From c527fd1f14c27855a37f2e8ac5346ce8d940ced2 Mon Sep 17 00:00:00 2001 From: Tudor Florea Date: Thu, 16 Oct 2014 03:05:19 +0200 Subject: initial commit for Enea Linux 4.0-140929 Migrated from the internal git server on the daisy-enea-point-release branch Signed-off-by: Tudor Florea --- documentation/kernel-dev/kernel-dev-maint-appx.xml | 220 +++++++++++++++++++++ 1 file changed, 220 insertions(+) create mode 100644 documentation/kernel-dev/kernel-dev-maint-appx.xml (limited to 'documentation/kernel-dev/kernel-dev-maint-appx.xml') diff --git a/documentation/kernel-dev/kernel-dev-maint-appx.xml b/documentation/kernel-dev/kernel-dev-maint-appx.xml new file mode 100644 index 0000000000..a7c144ff75 --- /dev/null +++ b/documentation/kernel-dev/kernel-dev-maint-appx.xml @@ -0,0 +1,220 @@ + %poky; ] > + + +Kernel Maintenance + +
+ Tree Construction + + This section describes construction of the Yocto Project kernel source repositories + as accomplished by the Yocto Project team to create kernel repositories. + These kernel repositories are found under the heading "Yocto Linux Kernel" at + &YOCTO_GIT_URL;/cgit.cgi + and can be shipped as part of a Yocto Project release. + The team creates these repositories by + compiling and executing the set of feature descriptions for every BSP + and feature in the product. + Those feature descriptions list all necessary patches, + configuration, branching, tagging and feature divisions found in a kernel. + Thus, the Yocto Project kernel repository (or tree) is built. + + + The existence of this tree allows you to access and clone a particular + Yocto Project kernel repository and use it to build images based on their configurations + and features. + + + You can find the files used to describe all the valid features and BSPs + in the Yocto Project kernel in any clone of the Yocto Project kernel source repository + Git tree. + For example, the following command clones the Yocto Project baseline kernel that + branched off of linux.org version 3.4: + + $ git clone git://git.yoctoproject.org/linux-yocto-3.4 + + For another example of how to set up a local Git repository of the Yocto Project + kernel files, see the + "Yocto Project Kernel" bulleted + item in the Yocto Project Development Manual. + + + Once you have cloned the kernel Git repository on your local machine, you can + switch to the meta branch within the repository. + Here is an example that assumes the local Git repository for the kernel is in + a top-level directory named linux-yocto-3.4: + + $ cd linux-yocto-3.4 + $ git checkout -b meta origin/meta + + Once you have checked out and switched to the meta branch, + you can see a snapshot of all the kernel configuration and feature descriptions that are + used to build that particular kernel repository. + These descriptions are in the form of .scc files. + + + You should realize, however, that browsing your local kernel repository + for feature descriptions and patches is not an effective way to determine what is in a + particular kernel branch. + Instead, you should use Git directly to discover the changes in a branch. + Using Git is an efficient and flexible way to inspect changes to the kernel. + + Ground up reconstruction of the complete kernel tree is an action only taken by the + Yocto Project team during an active development cycle. + When you create a clone of the kernel Git repository, you are simply making it + efficiently available for building and development. + + + + The following steps describe what happens when the Yocto Project Team constructs + the Yocto Project kernel source Git repository (or tree) found at + given the + introduction of a new top-level kernel feature or BSP. + These are the actions that effectively create the tree + that includes the new feature, patch or BSP: + + A top-level kernel feature is passed to the kernel build subsystem. + Normally, this feature is a BSP for a particular kernel type. + The file that describes the top-level feature is located by searching + these system directories: + + The in-tree kernel-cache directories, which are located + in meta/cfg/kernel-cache + Areas pointed to by SRC_URI statements + found in recipes + + For a typical build, the target of the search is a + feature description in an .scc file + whose name follows this format: + + <bsp_name>-<kernel_type>.scc + + + Once located, the feature description is either compiled into a simple script + of actions, or into an existing equivalent script that is already part of the + shipped kernel. + Extra features are appended to the top-level feature description. + These features can come from the + KERNEL_FEATURES + variable in recipes. + Each extra feature is located, compiled and appended to the script + as described in step three. + The script is executed to produce a series of meta-* + directories. + These directories are descriptions of all the branches, tags, patches and configurations that + need to be applied to the base Git repository to completely create the + source (build) branch for the new BSP or feature. + The base repository is cloned, and the actions + listed in the meta-* directories are applied to the + tree. + The Git repository is left with the desired branch checked out and any + required branching, patching and tagging has been performed. + + + + The kernel tree is now ready for developer consumption to be locally cloned, + configured, and built into a Yocto Project kernel specific to some target hardware. + The generated meta-* directories add to the kernel + as shipped with the Yocto Project release. + Any add-ons and configuration data are applied to the end of an existing branch. + The full repository generation that is found in the + official Yocto Project kernel repositories at + http://git.yoctoproject.org/cgit.cgi + is the combination of all supported boards and configurations. + The technique the Yocto Project team uses is flexible and allows for seamless + blending of an immutable history with additional patches specific to a + deployment. + Any additions to the kernel become an integrated part of the branches. + + +
+ +
+ Build Strategy + + + + + Once a local Git repository of the Yocto Project kernel exists on a development system, + you can consider the compilation phase of kernel development - building a kernel image. + Some prerequisites exist that are validated by the build process before compilation + starts: + + + + The + SRC_URI points + to the kernel Git repository. + A BSP build branch exists. + This branch has the following form: + + <kernel_type>/<bsp_name> + + + + + The OpenEmbedded build system makes sure these conditions exist before attempting compilation. + Other means, however, do exist, such as as bootstrapping a BSP. + + + + Before building a kernel, the build process verifies the tree + and configures the kernel by processing all of the + configuration "fragments" specified by feature descriptions in the .scc + files. + As the features are compiled, associated kernel configuration fragments are noted + and recorded in the meta-* series of directories in their compilation order. + The fragments are migrated, pre-processed and passed to the Linux Kernel + Configuration subsystem (lkc) as raw input in the form + of a .config file. + The lkc uses its own internal dependency constraints to do the final + processing of that information and generates the final .config file + that is used during compilation. + + + + Using the board's architecture and other relevant values from the board's template, + kernel compilation is started and a kernel image is produced. + + + + The other thing that you notice once you configure a kernel is that + the build process generates a build tree that is separate from your kernel's local Git + source repository tree. + This build tree has a name that uses the following form, where + ${MACHINE} is the metadata name of the machine (BSP) and "kernel_type" is one + of the Yocto Project supported kernel types (e.g. "standard"): + + linux-${MACHINE}-<kernel_type>-build + + + + + The existing support in the kernel.org tree achieves this + default functionality. + + + + This behavior means that all the generated files for a particular machine or BSP are now in + the build tree directory. + The files include the final .config file, all the .o + files, the .a files, and so forth. + Since each machine or BSP has its own separate + Build Directory + in its own separate branch + of the Git repository, you can easily switch between different builds. + +
+ + -- cgit v1.2.3-54-g00ecf