sphinx: initial sphinx support

This commit is autogenerated pandoc to generate an inital set
of reST files based on DocBook XML files.

A .rst file is generated for each .xml files in all manuals with this
command:

cd <manual>
for i in *.xml; do \
  pandoc -f docbook -t rst --shift-heading-level-by=-1 \
  $i -o $(basename $i .xml).rst \
done

The conversion was done with: pandoc 2.9.2.1-91 (Arch Linux).

Also created an initial top level index file for each document, and
added all 'books' to the top leve index.rst file.

The YP manuals layout is organized as:

Book
  Chapter
    Section
      Section
        Section

Sphinx uses section headers to create the document structure.
ReStructuredText defines sections headers like that:

   To break longer text up into sections, you use section headers. These
   are a single line of text (one or more words) with adornment: an
   underline alone, or an underline and an overline together, in dashes
   "-----", equals "======", tildes "~~~~~~" or any of the
   non-alphanumeric characters = - ` : ' " ~ ^ _ * + # < > that you feel
   comfortable with. An underline-only adornment is distinct from an
   overline-and-underline adornment using the same character. The
   underline/overline must be at least as long as the title text. Be
   consistent, since all sections marked with the same adornment style
   are deemed to be at the same level:

Let's define the following convention when converting from Docbook:

Book                => overline ===   (Title)
  Chapter           => overline ***   (1.)
    Section         => ====           (1.1)
      Section       => ----           (1.1.1)
        Section     => ~~~~           (1.1.1.1)
          Section   => ^^^^           (1.1.1.1.1)

During the conversion with pandoc, we used --shift-heading-level=-1 to
convert most of DocBook headings automatically. However with this
setting, the Chapter header was removed, so I added it back
manually. Without this setting all headings were off by one, which was
more difficult to manually fix.

At least with this change, we now have the same TOC with Sphinx and
DocBook.

(From yocto-docs rev: 3c73d64a476d4423ee4c6808c685fa94d88d7df8)

Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 1230 insertions, 0 deletions

