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kernel-dev: Edits to the introduction chapter.
I did some re-writing for better understanding based on what I know. (From yocto-docs rev: fc3adb037ac07a90dfbba6b76643391480e0bce5) Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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Scott Rifenbark
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Richard Purdie
Richard Purdie
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@@ -7,14 +7,14 @@
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<title>Working with Advanced Metadata</title>
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<para>
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In addition to configuration fragments and patches, the
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Yocto Project kernel tools support rich metadata that you can
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use to define complex policies and BSP support.
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The purpose of the metadata and the tools to manage it, known as
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In addition to supporting configuration fragments and patches, the
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Yocto Project kernel tools also support rich
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<ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink> that you can
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use to define complex policies and Board Support Package (BSP) support.
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The purpose of the Metadata and the tools that manage it, known as
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the kern-tools (<filename>kern-tools-native_git.bb</filename>), is
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to assist in managing the complexity of the configuration and sources
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in support of multiple Board Support Packages (BSPs) and Linux kernel
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types.
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to help you manage the complexity of the configuration and sources
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used to support multiple BSPs and Linux kernel types.
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</para>
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<para>
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@@ -602,7 +602,7 @@ git repository:
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or <filename>meta/cfg/kernel-cache/</filename> if you are creating
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metadata in-tree as described in
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the "<link linkend='in-tree-metadata'>In-Tree Metadata</link>" section.
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</para>
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</para>
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<para>
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Original text:
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@@ -920,12 +920,12 @@ will want to specify in the KERNEL_FEATURES variable of the Linux kernel recipe
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<literallayout class='monospaced'>
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# Include this kernel type fragment to get the standard features and
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# configuration values.
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# Include all standard features
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include standard-nocfg.scc
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kconf non-hardware standard.cfg
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# individual cfg block section
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include cfg/fs/devtmpfs.scc
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include cfg/fs/debugfs.scc
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@@ -933,7 +933,7 @@ will want to specify in the KERNEL_FEATURES variable of the Linux kernel recipe
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include cfg/fs/ext2.scc
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include cfg/fs/ext3.scc
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include cfg/fs/ext4.scc
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include cfg/net/ipv6.scc
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include cfg/net/ip_nf.scc
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include cfg/net/ip6_nf.scc
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@@ -967,7 +967,7 @@ fragments together with any patches you want to use for all Linux kernel builds
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of the specified ktype. In short, ktypes are where you define a high-level
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kernel policy. Syntactically, however, they are no different than features (see
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3.3.3). preempt-rt, and tiny. The ktype is selected by the LINUX_KERNEL_TYPE
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variable in the recipe (see 3.1).
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variable in the recipe (see 3.1).
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By way of example, the linux-yocto-3.4 tree defines three ktypes: standard,
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tiny, and preempt-rt. The standard kernel type includes the generic Linux kernel
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@@ -983,12 +983,12 @@ not currently include any source changes, but it may in the future.
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The standard ktype is defined by standard.scc:
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# Include this kernel type fragment to get the standard features and
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# configuration values.
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# Include all standard features
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include standard-nocfg.scc
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kconf non-hardware standard.cfg
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# individual cfg block section
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include cfg/fs/devtmpfs.scc
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include cfg/fs/debugfs.scc
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@@ -996,7 +996,7 @@ The standard ktype is defined by standard.scc:
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include cfg/fs/ext2.scc
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include cfg/fs/ext3.scc
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include cfg/fs/ext4.scc
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include cfg/net/ipv6.scc
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include cfg/net/ip_nf.scc
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include cfg/net/ip6_nf.scc
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@@ -1092,7 +1092,7 @@ Note: It is not strictly necessary to create a ktype scc file. The BSP file can
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<literallayout class='monospaced'>
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fri2.scc:
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kconf hardware fri2.cfg
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include cfg/x86.scc
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include features/eg20t/eg20t.scc
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include cfg/dmaengine.scc
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@@ -1119,19 +1119,19 @@ Note: It is not strictly necessary to create a ktype scc file. The BSP file can
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define KMACHINE fri2
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define KTYPE standard
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define KARCH i386
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include ktypes/standard/standard.scc
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branch fri2
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git merge emgd-1.14
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include fri2.scc
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# Extra fri2 configs above the minimal defined in fri2.scc
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include cfg/efi-ext.scc
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include features/drm-emgd/drm-emgd.scc
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include cfg/vesafb.scc
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# default policy for standard kernels
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include cfg/usb-mass-storage.scc
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</literallayout>
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@@ -1162,10 +1162,10 @@ Note: It is not strictly necessary to create a ktype scc file. The BSP file can
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define KMACHINE fri2
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define KTYPE tiny
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define KARCH i386
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include ktypes/tiny/tiny.scc
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branch fri2
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include fri2.scc
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</literallayout>
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As you might expect, the tiny description includes quite a bit less.
