a feature called "cfg/sound.scc" just for the - <filename>qemux86</filename> machine, specify: - <literallayout class='monospaced'> - KERNEL_FEATURES_append_qemux86 = " cfg/sound.scc" - </literallayout> - The value of the entries in <filename>KERNEL_FEATURES</filename> - are dependent on their location within the kernel Metadata itself. - The examples here are taken from the - <filename>yocto-kernel-cache</filename> repository. - Each branch of this repository contains "features" and "cfg" - subdirectories at the top-level. - For more information, see the - "<link linkend='kernel-metadata-syntax'>Kernel Metadata Syntax</link>" - section. - </para> -</section> - -<section id='kernel-metadata-syntax'> - <title>Kernel Metadata Syntax</title> - - <para> - The kernel Metadata consists of three primary types of files: - <filename>scc</filename> - <footnote> - <para> - <filename>scc</filename> stands for Series Configuration - Control, but the naming has less significance in the - current implementation of the tooling than it had in the - past. - Consider <filename>scc</filename> files to be description files. - </para> - </footnote> - description files, configuration fragments, and patches. - The <filename>scc</filename> files define variables and include or - otherwise reference any of the three file types. - The description files are used to aggregate all types of kernel - Metadata into - what ultimately describes the sources and the configuration required - to build a Linux kernel tailored to a specific machine. - </para> - - <para> - The <filename>scc</filename> description files are used to define two - fundamental types of kernel Metadata: - <itemizedlist> - <listitem><para>Features</para></listitem> - <listitem><para>Board Support Packages (BSPs)</para></listitem> - </itemizedlist> - </para> - - <para> - Features aggregate sources in the form of patches and configuration - fragments into a modular reusable unit. - You can use features to implement conceptually separate kernel - Metadata descriptions such as pure configuration fragments, - simple patches, complex features, and kernel types. - <link linkend='kernel-types'>Kernel types</link> define general - kernel features and policy to be reused in the BSPs. - </para> - - <para> - BSPs define hardware-specific features and aggregate them with kernel - types to form the final description of what will be assembled and built. - </para> - - <para> - While the kernel Metadata syntax does not enforce any logical - separation of configuration fragments, patches, features or kernel - types, best practices dictate a logical separation of these types - of Metadata. - The following Metadata file hierarchy is recommended: - <literallayout class='monospaced'> - <replaceable>base</replaceable>/ - bsp/ - cfg/ - features/ - ktypes/ - patches/ - </literallayout> - </para> - - <para> - The <filename>bsp</filename> directory contains the - <link linkend='bsp-descriptions'>BSP descriptions</link>. - The remaining directories all contain "features". - Separating <filename>bsp</filename> from the rest of the structure - aids conceptualizing intended usage. - </para> - - <para> - Use these guidelines to help place your <filename>scc</filename> - description files within the structure: - <itemizedlist> - <listitem><para>If your file contains - only configuration fragments, place the file in the - <filename>cfg</filename> directory.</para></listitem> - <listitem><para>If your file contains - only source-code fixes, place the file in the - <filename>patches</filename> directory.</para></listitem> - <listitem><para>If your file encapsulates - a major feature, often combining sources and configurations, - place the file in <filename>features</filename> directory. - </para></listitem> - <listitem><para>If your file aggregates - non-hardware configuration and patches in order to define a - base kernel policy or major kernel type to be reused across - multiple BSPs, place the file in <filename>ktypes</filename> - directory. - </para></listitem> - </itemizedlist> - </para> - - <para> - These distinctions can easily become blurred - especially as - out-of-tree features slowly merge upstream over time. - Also, remember that how the description files are placed is - a purely logical organization and has no impact on the functionality - of the kernel Metadata. - There is no impact because all of <filename>cfg</filename>, - <filename>features</filename>, <filename>patches</filename>, and - <filename>ktypes</filename>, contain "features" as far as the kernel - tools are concerned. - </para> - - <para> - Paths used in kernel Metadata files are relative to - <replaceable>base</replaceable>, which is either - <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink> - if you are creating Metadata in - <link linkend='recipe-space-metadata'>recipe-space</link>, - or the top level of - <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/yocto-kernel-cache/tree/'><filename>yocto-kernel-cache</filename></ulink> - if