diff --git a/documentation/sdk-manual/sdk-extensible.rst b/documentation/sdk-manual/sdk-extensible.rst
new file mode 100644
index 0000000000..db6bfb4394
--- /dev/null
+++ b/documentation/sdk-manual/sdk-extensible.rst
@@ -0,0 +1,1230 @@
+************************
+Using the Extensible SDK
+************************
+
+This chapter describes the extensible SDK and how to install it.
+Information covers the pieces of the SDK, how to install it, and
+presents a look at using the ``devtool`` functionality. The extensible
+SDK makes it easy to add new applications and libraries to an image,
+modify the source for an existing component, test changes on the target
+hardware, and ease integration into the rest of the `OpenEmbedded build
+system <&YOCTO_DOCS_REF_URL;#build-system-term>`__.
+
+.. note::
+
+   For a side-by-side comparison of main features supported for an
+   extensible SDK as compared to a standard SDK, see the "
+   Introduction
+   " section.
+
+In addition to the functionality available through ``devtool``, you can
+alternatively make use of the toolchain directly, for example from
+Makefile and Autotools. See the "`Using the SDK Toolchain
+Directly <#sdk-working-projects>`__" chapter for more information.
+
+.. _sdk-extensible-sdk-intro:
+
+Why use the Extensible SDK and What is in It?
+=============================================
+
+The extensible SDK provides a cross-development toolchain and libraries
+tailored to the contents of a specific image. You would use the
+Extensible SDK if you want a toolchain experience supplemented with the
+powerful set of ``devtool`` commands tailored for the Yocto Project
+environment.
+
+The installed extensible SDK consists of several files and directories.
+Basically, it contains an SDK environment setup script, some
+configuration files, an internal build system, and the ``devtool``
+functionality.
+
+.. _sdk-installing-the-extensible-sdk:
+
+Installing the Extensible SDK
+=============================
+
+The first thing you need to do is install the SDK on your `Build
+Host <&YOCTO_DOCS_REF_URL;#hardware-build-system-term>`__ by running the
+``*.sh`` installation script.
+
+You can download a tarball installer, which includes the pre-built
+toolchain, the ``runqemu`` script, the internal build system,
+``devtool``, and support files from the appropriate
+`toolchain <&YOCTO_TOOLCHAIN_DL_URL;>`__ directory within the Index of
+Releases. Toolchains are available for several 32-bit and 64-bit
+architectures with the ``x86_64`` directories, respectively. The
+toolchains the Yocto Project provides are based off the
+``core-image-sato`` and ``core-image-minimal`` images and contain
+libraries appropriate for developing against that image.
+
+The names of the tarball installer scripts are such that a string
+representing the host system appears first in the filename and then is
+immediately followed by a string representing the target architecture.
+An extensible SDK has the string "-ext" as part of the name. Following
+is the general form:
+poky-glibc-host_system-image_type-arch-toolchain-ext-release_version.sh
+Where: host_system is a string representing your development system:
+i686 or x86_64. image_type is the image for which the SDK was built:
+core-image-sato or core-image-minimal arch is a string representing the
+tuned target architecture: aarch64, armv5e, core2-64, i586, mips32r2,
+mips64, ppc7400, or cortexa8hf-neon release_version is a string
+representing the release number of the Yocto Project: DISTRO,
+DISTRO+snapshot For example, the following SDK installer is for a 64-bit
+development host system and a i586-tuned target architecture based off
+the SDK for ``core-image-sato`` and using the current DISTRO snapshot:
+poky-glibc-x86_64-core-image-sato-i586-toolchain-ext-DISTRO.sh
+
+.. note::
+
+   As an alternative to downloading an SDK, you can build the SDK
+   installer. For information on building the installer, see the "
+   Building an SDK Installer
+   " section.
+
+The SDK and toolchains are self-contained and by default are installed
+into the ``poky_sdk`` folder in your home directory. You can choose to
+install the extensible SDK in any location when you run the installer.
+However, because files need to be written under that directory during
+the normal course of operation, the location you choose for installation
+must be writable for whichever users need to use the SDK.
+
+The following command shows how to run the installer given a toolchain
+tarball for a 64-bit x86 development host system and a 64-bit x86 target
+architecture. The example assumes the SDK installer is located in
+``~/Downloads/`` and has execution rights.
+
+.. note::
+
+   If you do not have write permissions for the directory into which you
+   are installing the SDK, the installer notifies you and exits. For
+   that case, set up the proper permissions in the directory and run the
+   installer again.
+
+$
+./Downloads/poky-glibc-x86_64-core-image-minimal-core2-64-toolchain-ext-2.5.sh
+Poky (Yocto Project Reference Distro) Extensible SDK installer version
+2.5
+==========================================================================
+Enter target directory for SDK (default: ~/poky_sdk): You are about to
+install the SDK to "/home/scottrif/poky_sdk". Proceed [Y/n]? Y
+Extracting SDK..............done Setting it up... Extracting
+buildtools... Preparing build system... Parsing recipes: 100%
+\|##################################################################\|
+Time: 0:00:52 Initialising tasks: 100%
+\|###############################################################\|
+Time: 0:00:00 Checking sstate mirror object availability: 100%
+\|#######################################\| Time: 0:00:00 Loading cache:
+100%
+\|####################################################################\|
+Time: 0:00:00 Initialising tasks: 100%
+\|###############################################################\|
+Time: 0:00:00 done SDK has been successfully set up and is ready to be
+used. Each time you wish to use the SDK in a new shell session, you need
+to source the environment setup script e.g. $ .
+/home/scottrif/poky_sdk/environment-setup-core2-64-poky-linux
+
+.. _sdk-running-the-extensible-sdk-environment-setup-script:
+
+Running the Extensible SDK Environment Setup Script
+===================================================
+
+Once you have the SDK installed, you must run the SDK environment setup
+script before you can actually use the SDK. This setup script resides in
+the directory you chose when you installed the SDK, which is either the
+default ``poky_sdk`` directory or the directory you chose during
+installation.
+
+Before running the script, be sure it is the one that matches the
+architecture for which you are developing. Environment setup scripts
+begin with the string "``environment-setup``" and include as part of
+their name the tuned target architecture. As an example, the following
+commands set the working directory to where the SDK was installed and