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@@ -1236,7 +1236,7 @@ BSP definitions from the linux-yocto-3.4 repository:
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fri2.scc:
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kconf hardware fri2.cfg
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include cfg/x86.scc
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include features/eg20t/eg20t.scc
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include cfg/dmaengine.scc
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@@ -1257,19 +1257,19 @@ fri2-standard.scc:
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define KMACHINE fri2
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define KTYPE standard
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define KARCH i386
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include ktypes/standard/standard.scc
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branch fri2
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git merge emgd-1.14
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include fri2.scc
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# Extra fri2 configs above the minimal defined in fri2.scc
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include cfg/efi-ext.scc
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include features/drm-emgd/drm-emgd.scc
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include cfg/vesafb.scc
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# default policy for standard kernels
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include cfg/usb-mass-storage.scc
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@@ -1291,10 +1291,10 @@ fri2-tiny.scc:
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define KMACHINE fri2
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define KTYPE tiny
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define KARCH i386
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include ktypes/tiny/tiny.scc
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branch fri2
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include fri2.scc
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As you might expect, the tiny description includes quite a bit less. In fact,
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@@ -1435,9 +1435,9 @@ include them in the BSP description for the board(s) that require them (see
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Alternatively, you can create a branch in your Linux kernel sources and apply
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the patches there. You can then specify this new branch as the KBRANCH to use
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for this board. You can do this in the recipe with the KBRANCH variable:
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KBRANCH = "mynewbranch"
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or in the BSP description using the "branch" command:
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mybsp.scc:
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@@ -3,44 +3,69 @@
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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
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<chapter id='kernel-dev-intro'>
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<title>Introduction</title>
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<para>
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Regardless of how you intend to make use of the Yocto Project,
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chances are you are going to need to work with the Linux kernel.
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The Yocto Project provides a powerful set of tools for managing
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Linux kernel sources and configuration data.
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You can use this tooling to help you make a single configuration change,
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apply a couple of patches, or work with your own sources.
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</para>
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<para>
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The Yocto Project Kernel Development Manual describes common tasks
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you can perform using the kernel tooling as well as provides information
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about the metadata needed to work with the kernel inside the
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Yocto Project.
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</para>
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<section id='kernel-dev-background'>
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<title>Background</title>
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<section id='kernel-dev-overview'>
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<title>Overview</title>
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<para>
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Each Yocto Project release introduces a new set of linux-yocto
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kernel recipes that tracks the latest upstream developments and
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introduces newly supported platforms.
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In addition to the new kernel recipes, the previous recipes are
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refreshed and supported for at least one additional release.
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Regardless of how you intend to make use of the Yocto Project,
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chances are you will work with the Linux kernel.
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This manual provides background information on the Yocto Linux kernel
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<ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>,
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describes common tasks you can perform using the kernel tools,
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and shows you how to use the Metadata needed to work with
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the kernel inside the Yocto Project.
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</para>
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<para>
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Each Yocto Project release has a set of linux-yocto recipes, whose
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Git repositories you can view in the Yocto
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<ulink url='&YOCTO_GIT_URL;'>Source Repositories</ulink> under
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the "Yocto Linux Kernel" heading.
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New recipes for the release track the latest upstream developments
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and introduce newly supported platforms.
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Previous recipes in the release are refreshed and supported for at
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least one additional release.
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As they align, these previous releases are updated to include the
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latest from the Long Term Support Initiative (LTSI) project.
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Besides these recipes, a <filename>linux-yocto-dev.bb</filename>
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recipe is available for working with the very latest in upstream
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Linux kernel development as well as metadata development.
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Also included is a linux-yocto development recipe
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(<filename>linux-yocto-dev.bb</filename>) should you want to work
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with the very latest in upstream Linux kernel development and
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Metadata development.
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</para>
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<para>
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The Yocto Project also provides a powerful set of kernel
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tools for managing Linux kernel sources and configuration data.
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You can use these tools to make a single configuration change,
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apply multiple patches, or work with your own kernel sources.
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</para>
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<para>
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In particular, the kernel tools allow you to generate configuration
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fragments that specify only what you must, and nothing more.
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Configuration fragments only need to contain the highest level
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visible <filename>CONFIG</filename> options as presented by the Linux
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kernel <filename>menuconfig</filename> system.
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Contrast this against a complete Linux kernel
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<filename>.config</filename>, which includes all the automatically
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selected <filename>CONFIG</filename> options.
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This efficiency reduces your maintenance effort and allows you
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to further separate your configuration in ways that make sense for
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your project.
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A common split separates policy and hardware.
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For example, all your kernels might support
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the <filename>proc</filename> and <filename>sys</filename> filesystems,
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but only specific boards require sound, USB, or specific drivers.
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Specifying these configurations individually allows you to aggregate
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them together as needed, but maintains them in only one place.
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Similar logic applies to separating source changes.
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</para>
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<para>
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If you do not maintain your own kernel sources and need to make
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only minimal changes to the sources, these recipes provide a
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only minimal changes to the sources, the released recipes provide a
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vetted base upon which to layer your changes.
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Doing so allows you to benefit from the continual kernel
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integration and testing performed during development of the
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@@ -50,8 +75,8 @@
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<para>
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If, instead, you have a very specific Linux kernel source tree
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and are unable to align with one of the many official linux-yocto
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releases, an alternative exists by which you can use the Yocto
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Project Linux kernel tools with your own sources.
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recipes, an alternative exists by which you can use the Yocto
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Project Linux kernel tools with your own kernel sources.
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</para>
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</section>
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@@ -61,7 +86,7 @@
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<para>
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The sections that follow provide instructions for completing
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specific Linux kernel development tasks.
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These instructions assume you are familiar with working with
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These instructions assume you are comfortable working with
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<ulink url='http://developer.berlios.de/projects/bitbake/'>BitBake</ulink>
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recipes and basic open-source development tools.
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Understanding these concepts will facilitate the process of working
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