you are creating - <link linkend='metadata-outside-the-recipe-space'>Metadata outside of the recipe-space</link>. - </para> - - <section id='configuration'> - <title>Configuration</title> - - <para> - The simplest unit of kernel Metadata is the configuration-only - feature. - This feature consists of one or more Linux kernel configuration - parameters in a configuration fragment file - (<filename>.cfg</filename>) and a <filename>.scc</filename> file - that describes the fragment. - </para> - - <para> - As an example, consider the Symmetric Multi-Processing (SMP) - fragment used with the <filename>linux-yocto-4.12</filename> - kernel as defined outside of the recipe space (i.e. - <filename>yocto-kernel-cache</filename>). - This Metadata consists of two files: <filename>smp.scc</filename> - and <filename>smp.cfg</filename>. - You can find these files in the <filename>cfg</filename> directory - of the <filename>yocto-4.12</filename> branch in the - <filename>yocto-kernel-cache</filename> Git repository: - <literallayout class='monospaced'> - cfg/smp.scc: - define KFEATURE_DESCRIPTION "Enable SMP for 32 bit builds" - define KFEATURE_COMPATIBILITY all - - kconf hardware smp.cfg - - cfg/smp.cfg: - CONFIG_SMP=y - CONFIG_SCHED_SMT=y - # Increase default NR_CPUS from 8 to 64 so that platform with - # more than 8 processors can be all activated at boot time - CONFIG_NR_CPUS=64 - # The following is needed when setting NR_CPUS to something - # greater than 8 on x86 architectures, it should be automatically - # disregarded by Kconfig when using a different arch - CONFIG_X86_BIGSMP=y - </literallayout> - You can find general information on configuration fragment files in - the - "<link linkend='creating-config-fragments'>Creating Configuration Fragments</link>" - section. - </para> - - <para> - Within the <filename>smp.scc</filename> file, the - <ulink url='&YOCTO_DOCS_REF_URL;#var-KFEATURE_DESCRIPTION'><filename>KFEATURE_DESCRIPTION</filename></ulink> - statement provides a short description of the fragment. - Higher level kernel tools use this description. - </para> - - <para> - Also within the <filename>smp.scc</filename> file, the - <filename>kconf</filename> command includes the - actual configuration fragment in an <filename>.scc</filename> - file, and the "hardware" keyword identifies the fragment as - being hardware enabling, as opposed to general policy, - which would use the "non-hardware" keyword. - The distinction is made for the benefit of the configuration - validation tools, which warn you if a hardware fragment - overrides a policy set by a non-hardware fragment. - <note> - The description file can include multiple - <filename>kconf</filename> statements, one per fragment. - </note> - </para> - - <para> - As described in the - "<link linkend='validating-configuration'>Validating Configuration</link>" - section, you can use the following BitBake command to audit your - configuration: - <literallayout class='monospaced'> - $ bitbake linux-yocto -c kernel_configcheck -f - </literallayout> - </para> - </section> - - <section id='patches'> - <title>Patches</title> - - <para> - Patch descriptions are very similar to configuration fragment - descriptions, which are described in the previous section. - However, instead of a <filename>.cfg</filename> file, these - descriptions work with source patches (i.e. - <filename>.patch</filename> files). - </para> - - <para> - A typical patch includes a description file and the patch itself. - As an example, consider the build patches used with the - <filename>linux-yocto-4.12</filename> kernel as defined outside of - the recipe space (i.e. <filename>yocto-kernel-cache</filename>). - This Metadata consists of several files: - <filename>build.scc</filename> and a set of - <filename>*.patch</filename> files. - You can find these files in the <filename>patches/build</filename> - directory of the <filename>yocto-4.12</filename> branch in the - <filename>yocto-kernel-cache</filename> Git repository. - </para> - - <para> - The following listings show the <filename>build.scc</filename> - file and part of the - <filename>modpost-mask-trivial-warnings.patch</filename> file: - <literallayout class='monospaced'> - patches/build/build.scc: - patch arm-serialize-build-targets.patch - patch powerpc-serialize-image-targets.patch - patch kbuild-exclude-meta-directory-from-distclean-processi.patch - - # applied by kgit - # patch kbuild-add-meta-files-to-the-ignore-li.patch - - patch modpost-mask-trivial-warnings.patch - patch menuconfig-check-lxdiaglog.sh-Allow-specification-of.patch - - patches/build/modpost-mask-trivial-warnings.patch: - From bd48931bc142bdd104668f3a062a1f22600aae61 Mon Sep 17 00:00:00 2001 - From: Paul Gortmaker <paul.gortmaker@windriver.com> - Date: Sun, 25 Jan 2009 17:58:09 -0500 - Subject: [PATCH] modpost: mask trivial warnings - - Newer HOSTCC will complain about various stdio fcns because - . - . - . - char *dump_write = NULL, *files_source = NULL; - int opt; - -- - 2.10.1 - - generated by cgit v0.10.2 at 2017-09-28 15:23:23 (GMT) - </literallayout> - The description file can include multiple patch statements where - each statement handles a single patch. - In the example <filename>build.scc</filename> file, five patch - statements exist for the five patches in the directory. - </para> - - <para> - You can create a typical <filename>.patch</filename> file using - <filename>diff -Nurp</filename> or - <filename>git format-patch</filename> commands. - For information on how to create patches, see the - "<link linkend='using-devtool-to-patch-the-kernel'>Using <filename>devtool</filename> to Patch the Kernel</link>" - and - "<link linkend='using-traditional-kernel-development-to-patch-the-kernel'>Using Traditional Kernel Development to Patch the Kernel</link>" - sections. - </para> - </section> - - <section id='features'> - <title>Features</title> - - <para> - Features are complex kernel Metadata types that consist - of configuration fragments, patches, and possibly other feature - description files. - As an example, consider the following generic listing: - <literallayout class='monospaced'> - features/<replaceable>myfeature</replaceable>.scc - define KFEATURE_DESCRIPTION "Enable <replaceable>myfeature</replaceable>" - - patch 0001-<replaceable>myfeature</replaceable>-core.patch - patch 0002-<replaceable>myfeature</replaceable>-interface.patch - - include cfg/<replaceable>myfeature</replaceable>_dependency.scc - kconf non-hardware <replaceable>myfeature</replaceable>.cfg - </literallayout> - This example shows how the <filename>patch</filename> and - <filename>kconf</filename> commands are used as well as - how an additional feature description file is included with - the <filename>include</filename> command. - </para> - - <para> - Typically, features are less granular than configuration - fragments and are more likely than configuration fragments - and patches to be the types of things you want to specify - in the <filename>KERNEL_FEATURES</filename> variable of the - Linux kernel recipe. - See the "<link linkend='using-kernel-metadata-in-a-recipe'>Using Kernel Metadata in a Recipe</link>" - section earlier in the manual. - </para> - </section> - - <section id='kernel-types'> - <title>Kernel Types</title> - - <para> - A kernel type defines a high-level kernel policy by - aggregating non-hardware configuration fragments with - patches you want to use when building a Linux kernel of a - specific type (e.g. a real-time kernel). - Syntactically, kernel types are no different than features - as described in the "<link linkend='features'>Features</link>" - section. - The - <ulink url='&YOCTO_DOCS_REF_URL;#var-LINUX_KERNEL_TYPE'><filename>LINUX_KERNEL_TYPE</filename></ulink> - variable in the kernel recipe selects the kernel type. - For example, in the <filename>linux-yocto_4.12.bb</filename> - kernel recipe found in - <filename>poky/meta/recipes-kernel/linux</filename>, a - <ulink url='&YOCTO_DOCS_BB_URL;#require-inclusion'><filename>require</filename></ulink> - directive includes the - <filename>poky/meta/recipes-kernel/linux/linux-yocto.inc</filename> - file, which has the following statement that defines the default - kernel type: - <literallayout class='monospaced'> - LINUX_KERNEL_TYPE ??= "standard" - </literallayout> - </para> - - <para> - Another example would be the real-time kernel (i.e. - <filename>linux-yocto-rt_4.12.bb</filename>). - This kernel recipe directly sets the kernel type as follows: - <literallayout class='monospaced'> - LINUX_KERNEL_TYPE = "preempt-rt" - </literallayout> - <note> - You can find kernel recipes in the - <filename>meta/recipes-kernel/linux</filename> directory of the - <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink> - (e.g. <filename>poky/meta/recipes-kernel/linux/linux-yocto_4.12.bb</filename>). - See the "<link linkend='using-kernel-metadata-in-a-recipe'>Using Kernel Metadata in a Recipe</link>" - section for more information. - </note> - </para> - - <para> - Three kernel types ("standard", "tiny", and "preempt-rt") are - supported for Linux Yocto kernels: - <itemizedlist> - <listitem><para>"standard": - Includes the generic Linux kernel policy of the Yocto - Project linux-yocto kernel recipes. - This policy includes, among other things, which file - systems, networking options, core kernel features, and - debugging and tracing options are supported. - </para></listitem> - <listitem><para>"preempt-rt": - Applies the <filename>PREEMPT_RT</filename> - patches and the configuration options required to - build a real-time Linux kernel. - This kernel type inherits from the "standard" kernel type. - </para></listitem> - <listitem><para>"tiny": - Defines a bare minimum configuration meant to serve as a - base for very small Linux kernels. - The "tiny" kernel type is independent from the "standard" - configuration. - Although the "tiny" kernel type does not currently include - any source changes, it might in the future. - </para></listitem> - </itemizedlist> - </para> - - <para> - For any given kernel type, the Metadata is defined by the - <filename>.scc</filename> (e.g. <filename>standard.scc</filename>). - Here is a partial listing for the <filename>standard.scc</filename> - file, which is found in the <filename>ktypes/standard</filename> - directory of the <filename>yocto-kernel-cache</filename> Git - repository: - <literallayout class='monospaced'> - # Include this kernel type fragment to get the standard features and - # configuration values. - - # Note: if only the features are desired, but not the configuration - # then this should be included as: - # include ktypes/standard/standard.scc nocfg - # if no chained configuration is desired, include it as: - # include ktypes/standard/standard.scc nocfg inherit - - - - include ktypes/base/base.scc - branch standard - - kconf non-hardware standard.cfg - - include features/kgdb/kgdb.scc - . - . - . - - include cfg/net/ip6_nf.scc - include cfg/net/bridge.scc - - include cfg/systemd.scc - - include features/rfkill/rfkill.scc - </literallayout> - </para> - - <para> - As with any <filename>.scc</filename> file, a - kernel type definition can aggregate other - <filename>.scc</filename> files with - <filename>include</filename> commands. - These definitions can also directly pull in - configuration fragments and patches with the - <filename>kconf</filename> and <filename>patch</filename> - commands, respectively. - </para> - - <note> - It is not strictly necessary to create a kernel type - <filename>.scc</filename> file. - The Board Support Package (BSP) file can implicitly define - the kernel type using a <filename>define - <ulink url='&YOCTO_DOCS_REF_URL;#var-KTYPE'>KTYPE</ulink> myktype</filename> - line. - See the "<link linkend='bsp-descriptions'>BSP Descriptions</link>" - section for more information. - </note> - </section> - - <section id='bsp-descriptions'> - <title>BSP Descriptions</title> - - <para> - BSP descriptions (i.e. <filename>*.scc</filename> files) - combine kernel types with hardware-specific features. - The hardware-specific Metadata is typically defined - independently in the BSP layer, and then aggregated with each - supported kernel type. - <note> - For BSPs supported by the Yocto Project, the BSP description - files are located in the <filename>bsp</filename> directory - of the - <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/yocto-kernel-cache/tree/bsp'><filename>yocto-kernel-cache</filename></ulink> - repository organized under the "Yocto Linux Kernel" heading - in the - <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi'>Yocto Project Source Repositories</ulink>. - </note> - </para> - - <para> - This section overviews the BSP description structure, the - aggregation concepts, and presents a detailed example using - a BSP supported by the Yocto Project (i.e. BeagleBone Board). - For complete information on BSP layer file hierarchy, see the - <ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>. - </para> - - <section id='bsp-description-file-overview'> - <title>Overview</title> - - <para> - For simplicity, consider the following root BSP layer - description files for the BeagleBone board. - These files employ both a structure and naming convention - for consistency. - The naming convention for the file is as follows: - <literallayout class='monospaced'> - <replaceable>bsp_root_name</replaceable>-<replaceable>kernel_type</replaceable>.scc - </literallayout> - Here are some example root layer BSP filenames for the - BeagleBone Board BSP, which is supported by the Yocto Project: - <literallayout class='monospaced'> - beaglebone-standard.scc - beaglebone-preempt-rt.scc - </literallayout> - Each file uses the root name (i.e "beaglebone") BSP name - followed by the kernel type. - </para> - - <para> - Examine the <filename>beaglebone-standard.scc</filename> - file: - <literallayout class='monospaced'> - define KMACHINE beaglebone - define KTYPE standard - define KARCH arm - - include ktypes/standard/standard.scc - branch beaglebone - - include beaglebone.scc - - # default policy for standard kernels - include features/latencytop/latencytop.scc - include features/profiling/profiling.scc - </literallayout> - Every top-level BSP description file should define the - <ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>, - <ulink url='&YOCTO_DOCS_REF_URL;#var-KTYPE'><filename>KTYPE</filename></ulink>, - and <ulink url='&YOCTO_DOCS_REF_URL;#var-KARCH'><filename>KARCH</filename></ulink> - variables. - These variables allow the OpenEmbedded build system to identify - the description as meeting the criteria set by the recipe being - built. - This example supports the "beaglebone" machine for the - "standard" kernel and the "arm" architecture. - </para> - - <para> - Be aware that a hard link between the - <filename>KTYPE</filename> variable and a kernel type - description file does not