+then source the environment setup script. In this example, the setup
+script is for an IA-based target machine using i586 tuning: $ cd
+/home/scottrif/poky_sdk $ source environment-setup-core2-64-poky-linux
+SDK environment now set up; additionally you may now run devtool to
+perform development tasks. Run devtool --help for further details.
+Running the setup script defines many environment variables needed in
+order to use the SDK (e.g. ``PATH``,
+```CC`` <&YOCTO_DOCS_REF_URL;#var-CC>`__,
+```LD`` <&YOCTO_DOCS_REF_URL;#var-LD>`__, and so forth). If you want to
+see all the environment variables the script exports, examine the
+installation file itself.
+
+Using ``devtool`` in Your SDK Workflow
+======================================
+
+The cornerstone of the extensible SDK is a command-line tool called
+``devtool``. This tool provides a number of features that help you
+build, test and package software within the extensible SDK, and
+optionally integrate it into an image built by the OpenEmbedded build
+system.
+
+.. note::
+
+   The use of
+   devtool
+   is not limited to the extensible SDK. You can use
+   devtool
+   to help you easily develop any project whose build output must be
+   part of an image built using the build system.
+
+The ``devtool`` command line is organized similarly to
+`Git <&YOCTO_DOCS_OM_URL;#git>`__ in that it has a number of
+sub-commands for each function. You can run ``devtool --help`` to see
+all the commands.
+
+.. note::
+
+   See the "
+   devtool
+    Quick Reference
+   " in the Yocto Project Reference Manual for a
+   devtool
+   quick reference.
+
+Three ``devtool`` subcommands exist that provide entry-points into
+development:
+
+-  *``devtool add``*: Assists in adding new software to be built.
+
+-  *``devtool modify``*: Sets up an environment to enable you to modify
+   the source of an existing component.
+
+-  *``devtool upgrade``*: Updates an existing recipe so that you can
+   build it for an updated set of source files.
+
+As with the build system, "recipes" represent software packages within
+``devtool``. When you use ``devtool add``, a recipe is automatically
+created. When you use ``devtool modify``, the specified existing recipe
+is used in order to determine where to get the source code and how to
+patch it. In both cases, an environment is set up so that when you build
+the recipe a source tree that is under your control is used in order to
+allow you to make changes to the source as desired. By default, new
+recipes and the source go into a "workspace" directory under the SDK.
+
+The remainder of this section presents the ``devtool add``,
+``devtool modify``, and ``devtool upgrade`` workflows.
+
+.. _sdk-use-devtool-to-add-an-application:
+
+Use ``devtool add`` to Add an Application
+-----------------------------------------
+
+The ``devtool add`` command generates a new recipe based on existing
+source code. This command takes advantage of the
+`workspace <&YOCTO_DOCS_REF_URL;#devtool-the-workspace-layer-structure>`__
+layer that many ``devtool`` commands use. The command is flexible enough
+to allow you to extract source code into both the workspace or a
+separate local Git repository and to use existing code that does not
+need to be extracted.
+
+Depending on your particular scenario, the arguments and options you use
+with ``devtool add`` form different combinations. The following diagram
+shows common development flows you would use with the ``devtool add``
+command:
+
+1. *Generating the New Recipe*: The top part of the flow shows three
+   scenarios by which you could use ``devtool add`` to generate a recipe
+   based on existing source code.
+
+   In a shared development environment, it is typical for other
+   developers to be responsible for various areas of source code. As a
+   developer, you are probably interested in using that source code as
+   part of your development within the Yocto Project. All you need is
+   access to the code, a recipe, and a controlled area in which to do
+   your work.
+
+   Within the diagram, three possible scenarios feed into the
+   ``devtool add`` workflow:
+
+   -  *Left*: The left scenario in the figure represents a common
+      situation where the source code does not exist locally and needs
+      to be extracted. In this situation, the source code is extracted
+      to the default workspace - you do not want the files in some
+      specific location outside of the workspace. Thus, everything you
+      need will be located in the workspace: $ devtool add recipe
+      fetchuri With this command, ``devtool`` extracts the upstream
+      source files into a local Git repository within the ``sources``
+      folder. The command then creates a recipe named recipe and a
+      corresponding append file in the workspace. If you do not provide
+      recipe, the command makes an attempt to determine the recipe name.
+
+   -  *Middle*: The middle scenario in the figure also represents a
+      situation where the source code does not exist locally. In this
+      case, the code is again upstream and needs to be extracted to some
+      local area - this time outside of the default workspace.
+
+      .. note::
+
+         If required,
+         devtool
+         always creates a Git repository locally during the extraction.
+
+      Furthermore, the first positional argument srctree in this case
+      identifies where the ``devtool add`` command will locate the
+      extracted code outside of the workspace. You need to specify an
+      empty directory: $ devtool add recipe srctree fetchuri In summary,
+      the source code is pulled from fetchuri and extracted into the
+      location defined by srctree as a local Git repository.
+
+      Within workspace, ``devtool`` creates a recipe named recipe along
+      with an associated append file.
+
+   -  *Right*: The right scenario in the figure represents a situation
+      where the srctree has been previously prepared outside of the
+      ``devtool`` workspace.
+
+      The following command provides a new recipe name and identifies
+      the existing source tree location: $ devtool add recipe srctree
+      The command examines the source code and creates a recipe named
+      recipe for the code and places the recipe into the workspace.
+
+      Because the extracted source code already exists, ``devtool`` does
+      not try to relocate the source code into the workspace - only the
+      new recipe is placed in the workspace.
+
+      Aside from a recipe folder, the command also creates an associated
+      append folder and places an initial ``*.bbappend`` file within.
+
+2. *Edit the Recipe*: You can use ``devtool edit-recipe`` to open up the
+   editor as defined by the ``$EDITOR`` environment variable and modify
+   the file: $ devtool edit-recipe recipe From within the editor, you
+   can make modifications to the recipe that take affect when you build
+   it later.
+
+3. *Build the Recipe or Rebuild the Image*: The next step you take
