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diff --git a/documentation/kernel-dev/advanced.rst b/documentation/kernel-dev/advanced.rst index b0d03851b3..4c463503f6 100644 --- a/documentation/kernel-dev/advanced.rst +++ b/documentation/kernel-dev/advanced.rst @@ -21,7 +21,7 @@ is the ``yocto-kernel-cache`` Git repository. You can find this repository grouped under the "Yocto Linux Kernel" heading in the :yocto_git:`Yocto Project Source Repositories <>`. -Kernel development tools ("kern-tools") exist also in the Yocto Project +Kernel development tools ("kern-tools") are also available in the Yocto Project Source Repositories under the "Yocto Linux Kernel" heading in the ``yocto-kernel-tools`` Git repository. The recipe that builds these tools is ``meta/recipes-kernel/kern-tools/kern-tools-native_git.bb`` in @@ -46,15 +46,15 @@ linux-yocto recipe. Every linux-yocto style recipe must define the :term:`KMACHINE` variable. This -variable is typically set to the same value as the ``MACHINE`` variable, +variable is typically set to the same value as the :term:`MACHINE` variable, which is used by :term:`BitBake`. However, in some cases, the variable might instead refer to the -underlying platform of the ``MACHINE``. +underlying platform of the :term:`MACHINE`. -Multiple BSPs can reuse the same ``KMACHINE`` name if they are built +Multiple BSPs can reuse the same :term:`KMACHINE` name if they are built using the same BSP description. Multiple Corei7-based BSPs could share -the same "intel-corei7-64" value for ``KMACHINE``. It is important to -realize that ``KMACHINE`` is just for kernel mapping, while ``MACHINE`` +the same "intel-corei7-64" value for :term:`KMACHINE`. It is important to +realize that :term:`KMACHINE` is just for kernel mapping, while :term:`MACHINE` is the machine type within a BSP Layer. Even with this distinction, however, these two variables can hold the same value. See the ":ref:`kernel-dev/advanced:bsp descriptions`" section for more information. @@ -66,11 +66,10 @@ to indicate the branch. .. note:: - You can use the ``KBRANCH`` value to define an alternate branch typically + You can use the :term:`KBRANCH` value to define an alternate branch typically with a machine override as shown here from the ``meta-yocto-bsp`` layer:: - KBRANCH_edgerouter = "standard/edgerouter" - + KBRANCH:beaglebone-yocto = "standard/beaglebone" The linux-yocto style recipes can optionally define the following variables: @@ -81,8 +80,8 @@ variables: :term:`LINUX_KERNEL_TYPE` defines the kernel type to be used in assembling the configuration. If -you do not specify a ``LINUX_KERNEL_TYPE``, it defaults to "standard". -Together with ``KMACHINE``, ``LINUX_KERNEL_TYPE`` defines the search +you do not specify a :term:`LINUX_KERNEL_TYPE`, it defaults to "standard". +Together with :term:`KMACHINE`, :term:`LINUX_KERNEL_TYPE` 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 @@ -90,21 +89,21 @@ configuration. The linux-yocto recipes define "standard", "tiny", and section for more information on kernel types. During the build, the kern-tools search for the BSP description file -that most closely matches the ``KMACHINE`` and ``LINUX_KERNEL_TYPE`` +that most closely matches the :term:`KMACHINE` and :term:`LINUX_KERNEL_TYPE` variables passed in from the recipe. The tools use the first BSP description they find that matches both variables. If the tools cannot find a match, they issue a warning. -The tools first search for the ``KMACHINE`` and then for the -``LINUX_KERNEL_TYPE``. If the tools cannot find a partial match, they -will use the sources from the ``KBRANCH`` and any configuration +The tools first search for the :term:`KMACHINE` and then for the +:term:`LINUX_KERNEL_TYPE`. If the tools cannot find a partial match, they +will use the sources from the :term:`KBRANCH` and any configuration specified in the :term:`SRC_URI`. You can use the :term:`KERNEL_FEATURES` variable to include features (configuration fragments, patches, or both) -that are not already included by the ``KMACHINE`` and -``LINUX_KERNEL_TYPE`` variable combination. For example, to include a +that are not already included by the :term:`KMACHINE` and +:term:`LINUX_KERNEL_TYPE` variable combination. For example, to include a feature specified as "features/netfilter/netfilter.scc", specify:: KERNEL_FEATURES += "features/netfilter/netfilter.scc" @@ -113,10 +112,10 @@ To include a feature called "cfg/sound.scc" just for the ``qemux86`` machine, specify:: - KERNEL_FEATURES_append_qemux86 = " cfg/sound.scc" + KERNEL_FEATURES:append:qemux86 = " cfg/sound.scc" The value of -the entries in ``KERNEL_FEATURES`` are dependent on their location +the entries in :term:`KERNEL_FEATURES` are dependent on their location within the kernel Metadata itself. The examples here are taken from the ``yocto-kernel-cache`` repository. Each branch of this repository contains "features" and "cfg" subdirectories at the top-level. For more @@ -183,7 +182,7 @@ the structure: order to define a base kernel policy or major kernel type to be reused across multiple BSPs, place the file in ``ktypes`` directory. -These distinctions can easily become blurred - especially as out-of-tree +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 @@ -304,8 +303,8 @@ The following listings show the ``build.scc`` file and part of the . . . - char *dump_write = NULL, *files_source = NULL; - int opt; + char *dump_write = NULL, *files_source = NULL; + int opt; -- 2.10.1 @@ -313,7 +312,7 @@ The following listings show the ``build.scc`` file and part of the The description file can include multiple patch statements where each statement handles a single -patch. In the example ``build.scc`` file, five patch statements exist +patch. In the example ``build.scc`` file, there are five patch statements for the five patches in the directory. You can create a typical ``.patch`` file using ``diff -Nurp`` or @@ -344,7 +343,7 @@ as how an additional feature description file is included with the 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 ``KERNEL_FEATURES`` variable of the +of things you want to specify in the :term:`KERNEL_FEATURES` variable of the Linux kernel recipe. See the ":ref:`kernel-dev/advanced:using kernel metadata in a recipe`" section earlier in the manual. @@ -352,17 +351,15 @@ in the manual. Kernel Types ------------ -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 ":ref:`kernel-dev/advanced:features`" section. The -:term:`LINUX_KERNEL_TYPE` -variable in the kernel recipe selects the kernel type. For example, in -the ``linux-yocto_4.12.bb`` kernel recipe found in -``poky/meta/recipes-kernel/linux``, a -:ref:`require <bitbake:bitbake-user-manual/bitbake-user-manual-metadata:\`\`require\`\` directive>` directive -includes the ``poky/meta/recipes-kernel/linux/linux-yocto.inc`` file, +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 +":ref:`kernel-dev/advanced:features`" section. The :term:`LINUX_KERNEL_TYPE` +variable in the kernel recipe selects the kernel type. For example, in the +``linux-yocto_4.12.bb`` kernel recipe found in ``poky/meta/recipes-kernel/linux``, a +:ref:`require <bitbake-user-manual/bitbake-user-manual-metadata:\`\`require\`\` directive>` +directive includes the ``poky/meta/recipes-kernel/linux/linux-yocto.inc`` file, which has the following statement that defines the default kernel type:: LINUX_KERNEL_TYPE ??= "standard" @@ -509,12 +506,12 @@ 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. -Be aware that a hard link between the ``KTYPE`` variable and a kernel -type description file does not exist. Thus, if you do not have the +Be aware that there is no hard link between the :term:`KTYPE` variable and a kernel +type description file. 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 :term:`LINUX_KERNEL_TYPE` -variable in the kernel recipe and the ``KTYPE`` variable in the BSP +variable in the kernel recipe and the :term:`KTYPE` variable in the BSP description file match. To separate your kernel policy from your hardware configuration, you @@ -566,15 +563,7 @@ Example Many real-world examples are more complex. Like any other ``.scc`` file, BSP descriptions can aggregate features. Consider the Minnow BSP definition given the ``linux-yocto-4.4`` branch of the -``yocto-kernel-cache`` (i.e. -``yocto-kernel-cache/bsp/minnow/minnow.scc``): - -.. note:: - - Although the Minnow Board BSP is unused, the Metadata remains and is - being used here just as an example. - -:: +``yocto-kernel-cache`` (i.e. ``yocto-kernel-cache/bsp/minnow/minnow.scc``):: include cfg/x86.scc include features/eg20t/eg20t.scc @@ -597,6 +586,11 @@ definition given the ``linux-yocto-4.4`` branch of the kconf hardware minnow.cfg kconf hardware minnow-dev.cfg +.. note:: + + Although the Minnow Board BSP is unused, the Metadata remains and is + being used here just as an example. + The ``minnow.scc`` description file includes a hardware configuration fragment (``minnow.cfg``) specific to the Minnow BSP as well as several more general configuration fragments and features enabling hardware @@ -657,7 +651,7 @@ Notice again the three critical variables: :term:`KMACHINE`, :term:`KTYPE`, and :term:`KARCH`. Of these variables, only -``KTYPE`` has changed to specify the "tiny" kernel type. +:term:`KTYPE` has changed to specify the "tiny" kernel type. Kernel Metadata Location ======================== @@ -688,12 +682,11 @@ Recipe-Space Metadata --------------------- When stored in recipe-space, the kernel Metadata files reside in a -directory hierarchy below -:term:`FILESEXTRAPATHS`. For -a linux-yocto recipe or for a Linux kernel recipe derived by copying and -modifying -``oe-core/meta-skeleton/recipes-kernel/linux/linux-yocto-custom.bb`` to -a recipe in your layer, ``FILESEXTRAPATHS`` is typically set to +directory hierarchy below :term:`FILESEXTRAPATHS`. For +a linux-yocto recipe or for a Linux kernel recipe derived by copying +:oe_git:`meta-skeleton/recipes-kernel/linux/linux-yocto-custom.bb +</openembedded-core/tree/meta-skeleton/recipes-kernel/linux/linux-yocto-custom.bb>` +into your layer and modifying it, :term:`FILESEXTRAPATHS` is typically set to ``${``\ :term:`THISDIR`\ ``}/${``\ :term:`PN`\ ``}``. See the ":ref:`kernel-dev/common:modifying an existing recipe`" section for more information. @@ -718,13 +711,13 @@ and fetches any files referenced in the ``.scc`` files by the ``include``, ``patch``, or ``kconf`` commands. Because of this, it is necessary to bump the recipe :term:`PR` value when changing the content of files not explicitly listed in the -``SRC_URI``. +:term:`SRC_URI`. If the BSP description is in recipe space, you cannot simply list the -``*.scc`` in the ``SRC_URI`` statement. You need to use the following +``*.scc`` in the :term:`SRC_URI` statement. You need to use the following form from your kernel append file:: - SRC_URI_append_myplatform = " \ + SRC_URI:append:myplatform = " \ file://myplatform;type=kmeta;destsuffix=myplatform \ " @@ -735,36 +728,35 @@ 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 :term:`SRC_URI` variable. As an -example, consider the following ``SRC_URI`` statement from the -``linux-yocto_4.12.bb`` kernel recipe:: - - 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}" +example, consider the following :term:`SRC_URI` statement from the +``linux-yocto_5.15.bb`` kernel recipe:: + SRC_URI = "git://git.yoctoproject.org/linux-yocto.git;name=machine;branch=${KBRANCH};protocol=https \ + git://git.yoctoproject.org/yocto-kernel-cache;type=kmeta;name=meta;branch=yocto-5.15;destsuffix=${KMETA};protocol=https" ``${KMETA}``, 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 ``SRC_URI`` statement used in a recipe (e.g. +than any multi-repository :term:`SRC_URI` statement used in a recipe (e.g. see the previous section). 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 ``SRC_URI`` statement with +the recipe-space, you simply need to use the :term:`SRC_URI` statement with the "type=kmeta" attribute. Doing so makes the kernel Metadata available during the configuration phase. -If you modify the Metadata, you must not forget to update the ``SRCREV`` +If you modify the Metadata, you must not forget to update the :term:`SRCREV` statements in the kernel's recipe. In particular, you need to update the ``SRCREV_meta`` variable to match the commit in the ``KMETA`` branch you wish to use. Changing the data in these branches and not updating the -``SRCREV`` statements to match will cause the build to fetch an older +:term:`SRCREV` statements to match will cause the build to fetch an older commit. Organizing Your Source ====================== Many recipes based on the ``linux-yocto-custom.bb`` recipe use Linux -kernel sources that have only a single branch - "master". This type of +kernel sources that have only a single branch. 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 @@ -773,11 +765,11 @@ 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 +default branch). It is situations like these that give rise to multiple branches used within a Linux kernel sources Git repository. -Repository organization strategies exist that maximize source reuse, -remove redundancy, and logically order your changes. This section +Here are repository organization strategies maximizing source reuse, +removing redundancy, and logically ordering your changes. This section presents strategies for the following cases: - Encapsulating patches in a feature description and only including the @@ -813,14 +805,14 @@ Machine Branches 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 +branches allows common source to remain in the development 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. 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 ``KBRANCH`` to use for the board as follows:: +new branch as the :term:`KBRANCH` to use for the board as follows:: KBRANCH = "mynewbranch" |