exist. - Thus, if you do not have the kernel type defined in your kernel - Metadata as it is here, you only need to ensure that the - <ulink url='&YOCTO_DOCS_REF_URL;#var-LINUX_KERNEL_TYPE'><filename>LINUX_KERNEL_TYPE</filename></ulink> - variable in the kernel recipe and the - <filename>KTYPE</filename> variable in the BSP description - file match. - </para> - - <para> - To separate your kernel policy from your hardware configuration, - you include a kernel type (<filename>ktype</filename>), such as - "standard". - In the previous example, this is done using the following: - <literallayout class='monospaced'> - include ktypes/standard/standard.scc - </literallayout> - This file aggregates all the configuration fragments, patches, - and features that make up your standard kernel policy. - See the "<link linkend='kernel-types'>Kernel Types</link>" - section for more information. - </para> - - <para> - To aggregate common configurations and features specific to the - kernel for <replaceable>mybsp</replaceable>, use the following: - <literallayout class='monospaced'> - include <replaceable>mybsp</replaceable>.scc - </literallayout> - You can see that in the BeagleBone example with the following: - <literallayout class='monospaced'> - include beaglebone.scc - </literallayout> - For information on how to break a complete - <filename>.config</filename> file into the various - configuration fragments, see the - "<link linkend='creating-config-fragments'>Creating Configuration Fragments</link>" - section. - </para> - - <para> - Finally, if you have any configurations specific to the - hardware that are not in a <filename>*.scc</filename> file, - you can include them as follows: - <literallayout class='monospaced'> - kconf hardware <replaceable>mybsp</replaceable>-<replaceable>extra</replaceable>.cfg - </literallayout> - The BeagleBone example does not include these types of - configurations. - However, the Malta 32-bit board does ("mti-malta32"). - Here is the <filename>mti-malta32-le-standard.scc</filename> - file: - <literallayout class='monospaced'> - define KMACHINE mti-malta32-le - define KMACHINE qemumipsel - define KTYPE standard - define KARCH mips - - include ktypes/standard/standard.scc - branch mti-malta32 - - include mti-malta32.scc - kconf hardware mti-malta32-le.cfg - </literallayout> - </para> - </section> - - <section id='bsp-description-file-example-minnow'> - <title>Example</title> - - <para> - Many real-world examples are more complex. - Like any other <filename>.scc</filename> file, BSP - descriptions can aggregate features. - Consider the Minnow BSP definition given the - <filename>linux-yocto-4.4</filename> branch of the - <filename>yocto-kernel-cache</filename> (i.e. - <filename>yocto-kernel-cache/bsp/minnow/minnow.scc</filename>): - <note> - Although the Minnow Board BSP is unused, the Metadata - remains and is being used here just as an example. - </note> - <literallayout class='monospaced'> - include cfg/x86.scc - include features/eg20t/eg20t.scc - include cfg/dmaengine.scc - include features/power/intel.scc - include cfg/efi.scc - include features/usb/ehci-hcd.scc - include features/usb/ohci-hcd.scc - include features/usb/usb-gadgets.scc - include features/usb/touchscreen-composite.scc - include cfg/timer/hpet.scc - include features/leds/leds.scc - include features/spi/spidev.scc - include features/i2c/i2cdev.scc - include features/mei/mei-txe.scc - - # Earlyprintk and port debug requires 8250 - kconf hardware cfg/8250.cfg - - kconf hardware minnow.cfg - kconf hardware minnow-dev.cfg - </literallayout> - </para> - - <para> - The <filename>minnow.scc</filename> description file includes - a hardware configuration fragment - (<filename>minnow.cfg</filename>) specific to the Minnow - BSP as well as several more general configuration - fragments and features enabling hardware found on the - machine. - This <filename>minnow.scc</filename> description file is then - included in each of the three - "minnow" description files for the supported kernel types - (i.e. "standard", "preempt-rt", and "tiny"). - Consider the "minnow" description for the "standard" kernel - type (i.e. <filename>minnow-standard.scc</filename>: - <literallayout class='monospaced'> - define KMACHINE minnow - define KTYPE standard - define KARCH i386 - - include ktypes/standard - - include minnow.scc - - # Extra minnow configs above the minimal defined in minnow.scc - include cfg/efi-ext.scc - include features/media/media-all.scc - include features/sound/snd_hda_intel.scc - - # The following should really be in standard.scc - # USB live-image support - include cfg/usb-mass-storage.scc - include cfg/boot-live.scc - - # Basic profiling - include features/latencytop/latencytop.scc - include features/profiling/profiling.scc - - # Requested drivers that don't have an existing scc - kconf hardware minnow-drivers-extra.cfg - </literallayout> - The <filename>include</filename> command midway through the file - includes the <filename>minnow.scc</filename> description that - defines all enabled hardware for the BSP that is common to - all kernel types. - Using this command significantly reduces duplication. - </para> - - <para> - Now consider the "minnow" description for the "tiny" kernel - type (i.e. <filename>minnow-tiny.scc</filename>): - <literallayout class='monospaced'> - define KMACHINE minnow - define KTYPE tiny - define KARCH i386 - - include ktypes/tiny - - include minnow.scc - </literallayout> - As you might expect, the "tiny" description includes quite a - bit less. - In fact, it includes only the minimal policy defined by the - "tiny" kernel type and the hardware-specific configuration - required for booting the machine along with the most basic - functionality of the system as defined in the base "minnow" - description file. - </para> - - <para> - Notice again the three critical variables: - <ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>, - <ulink url='&YOCTO_DOCS_REF_URL;#var-KTYPE'><filename>KTYPE</filename></ulink>, - and - <ulink url='&YOCTO_DOCS_REF_URL;#var-KARCH'><filename>KARCH</filename></ulink>. - Of these variables, only <filename>KTYPE</filename> - has changed to specify the "tiny" kernel type. - </para> - </section> - </section> -</section> - -<section id='kernel-metadata-location'> - <title>Kernel Metadata Location</title> - - <para> - Kernel Metadata always exists outside of the kernel tree either - defined in a kernel recipe (recipe-space) or outside of the recipe. - Where you choose to define the Metadata depends on what you want - to do and how you intend to work. - Regardless of where you define the kernel Metadata, the syntax used - applies equally. - </para> - - <para> - If you are unfamiliar with the Linux kernel and only wish - to apply a configuration and possibly a couple of patches provided to - you by others, the recipe-space method is recommended. - This method is also a good approach if you are working with Linux kernel - sources you do not control or if you just do not want to maintain a - Linux kernel Git repository on your own. - For partial information on how you can define kernel Metadata in - the recipe-space, see the - "<link linkend='modifying-an-existing-recipe'>Modifying an Existing Recipe</link>" - section. - </para> - - <para> - Conversely, if you are actively developing a kernel and are already - maintaining a Linux kernel Git repository of your own, you might find - it more convenient to work with kernel Metadata kept outside the - recipe-space. - Working with Metadata in this area can make iterative development of - the Linux kernel more efficient outside of the BitBake environment. - </para> - - <section id='recipe-space-metadata'> - <title>Recipe-Space Metadata</title> - - <para> - When stored in recipe-space, the kernel Metadata files reside in a - directory hierarchy below - <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>. - For a linux-yocto recipe or for a Linux kernel recipe derived - by copying and modifying - <filename>oe-core/meta-skeleton/recipes-kernel/linux/linux-yocto-custom.bb</filename> - to a recipe in your layer, <filename>FILESEXTRAPATHS</filename> - is typically set to - <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-THISDIR'><filename>THISDIR</filename></ulink><filename>}/${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>. - See the "<link linkend='modifying-an-existing-recipe'>Modifying an Existing Recipe</link>" - section for more information. - </para> - - <para> - Here is an example that shows a trivial tree of kernel Metadata - stored in recipe-space within a BSP layer: - <literallayout class='monospaced'> - meta-<replaceable>my_bsp_layer</replaceable>/ - `-- recipes-kernel - `-- linux - `-- linux-yocto - |-- bsp-standard.scc - |-- bsp.cfg - `-- standard.cfg - </literallayout> - </para> - - <para> - When the Metadata is stored in recipe-space, you must take - steps to ensure BitBake has the necessary information to decide - what files to fetch and when they need to be fetched again. - It is only necessary to specify the <filename>.scc</filename> - files on the - <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>. - BitBake parses them and fetches any files referenced in the - <filename>.scc</filename> files by the <filename>include</filename>, - <filename>patch</filename>, or <filename>kconf</filename> commands. - Because of this, it is necessary to bump the recipe - <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink> - value when changing the content of files not explicitly listed - in the <filename>SRC_URI</filename>. - </para> - - <para> - If the BSP description is in recipe space, you cannot simply list - the <filename>*.scc</filename> in the <filename>SRC_URI</filename> - statement. - You need to use the following form from your kernel append file: - <literallayout class='monospaced'> - SRC_URI_append_<replaceable>myplatform</replaceable> = " \ - file://<replaceable>myplatform</replaceable>;type=kmeta;destsuffix=<replaceable>myplatform</replaceable> \ - " - </literallayout> - </para> - </section> - - <section id='metadata-outside-the-recipe-space'> - <title>Metadata Outside the Recipe-Space</title> - - <para> - When stored outside of the recipe-space, the kernel Metadata - files reside in a separate repository. - The OpenEmbedded build system adds the Metadata to the build as - a "type=kmeta" repository through the - <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink> - variable. - As an example, consider the following <filename>SRC_URI</filename> - statement from the <filename>linux-yocto_4.12.bb</filename> - kernel recipe: - <literallayout class='monospaced'> - SRC_URI = "git://git.yoctoproject.org/linux-yocto-4.12.git;name=machine;branch=${KBRANCH}; \ - git://git.yoctoproject.org/yocto-kernel-cache;type=kmeta;name=meta;branch=yocto-4.12;destsuffix=${KMETA}" - </literallayout> - <filename>${KMETA}</filename>, in this context, is simply used to - name the directory into which the Git fetcher places the Metadata. - This behavior is no different than any multi-repository - <filename>SRC_URI</filename> statement used in a recipe (e.g. - see the previous section). - </para> - - <para> - You can keep kernel Metadata in a "kernel-cache", which is a - directory containing configuration fragments. - As with any Metadata kept outside the recipe-space, you simply - need to use the <filename>SRC_URI</filename> statement with the - "type=kmeta" attribute. - Doing so makes the kernel Metadata available during the - configuration phase. - </para> - - <para> - If you modify the Metadata, you must not forget to update the - <filename>SRCREV</filename> statements in the kernel's recipe. - In particular, you need to update the - <filename>SRCREV_meta</filename> variable to match the commit in - the <filename>KMETA</filename> branch you wish to use. - Changing the data in these branches and not updating the - <filename>SRCREV</filename> statements to match will cause the - build to fetch an older commit. - </para> - </section> -</section> - -<section id='organizing-your-source'> - <title>Organizing Your Source</title> - - <para> - Many recipes based on the <filename>linux-yocto-custom.bb</filename> - recipe use Linux kernel sources that have only a single - branch - "master". - This type of repository structure is fine for linear development - supporting a single machine and architecture. - However, if you work with multiple boards and architectures, - a kernel source repository with multiple branches is more - efficient. - For example, suppose you need a series of patches for one board to boot. - Sometimes, these patches are works-in-progress or fundamentally wrong, - yet they are still necessary for specific boards. - In these situations, you most likely do not want to include these - patches in every kernel you build (i.e. have the patches as part of - the lone "master" branch). - It is situations like these that give rise to multiple branches used - within a Linux kernel sources Git repository. - </para> - - <para> - Repository organization strategies exist that maximize source reuse, - remove redundancy, and logically order your changes. - This section presents strategies for the following cases: - <itemizedlist> - <listitem><para>Encapsulating patches in a feature description - and only including the patches in the BSP descriptions of - the applicable boards.</para></listitem> - <listitem><para>Creating a machine branch in your - kernel source repository and applying the patches on that - branch only.</para></listitem> - <listitem><para>Creating a feature branch in your - kernel source repository and merging that branch into your - BSP when needed.</para></listitem> - </itemizedlist> - </para> - - <para> - The approach you take is entirely up to you - and depends on what works best for your development model. - </para> - - <section id='encapsulating-patches'> - <title>Encapsulating Patches</title> - - <para> - if you are reusing patches from an external tree and are not - working on the patches, you might find the encapsulated feature - to be appropriate. - Given this scenario, you do not need to create any branches in the - source repository. - Rather, you just take the static patches you need and encapsulate - them within a feature description. - Once you have the feature description, you simply include that into - the BSP description as described in the - "<link linkend='bsp-descriptions'>BSP Descriptions</link>" - section. - </para> - - <para> - You can find information on how to create patches and BSP - descriptions in the "<link linkend='patches'>Patches</link>" and - "<link linkend='bsp-descriptions'>BSP Descriptions</link>" - sections. - </para> - </section> - - <section id='machine-branches'> - <title>Machine Branches</title> - - <para> - When you have multiple machines and architectures to support, - or you are actively working on board support, it is more - efficient to