+   depends on what you are going to do with the new code.
+
+   If you need to eventually move the build output to the target
+   hardware, use the following ``devtool`` command: $ devtool build
+   recipe
+
+   On the other hand, if you want an image to contain the recipe's
+   packages from the workspace for immediate deployment onto a device
+   (e.g. for testing purposes), you can use the ``devtool build-image``
+   command: $ devtool build-image image
+
+4. *Deploy the Build Output*: When you use the ``devtool build`` command
+   to build out your recipe, you probably want to see if the resulting
+   build output works as expected on the target hardware.
+
+   .. note::
+
+      This step assumes you have a previously built image that is
+      already either running in QEMU or is running on actual hardware.
+      Also, it is assumed that for deployment of the image to the
+      target, SSH is installed in the image and, if the image is running
+      on real hardware, you have network access to and from your
+      development machine.
+
+   You can deploy your build output to that target hardware by using the
+   ``devtool deploy-target`` command: $ devtool deploy-target recipe
+   target The target is a live target machine running as an SSH server.
+
+   You can, of course, also deploy the image you build to actual
+   hardware by using the ``devtool build-image`` command. However,
+   ``devtool`` does not provide a specific command that allows you to
+   deploy the image to actual hardware.
+
+5. *Finish Your Work With the Recipe*: The ``devtool finish`` command
+   creates any patches corresponding to commits in the local Git
+   repository, moves the new recipe to a more permanent layer, and then
+   resets the recipe so that the recipe is built normally rather than
+   from the workspace. $ devtool finish recipe layer
+
+   .. note::
+
+      Any changes you want to turn into patches must be committed to the
+      Git repository in the source tree.
+
+   As mentioned, the ``devtool finish`` command moves the final recipe
+   to its permanent layer.
+
+   As a final process of the ``devtool finish`` command, the state of
+   the standard layers and the upstream source is restored so that you
+   can build the recipe from those areas rather than the workspace.
+
+   .. note::
+
+      You can use the
+      devtool reset
+      command to put things back should you decide you do not want to
+      proceed with your work. If you do use this command, realize that
+      the source tree is preserved.
+
+.. _sdk-devtool-use-devtool-modify-to-modify-the-source-of-an-existing-component:
+
+Use ``devtool modify`` to Modify the Source of an Existing Component
+--------------------------------------------------------------------
+
+The ``devtool modify`` command prepares the way to work on existing code
+that already has a local recipe in place that is used to build the
+software. The command is flexible enough to allow you to extract code
+from an upstream source, specify the existing recipe, and keep track of
+and gather any patch files from other developers that are associated
+with the code.
+
+Depending on your particular scenario, the arguments and options you use
+with ``devtool modify`` form different combinations. The following
+diagram shows common development flows for the ``devtool modify``
+command:
+
+1. *Preparing to Modify the Code*: The top part of the flow shows three
+   scenarios by which you could use ``devtool modify`` to prepare to
+   work on source files. Each scenario assumes the following:
+
+   -  The recipe exists locally in a layer external to the ``devtool``
+      workspace.
+
+   -  The source files exist either upstream in an un-extracted state or
+      locally in a previously extracted state.
+
+   The typical situation is where another developer has created a layer
+   for use with the Yocto Project and their recipe already resides in
+   that layer. Furthermore, their source code is readily available
+   either upstream or locally.
+
+   -  *Left*: The left scenario in the figure represents a common
+      situation where the source code does not exist locally and it
+      needs to be extracted from an upstream source. In this situation,
+      the source is extracted into the default ``devtool`` workspace
+      location. The recipe, in this scenario, is in its own layer
+      outside the workspace (i.e. ``meta-``\ layername).
+
+      The following command identifies the recipe and, by default,
+      extracts the source files: $ devtool modify recipe Once
+      ``devtool``\ locates the recipe, ``devtool`` uses the recipe's
+      ```SRC_URI`` <&YOCTO_DOCS_REF_URL;#var-SRC_URI>`__ statements to
+      locate the source code and any local patch files from other
+      developers.
+
+      With this scenario, no srctree argument exists. Consequently, the
+      default behavior of the ``devtool modify`` command is to extract
+      the source files pointed to by the ``SRC_URI`` statements into a
+      local Git structure. Furthermore, the location for the extracted
+      source is the default area within the ``devtool`` workspace. The
+      result is that the command sets up both the source code and an
+      append file within the workspace while the recipe remains in its
+      original location.
+
+      Additionally, if you have any non-patch local files (i.e. files
+      referred to with ``file://`` entries in ``SRC_URI`` statement
+      excluding ``*.patch/`` or ``*.diff``), these files are copied to
+      an ``oe-local-files`` folder under the newly created source tree.
+      Copying the files here gives you a convenient area from which you
+      can modify the files. Any changes or additions you make to those
+      files are incorporated into the build the next time you build the
+      software just as are other changes you might have made to the
+      source.
+
+   -  *Middle*: The middle scenario in the figure represents a situation
+      where the source code also does not exist locally. In this case,
+      the code is again upstream and needs to be extracted to some local
+      area as a Git repository. The recipe, in this scenario, is again
+      local and in its own layer outside the workspace.
+
+      The following command tells ``devtool`` the recipe with which to
+      work and, in this case, identifies a local area for the extracted
+      source files that exists outside of the default ``devtool``
+      workspace: $ devtool modify recipe srctree
+
+      .. note::
+
+         You cannot provide a URL for
+         srctree
+         using the
+         devtool
+         command.
+
+      As with all extractions, the command uses the recipe's ``SRC_URI``
+      statements to locate the source files and any associated patch
+      files. Non-patch files are copied to an ``oe-local-files`` folder
+      under the newly created source tree.
+
+      Once the files are located, the command by default extracts them
+      into srctree.
+
