From 8097a978cef998d82cc1e35e94b090b0c8bb264f Mon Sep 17 00:00:00 2001 From: Scott Rifenbark Date: Wed, 10 Jan 2018 11:36:56 -0800 Subject: dev-manual, ref-manual: Moved Wic Plug-In section to dev-manual Fixes [YOCTO #12370] I had a section on Wick Plug-Ins in the ref-manual in the "technical details" chapter. This section has been combined with the section on using Wic that lives in the dev-manual. This move creates a single section on using Wic to create Wic-partitioned images. The section was moved out of the ref-manual and merged into the dev-manual Wic section. (From yocto-docs rev: 8724049141c9a793312dcf5ff5c3425948d1cbd0) Signed-off-by: Scott Rifenbark Signed-off-by: Richard Purdie --- .../dev-manual/dev-manual-common-tasks.xml | 213 ++++++++++++++++++++- 1 file changed, 209 insertions(+), 4 deletions(-) (limited to 'documentation/dev-manual') diff --git a/documentation/dev-manual/dev-manual-common-tasks.xml b/documentation/dev-manual/dev-manual-common-tasks.xml index 58bb6012ce..78825c7f1e 100644 --- a/documentation/dev-manual/dev-manual-common-tasks.xml +++ b/documentation/dev-manual/dev-manual-common-tasks.xml @@ -4878,16 +4878,17 @@ customized images, and as such, was designed to be completely extensible through a plug-in interface. See the - "Wic Plug-Ins Interface" - section in the Yocto Project Reference Manual for information - on these plug-ins. + "Using the Wic Plug-Ins Interface" + section for information on these plug-ins. This section provides some background information on Wic, describes what you need to have in place to run the tool, provides instruction on how to use - the Wic utility, and provides several examples. + the Wic utility, provides information on using the Wic plug-ins + interface, and provides several examples that show how to use + Wic.
@@ -5265,6 +5266,210 @@
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+ Using the Wic Plug-Ins Interface + + + You can extend and specialize Wic functionality by using + Wic plug-ins. + This section explains the Wic plug-in interface. + + Wic plug-ins consist of "source" and "imager" plug-ins. + Imager plug-ins are beyond the scope of this section. + + + + + Source plug-ins provide a mechanism to customize partition + content during the Wic image generation process. + You can use source plug-ins to map values that you specify + using --source commands in kickstart + files (i.e. *.wks) to a plug-in + implementation used to populate a given partition. + + If you use plug-ins that have build-time dependencies + (e.g. native tools, bootloaders, and so forth) + when building a Wic image, you need to specify those + dependencies using the + WKS_FILE_DEPENDS + variable. + + + + + Source plug-ins are subclasses defined in plug-in files. + As shipped, the Yocto Project provides several plug-in + files. + You can see the source plug-in files that ship with the + Yocto Project + here. + Each of these plug-in files contains source plug-ins that + are designed to populate a specific Wic image partition. + + + + Source plug-ins are subclasses of the + SourcePlugin class, which is + defined in the + poky/scripts/lib/wic/pluginbase.py + file. + For example, the BootimgEFIPlugin + source plug-in found in the + bootimg-efi.py file is a subclass of + the SourcePlugin class, which is found + in the pluginbase.py file. + + + + You can also implement source plug-ins in a layer outside + of the Source Repositories (external layer). + To do so, be sure that your plug-in files are located in + a directory whose path is + scripts/lib/wic/plugins/source/ + within your external layer. + When the plug-in files are located there, the source + plug-ins they contain are made available to Wic. + + + + When the Wic implementation needs to invoke a + partition-specific implementation, it looks for the plug-in + with the same name as the --source + parameter used in the kickstart file given to that + partition. + For example, if the partition is set up using the following + command in a kickstart file: + + part /boot --source bootimg-pcbios --ondisk sda --label boot --active --align 1024 + + The methods defined as class members of the matching + source plug-in (i.e. bootimg-pcbios) + in the bootimg-pcbios.py plug-in file + are used. + + + + To be more concrete, here is the corresponding plug-in + definition from the bootimg-pcbios.py + file for the previous command along with an example + method called by the Wic implementation when it needs to + prepare a partition using an implementation-specific + function: + + bootimg-pcbios.py + . + . + . + class BootimgPcbiosPlugin(SourcePlugin): + """ + Create MBR boot partition and install syslinux on it. + """ + + name = 'bootimg-pcbios' + . + . + . + @classmethod + def do_prepare_partition(cls, part, source_params, creator, cr_workdir, + oe_builddir, bootimg_dir, kernel_dir, + rootfs_dir, native_sysroot): + """ + Called to do the actual content population for a partition i.e. it + 'prepares' the partition to be incorporated into the image. + In this case, prepare content for legacy bios boot partition. + """ + . + . + . + + If a subclass (plug-in) itself does not implement a + particular function, Wic locates and uses the default + version in the superclass. + It is for this reason that all source plug-ins are derived + from the SourcePlugin class. + + + + The SourcePlugin class defined in + the pluginbase.py file defines + a set of methods that source plug-ins can implement or + override. + Any plug-ins (subclass of + SourcePlugin) that do not implement + a particular method inherit the implementation of the + method from the SourcePlugin class. + For more information, see the + SourcePlugin class in the + pluginbase.py file for details: + + + + The following list describes the methods implemented in the + SourcePlugin class: + + + do_prepare_partition(): + Called to populate a partition with actual content. + In other words, the method prepares the final + partition image that is incorporated into the + disk image. + + + do_configure_partition(): + Called before + do_prepare_partition() to + create custom configuration files for a partition + (e.g. syslinux or grub configuration files). + + + do_install_disk(): + Called after all partitions have been prepared and + assembled into a disk image. + This method provides a hook to allow finalization + of a disk image (e.g. writing an MBR). + + + do_stage_partition(): + Special content-staging hook called before + do_prepare_partition(). + This method is normally empty. + + Typically, a partition just uses the passed-in + parameters (e.g. the unmodified value of + bootimg_dir). + However, in some cases, things might need to be + more tailored. + As an example, certain files might additionally + need to be taken from + bootimg_dir + /boot. + This hook allows those files to be staged in a + customized fashion. + + get_bitbake_var() + allows you to access non-standard variables + that you might want to use for this + behavior. + + + + + + + You can extend the source plug-in mechanism. + To add more hooks, create more source plug-in methods + within SourcePlugin and the + corresponding derived subclasses. + The code that calls the plug-in methods uses the + plugin.get_source_plugin_methods() + function to find the method or methods needed by the call. + Retrieval of those methods is accomplished by filling up + a dict with keys that contain the method names of interest. + On success, these will be filled in with the actual + methods. + See the Wic implementation for examples and details. + +
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