create branches in the repository based on - individual machines. - Having machine branches allows common source to remain in the - "master" branch with any features specific to a machine stored - in the appropriate machine branch. - This organization method frees you from continually reintegrating - your patches into a feature. - </para> - - <para> - Once you have a new branch, you can set up your kernel Metadata - to use the branch a couple different ways. - In the recipe, you can specify the new branch as the - <filename>KBRANCH</filename> to use for the board as - follows: - <literallayout class='monospaced'> - KBRANCH = "mynewbranch" - </literallayout> - Another method is to use the <filename>branch</filename> command - in the BSP description: - <literallayout class='monospaced'> - mybsp.scc: - define KMACHINE mybsp - define KTYPE standard - define KARCH i386 - include standard.scc - - branch mynewbranch - - include mybsp-hw.scc - </literallayout> - </para> - - <para> - If you find yourself with numerous branches, you might consider - using a hierarchical branching system similar to what the - Yocto Linux Kernel Git repositories use: - <literallayout class='monospaced'> - <replaceable>common</replaceable>/<replaceable>kernel_type</replaceable>/<replaceable>machine</replaceable> - </literallayout> - </para> - - <para> - If you had two kernel types, "standard" and "small" for - instance, three machines, and <replaceable>common</replaceable> - as <filename>mydir</filename>, the branches in your - Git repository might look like this: - <literallayout class='monospaced'> - mydir/base - mydir/standard/base - mydir/standard/machine_a - mydir/standard/machine_b - mydir/standard/machine_c - mydir/small/base - mydir/small/machine_a - </literallayout> - </para> - - <para> - This organization can help clarify the branch relationships. - In this case, <filename>mydir/standard/machine_a</filename> - includes everything in <filename>mydir/base</filename> and - <filename>mydir/standard/base</filename>. - The "standard" and "small" branches add sources specific to those - kernel types that for whatever reason are not appropriate for the - other branches. - <note> - The "base" branches are an artifact of the way Git manages - its data internally on the filesystem: Git will not allow you - to use <filename>mydir/standard</filename> and - <filename>mydir/standard/machine_a</filename> because it - would have to create a file and a directory named "standard". - </note> - </para> - </section> - - <section id='feature-branches'> - <title>Feature Branches</title> - - <para> - When you are actively developing new features, it can be more - efficient to work with that feature as a branch, rather than - as a set of patches that have to be regularly updated. - The Yocto Project Linux kernel tools provide for this with - the <filename>git merge</filename> command. - </para> - - <para> - To merge a feature branch into a BSP, insert the - <filename>git merge</filename> command after any - <filename>branch</filename> commands: - <literallayout class='monospaced'> - mybsp.scc: - define KMACHINE mybsp - define KTYPE standard - define KARCH i386 - include standard.scc - - branch mynewbranch - git merge myfeature - - include mybsp-hw.scc - </literallayout> - </para> - </section> -</section> - -<section id='scc-reference'> - <title>SCC Description File Reference</title> - - <para> - This section provides a brief reference for the commands you can use - within an SCC description file (<filename>.scc</filename>): - <itemizedlist> - <listitem><para> - <filename>branch [ref]</filename>: - Creates a new branch relative to the current branch - (typically <filename>${KTYPE}</filename>) using - the currently checked-out branch, or "ref" if specified. - </para></listitem> - <listitem><para> - <filename>define</filename>: - Defines variables, such as - <ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>, - <ulink url='&YOCTO_DOCS_REF_URL;#var-KTYPE'><filename>KTYPE</filename></ulink>, - <ulink url='&YOCTO_DOCS_REF_URL;#var-KARCH'><filename>KARCH</filename></ulink>, - and - <ulink url='&YOCTO_DOCS_REF_URL;#var-KFEATURE_DESCRIPTION'><filename>KFEATURE_DESCRIPTION</filename></ulink>. - </para></listitem> - <listitem><para> - <filename>include SCC_FILE</filename>: - Includes an SCC file in the current file. - The file is parsed as if you had inserted it inline. - </para></listitem> - <listitem><para> - <filename>kconf [hardware|non-hardware] CFG_FILE</filename>: - Queues a configuration fragment for merging into the final - Linux <filename>.config</filename> file.</para></listitem> - <listitem><para> - <filename>git merge GIT_BRANCH</filename>: - Merges the feature branch into the current branch. - </para></listitem> - <listitem><para> - <filename>patch PATCH_FILE</filename>: - Applies the patch to the current Git branch. - </para></listitem> - </itemizedlist> - </para> -</section> - -</chapter> -<!-- -vim: expandtab tw=80 ts=4 ---> |