+      Within workspace, ``devtool`` creates an append file for the
+      recipe. The recipe remains in its original location but the source
+      files are extracted to the location you provide with srctree.
+
+   -  *Right*: The right scenario in the figure represents a situation
+      where the source tree (srctree) already exists locally as a
+      previously extracted Git structure outside of the ``devtool``
+      workspace. In this example, the recipe also exists elsewhere
+      locally in its own layer.
+
+      The following command tells ``devtool`` the recipe with which to
+      work, uses the "-n" option to indicate source does not need to be
+      extracted, and uses srctree to point to the previously extracted
+      source files: $ devtool modify -n recipe srctree
+
+      If an ``oe-local-files`` subdirectory happens to exist and it
+      contains non-patch files, the files are used. However, if the
+      subdirectory does not exist and you run the ``devtool finish``
+      command, any non-patch files that might exist next to the recipe
+      are removed because it appears to ``devtool`` that you have
+      deleted those files.
+
+      Once the ``devtool modify`` command finishes, it creates only an
+      append file for the recipe in the ``devtool`` workspace. The
+      recipe and the source code remain in their original locations.
+
+2. *Edit the Source*: Once you have used the ``devtool modify`` command,
+   you are free to make changes to the source files. You can use any
+   editor you like to make and save your source code modifications.
+
+3. *Build the Recipe or Rebuild the Image*: The next step you take
+   depends on what you are going to do with the new code.
+
+   If you need to eventually move the build output to the target
+   hardware, use the following ``devtool`` command: $ devtool build
+   recipe
+
+   On the other hand, if you want an image to contain the recipe's
+   packages from the workspace for immediate deployment onto a device
+   (e.g. for testing purposes), you can use the ``devtool build-image``
+   command: $ devtool build-image image
+
+4. *Deploy the Build Output*: When you use the ``devtool build`` command
+   to build out your recipe, you probably want to see if the resulting
+   build output works as expected on target hardware.
+
+   .. note::
+
+      This step assumes you have a previously built image that is
+      already either running in QEMU or running on actual hardware.
+      Also, it is assumed that for deployment of the image to the
+      target, SSH is installed in the image and if the image is running
+      on real hardware that you have network access to and from your
+      development machine.
+
+   You can deploy your build output to that target hardware by using the
+   ``devtool deploy-target`` command: $ devtool deploy-target recipe
+   target The target is a live target machine running as an SSH server.
+
+   You can, of course, use other methods to deploy the image you built
+   using the ``devtool build-image`` command to actual hardware.
+   ``devtool`` does not provide a specific command to deploy the image
+   to actual hardware.
+
+5. *Finish Your Work With the Recipe*: The ``devtool finish`` command
+   creates any patches corresponding to commits in the local Git
+   repository, updates the recipe to point to them (or creates a
+   ``.bbappend`` file to do so, depending on the specified destination
+   layer), and then resets the recipe so that the recipe is built
+   normally rather than from the workspace. $ devtool finish recipe
+   layer
+
+   .. note::
+
+      Any changes you want to turn into patches must be staged and
+      committed within the local Git repository before you use the
+      devtool finish
+      command.
+
+   Because there is no need to move the recipe, ``devtool finish``
+   either updates the original recipe in the original layer or the
+   command creates a ``.bbappend`` file in a different layer as provided
+   by layer. Any work you did in the ``oe-local-files`` directory is
+   preserved in the original files next to the recipe during the
+   ``devtool finish`` command.
+
+   As a final process of the ``devtool finish`` command, the state of
+   the standard layers and the upstream source is restored so that you
+   can build the recipe from those areas rather than from the workspace.
+
+   .. note::
+
+      You can use the
+      devtool reset
+      command to put things back should you decide you do not want to
+      proceed with your work. If you do use this command, realize that
+      the source tree is preserved.
+
+.. _sdk-devtool-use-devtool-upgrade-to-create-a-version-of-the-recipe-that-supports-a-newer-version-of-the-software:
+
+Use ``devtool upgrade`` to Create a Version of the Recipe that Supports a Newer Version of the Software
+-------------------------------------------------------------------------------------------------------
+
+The ``devtool upgrade`` command upgrades an existing recipe to that of a
+more up-to-date version found upstream. Throughout the life of software,
+recipes continually undergo version upgrades by their upstream
+publishers. You can use the ``devtool upgrade`` workflow to make sure
+your recipes you are using for builds are up-to-date with their upstream
+counterparts.
+
+.. note::
+
+   Several methods exist by which you can upgrade recipes -
+   devtool upgrade
+   happens to be one. You can read about all the methods by which you
+   can upgrade recipes in the "
+   Upgrading Recipes
+   " section of the Yocto Project Development Tasks Manual.
+
+The ``devtool upgrade`` command is flexible enough to allow you to
+specify source code revision and versioning schemes, extract code into
+or out of the ``devtool``
+`workspace <&YOCTO_DOCS_REF_URL;#devtool-the-workspace-layer-structure>`__,
+and work with any source file forms that the
+`fetchers <&YOCTO_DOCS_BB_URL;#bb-fetchers>`__ support.
+
+The following diagram shows the common development flow used with the
+``devtool upgrade`` command:
+
+1. *Initiate the Upgrade*: The top part of the flow shows the typical
+   scenario by which you use the ``devtool upgrade`` command. The
+   following conditions exist:
+
+   -  The recipe exists in a local layer external to the ``devtool``
+      workspace.
+
+   -  The source files for the new release exist in the same location
+      pointed to by ```SRC_URI`` <&YOCTO_DOCS_REF_URL;#var-SRC_URI>`__
+      in the recipe (e.g. a tarball with the new version number in the
+      name, or as a different revision in the upstream Git repository).
+
+   A common situation is where third-party software has undergone a
+   revision so that it has been upgraded. The recipe you have access to
+   is likely in your own layer. Thus, you need to upgrade the recipe to
+   use the newer version of the software: $ devtool upgrade -V version
+   recipe By default, the ``devtool upgrade`` command extracts source
+   code into the ``sources`` directory in the
+   `workspace <&YOCTO_DOCS_REF_URL;#devtool-the-workspace-layer-structure>`__.
+   If you want the code extracted to any other location, you need to
+   provide the srctree positional argument with the command as follows:
+   $ devtool upgrade -V version recipe srctree
+
+   .. note::
+
+      In this example, the "-V" option specifies the new version. If you
+      don't use "-V", the command upgrades the recipe to the latest
+      version.
+
+   If the source files pointed to by the ``SRC_URI`` statement in the
+   recipe are in a Git repository, you must provide the "-S" option and
+   specify a revision for the software.
+
+   Once ``devtool`` locates the recipe, it uses the ``SRC_URI`` variable
+   to locate the source code and any local patch files from other
+   developers. The result is that the command sets up the source code,
+   the new version of the recipe, and an append file all within the
+   workspace.
+
+   Additionally, if you have any non-patch local files (i.e. files
+   referred to with ``file://`` entries in ``SRC_URI`` statement
+   excluding ``*.patch/`` or ``*.diff``), these files are copied to an
+   ``oe-local-files`` folder under the newly created source tree.
+   Copying the files here gives you a convenient area from which you can
+   modify the files. Any changes or additions you make to those files
+   are incorporated into the build the next time you build the software
+   just as are other changes you might have made to the source.
+
+2. *Resolve any Conflicts created by the Upgrade*: Conflicts could exist
+   due to the software being upgraded to a new version. Conflicts occur
+   if your recipe specifies some patch files in ``SRC_URI`` that
+   conflict with changes made in the new version of the software. For
+   such cases, you need to resolve the conflicts by editing the source
+   and following the normal ``git rebase`` conflict resolution process.
+
+   Before moving onto the next step, be sure to resolve any such
+   conflicts created through use of a newer or different version of the
+   software.
+
+3. *Build the Recipe or Rebuild the Image*: The next step you take
+   depends on what you are going to do with the new code.
+
+   If you need to eventually move the build output to the target
+   hardware, use the following ``devtool`` command: $ devtool build
+   recipe
+
+   On the other hand, if you want an image to contain the recipe's
+   packages from the workspace for immediate deployment onto a device
+   (e.g. for testing purposes), you can use the ``devtool build-image``
+   command: $ devtool build-image image
+
+4. *Deploy the Build Output*: When you use the ``devtool build`` command
+   or ``bitbake`` to build your recipe, you probably want to see if the
+   resulting build output works as expected on target hardware.
+
+   .. note::
+
+      This step assumes you have a previously built image that is
+      already either running in QEMU or running on actual hardware.
+      Also, it is assumed that for deployment of the image to the
+      target, SSH is installed in the image and if the image is running
+      on real hardware that you have network access to and from your
+      development machine.
+
+   You can deploy your build output to that target hardware by using the
+   ``devtool deploy-target`` command: $ devtool deploy-target recipe
+   target The target is a live target machine running as an SSH server.
+
+   You can, of course, also deploy the image you build using the
+   ``devtool build-image`` command to actual hardware. However,
+   ``devtool`` does not provide a specific command that allows you to do
+   this.
+
+5. *Finish Your Work With the Recipe*: The ``devtool finish`` command
+   creates any patches corresponding to commits in the local Git
+   repository, moves the new recipe to a more permanent layer, and then
+   resets the recipe so that the recipe is built normally rather than
+   from the workspace.
+
+   Any work you did in the ``oe-local-files`` directory is preserved in
+   the original files next to the recipe during the ``devtool finish``
+   command.
+
+   If you specify a destination layer that is the same as the original
+   source, then the old version of the recipe and associated files are
+   removed prior to adding the new version. $ devtool finish recipe
+   layer
+
+   .. note::
+
+      Any changes you want to turn into patches must be committed to the
+      Git repository in the source tree.
+
+   As a final process of the ``devtool finish`` command, the state of
+   the standard layers and the upstream source is restored so that you
+   can build the recipe from those areas rather than the workspace.
+
+   .. note::
+
+      You can use the
+      devtool reset
+      command to put things back should you decide you do not want to
+      proceed with your work. If you do use this command, realize that
+      the source tree is preserved.
+
+.. _sdk-a-closer-look-at-devtool-add:
+
+A Closer Look at ``devtool add``
+================================
+
+The ``devtool add`` command automatically creates a recipe based on the
+source tree you provide with the command. Currently, the command has
+support for the following:
+
+-  Autotools (``autoconf`` and ``automake``)
+
+-  CMake
+
+-  Scons
+
+-  ``qmake``
+
+-  Plain ``Makefile``
+
+-  Out-of-tree kernel module
+
+-  Binary package (i.e. "-b" option)
+
+-  Node.js module
+
+-  Python modules that use ``setuptools`` or ``distutils``
+
+Apart from binary packages, the determination of how a source tree
+should be treated is automatic based on the files present within that
+source tree. For example, if a ``CMakeLists.txt`` file is found, then
+the source tree is assumed to be using CMake and is treated accordingly.
+
+.. note::
+
+   In most cases, you need to edit the automatically generated recipe in
+   order to make it build properly. Typically, you would go through
+   several edit and build cycles until the recipe successfully builds.
+   Once the recipe builds, you could use possible further iterations to
+   test the recipe on the target device.
+
+The remainder of this section covers specifics regarding how parts of
+the recipe are generated.
+
+.. _sdk-name-and-version:
+
+Name and Version
+----------------
+
+If you do not specify a name and version on the command line,
+``devtool add`` uses various metadata within the source tree in an
+attempt to determine the name and version of the software being built.
+Based on what the tool determines, ``devtool`` sets the name of the
+created recipe file accordingly.
+
+If ``devtool`` cannot determine the name and version, the command prints
+an error. For such cases, you must re-run the command and provide the
+name and version, just the name, or just the version as part of the
+command line.
+
+Sometimes the name or version determined from the source tree might be
+incorrect. For such a case, you must reset the recipe: $ devtool reset
+-n recipename After running the ``devtool reset`` command, you need to
+run ``devtool add`` again and provide the name or the version.
+
+.. _sdk-dependency-detection-and-mapping:
+
+Dependency Detection and Mapping
+--------------------------------
+
+The ``devtool add`` command attempts to detect build-time dependencies
+and map them to other recipes in the system. During this mapping, the
+command fills in the names of those recipes as part of the
+```DEPENDS`` <&YOCTO_DOCS_REF_URL;#var-DEPENDS>`__ variable within the
+recipe. If a dependency cannot be mapped, ``devtool`` places a comment
+in the recipe indicating such. The inability to map a dependency can
+result from naming not being recognized or because the dependency simply
+is not available. For cases where the dependency is not available, you
+must use the ``devtool add`` command to add an additional recipe that
+satisfies the dependency. Once you add that recipe, you need to update
+the ``DEPENDS`` variable in the original recipe to include the new
+recipe.
+
+If you need to add runtime dependencies, you can do so by adding the
+following to your recipe: RDEPENDS_${PN} += "dependency1 dependency2
+..."
+
+.. note::
+
+   The
+   devtool add
+   command often cannot distinguish between mandatory and optional
+   dependencies. Consequently, some of the detected dependencies might
+   in fact be optional. When in doubt, consult the documentation or the
+   configure script for the software the recipe is building for further
+   details. In some cases, you might find you can substitute the
+   dependency with an option that disables the associated functionality
+   passed to the configure script.
+
+.. _sdk-license-detection:
+
+License Detection
+-----------------
+
+The ``devtool add`` command attempts to determine if the software you
+are adding is able to be distributed under a common, open-source
+license. If so, the command sets the
+```LICENSE`` <&YOCTO_DOCS_REF_URL;#var-LICENSE>`__ value accordingly.
+You should double-check the value added by the command against the
+documentation or source files for the software you are building and, if
+necessary, update that ``LICENSE`` value.
+
+The ``devtool add`` command also sets the
+```LIC_FILES_CHKSUM`` <&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM>`__
+value to point to all files that appear to be license-related. Realize
+that license statements often appear in comments at the top of source
+files or within the documentation. In such cases, the command does not
+recognize those license statements. Consequently, you might need to
+amend the ``LIC_FILES_CHKSUM`` variable to point to one or more of those
+comments if present. Setting ``LIC_FILES_CHKSUM`` is particularly
+important for third-party software. The mechanism attempts to ensure
+correct licensing should you upgrade the recipe to a newer upstream
+version in future. Any change in licensing is detected and you receive
+an error prompting you to check the license text again.
+
+If the ``devtool add`` command cannot determine licensing information,
+``devtool`` sets the ``LICENSE`` value to "CLOSED" and leaves the
+``LIC_FILES_CHKSUM`` value unset. This behavior allows you to continue
+with development even though the settings are unlikely to be correct in
+all cases. You should check the documentation or source files for the
+software you are building to determine the actual license.
+
+.. _sdk-adding-makefile-only-software:
+
+Adding Makefile-Only Software
+-----------------------------
+
+The use of Make by itself is very common in both proprietary and
+open-source software. Unfortunately, Makefiles are often not written
+with cross-compilation in mind. Thus, ``devtool add`` often cannot do
+very much to ensure that these Makefiles build correctly. It is very
+common, for example, to explicitly call ``gcc`` instead of using the
+```CC`` <&YOCTO_DOCS_REF_URL;#var-CC>`__ variable. Usually, in a
+cross-compilation environment, ``gcc`` is the compiler for the build
+host and the cross-compiler is named something similar to
+``arm-poky-linux-gnueabi-gcc`` and might require arguments (e.g. to
+point to the associated sysroot for the target machine).
+
+When writing a recipe for Makefile-only software, keep the following in
+mind:
+
+-  You probably need to patch the Makefile to use variables instead of
+   hardcoding tools within the toolchain such as ``gcc`` and ``g++``.
+
+-  The environment in which Make runs is set up with various standard
+   variables for compilation (e.g. ``CC``, ``CXX``, and so forth) in a
+   similar manner to the environment set up by the SDK's environment
+   setup script. One easy way to see these variables is to run the
+   ``devtool build`` command on the recipe and then look in
+   ``oe-logs/run.do_compile``. Towards the top of this file, a list of
+   environment variables exists that are being set. You can take
+   advantage of these variables within the Makefile.
+
+-  If the Makefile sets a default for a variable using "=", that default
+   overrides the value set in the environment, which is usually not
+   desirable. For this case, you can either patch the Makefile so it
+   sets the default using the "?=" operator, or you can alternatively
+   force the value on the ``make`` command line. To force the value on
+   the command line, add the variable setting to
+   ```EXTRA_OEMAKE`` <&YOCTO_DOCS_REF_URL;#var-EXTRA_OEMAKE>`__ or
+   ```PACKAGECONFIG_CONFARGS`` <&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG_CONFARGS>`__
+   within the recipe. Here is an example using ``EXTRA_OEMAKE``:
+   EXTRA_OEMAKE += "'CC=${CC}' 'CXX=${CXX}'" In the above example,
+   single quotes are used around the variable settings as the values are
+   likely to contain spaces because required default options are passed
+   to the compiler.
+
+-  Hardcoding paths inside Makefiles is often problematic in a
+   cross-compilation environment. This is particularly true because
+   those hardcoded paths often point to locations on the build host and
+   thus will either be read-only or will introduce contamination into
+   the cross-compilation because they are specific to the build host
+   rather than the target. Patching the Makefile to use prefix variables
+   or other path variables is usually the way to handle this situation.
+
+-  Sometimes a Makefile runs target-specific commands such as
+   ``ldconfig``. For such cases, you might be able to apply patches that
+   remove these commands from the Makefile.
+
+.. _sdk-adding-native-tools:
+
+Adding Native Tools
+-------------------
+
+Often, you need to build additional tools that run on the `build
+host <&YOCTO_DOCS_REF_URL;#hardware-build-system-term>`__ as opposed to
+the target. You should indicate this requirement by using one of the
+following methods when you run ``devtool add``:
+
+-  Specify the name of the recipe such that it ends with "-native".
+   Specifying the name like this produces a recipe that only builds for
+   the build host.
+
+-  Specify the "DASHDASHalso-native" option with the ``devtool add``
+   command. Specifying this option creates a recipe file that still
+   builds for the target but also creates a variant with a "-native"
+   suffix that builds for the build host.
+
+.. note::
+
+   If you need to add a tool that is shipped as part of a source tree
+   that builds code for the target, you can typically accomplish this by
+   building the native and target parts separately rather than within
+   the same compilation process. Realize though that with the
+   "DASHDASHalso-native" option, you can add the tool using just one
+   recipe file.
+
+.. _sdk-adding-node-js-modules:
+
+Adding Node.js Modules
+----------------------
+
+You can use the ``devtool add`` command two different ways to add
+Node.js modules: 1) Through ``npm`` and, 2) from a repository or local
+source.
+
+Use the following form to add Node.js modules through ``npm``: $ devtool
+add "npm://registry.npmjs.org;name=forever;version=0.15.1" The name and
+version parameters are mandatory. Lockdown and shrinkwrap files are
+generated and pointed to by the recipe in order to freeze the version
+that is fetched for the dependencies according to the first time. This
+also saves checksums that are verified on future fetches. Together,
+these behaviors ensure the reproducibility and integrity of the build.
+
+.. note::
+
+   -  You must use quotes around the URL. The ``devtool add`` does not
+      require the quotes, but the shell considers ";" as a splitter
+      between multiple commands. Thus, without the quotes,
+      ``devtool add`` does not receive the other parts, which results in
+      several "command not found" errors.
+
+   -  In order to support adding Node.js modules, a ``nodejs`` recipe
+      must be part of your SDK.
+
+As mentioned earlier, you can also add Node.js modules directly from a
+repository or local source tree. To add modules this way, use
+``devtool add`` in the following form: $ devtool add
+https://github.com/diversario/node-ssdp In this example, ``devtool``
+fetches the specified Git repository, detects the code as Node.js code,
+fetches dependencies using ``npm``, and sets
+```SRC_URI`` <&YOCTO_DOCS_REF_URL;#var-SRC_URI>`__ accordingly.
+
+.. _sdk-working-with-recipes:
+
+Working With Recipes
+====================
+
+When building a recipe using the ``devtool build`` command, the typical
+build progresses as follows:
+
+1. Fetch the source
+
+2. Unpack the source
+
+3. Configure the source
+
+4. Compile the source
+
+5. Install the build output
+
+6. Package the installed output
+
+For recipes in the workspace, fetching and unpacking is disabled as the
+source tree has already been prepared and is persistent. Each of these
+build steps is defined as a function (task), usually with a "do_" prefix
+(e.g. ```do_fetch`` <&YOCTO_DOCS_REF_URL;#ref-tasks-fetch>`__,
+```do_unpack`` <&YOCTO_DOCS_REF_URL;#ref-tasks-unpack>`__, and so
+forth). These functions are typically shell scripts but can instead be
+written in Python.
+
+If you look at the contents of a recipe, you will see that the recipe
+does not include complete instructions for building the software.
+Instead, common functionality is encapsulated in classes inherited with
+the ``inherit`` directive. This technique leaves the recipe to describe
+just the things that are specific to the software being built. A
+```base`` <&YOCTO_DOCS_REF_URL;#ref-classes-base>`__ class exists that
+is implicitly inherited by all recipes and provides the functionality
+that most recipes typically need.
+
+The remainder of this section presents information useful when working
+with recipes.
+
+.. _sdk-finding-logs-and-work-files:
+
+Finding Logs and Work Files
+---------------------------
+
+After the first run of the ``devtool build`` command, recipes that were
+previously created using the ``devtool add`` command or whose sources
+were modified using the ``devtool modify`` command contain symbolic
+links created within the source tree:
+
+-  ``oe-logs``: This link points to the directory in which log files and
+   run scripts for each build step are created.
+
+-  ``oe-workdir``: This link points to the temporary work area for the
+   recipe. The following locations under ``oe-workdir`` are particularly
+   useful:
+
+   -  ``image/``: Contains all of the files installed during the
+      ```do_install`` <&YOCTO_DOCS_REF_URL;#ref-tasks-install>`__ stage.
+      Within a recipe, this directory is referred to by the expression
+      ``${``\ ```D`` <&YOCTO_DOCS_REF_URL;#var-D>`__\ ``}``.
+
+   -  ``sysroot-destdir/``: Contains a subset of files installed within
+      ``do_install`` that have been put into the shared sysroot. For
+      more information, see the "`Sharing Files Between
+      Recipes <#sdk-sharing-files-between-recipes>`__" section.
+
+   -  ``packages-split/``: Contains subdirectories for each package
+      produced by the recipe. For more information, see the
+      "`Packaging <#sdk-packaging>`__" section.
+
+You can use these links to get more information on what is happening at
+each build step.
+
+.. _sdk-setting-configure-arguments:
+
+Setting Configure Arguments
+---------------------------
+
+If the software your recipe is building uses GNU autoconf, then a fixed
+set of arguments is passed to it to enable cross-compilation plus any
+extras specified by
+```EXTRA_OECONF`` <&YOCTO_DOCS_REF_URL;#var-EXTRA_OECONF>`__ or
+```PACKAGECONFIG_CONFARGS`` <&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG_CONFARGS>`__
+set within the recipe. If you wish to pass additional options, add them
+to ``EXTRA_OECONF`` or ``PACKAGECONFIG_CONFARGS``. Other supported build
+tools have similar variables (e.g.
+```EXTRA_OECMAKE`` <&YOCTO_DOCS_REF_URL;#var-EXTRA_OECMAKE>`__ for
+CMake, ```EXTRA_OESCONS`` <&YOCTO_DOCS_REF_URL;#var-EXTRA_OESCONS>`__
+for Scons, and so forth). If you need to pass anything on the ``make``
+command line, you can use ``EXTRA_OEMAKE`` or the
+```PACKAGECONFIG_CONFARGS`` <&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG_CONFARGS>`__
+variables to do so.
+
+You can use the ``devtool configure-help`` command to help you set the
+arguments listed in the previous paragraph. The command determines the
+exact options being passed, and shows them to you along with any custom
+arguments specified through ``EXTRA_OECONF`` or
+``PACKAGECONFIG_CONFARGS``. If applicable, the command also shows you
+the output of the configure script's "DASHDASHhelp" option as a
+reference.
+
+.. _sdk-sharing-files-between-recipes:
+
+Sharing Files Between Recipes
+-----------------------------
+
+Recipes often need to use files provided by other recipes on the `build
+host <&YOCTO_DOCS_REF_URL;#hardware-build-system-term>`__. For example,
+an application linking to a common library needs access to the library
+itself and its associated headers. The way this access is accomplished
+within the extensible SDK is through the sysroot. One sysroot exists per
+"machine" for which the SDK is being built. In practical terms, this
+means a sysroot exists for the target machine, and a sysroot exists for
+the build host.
+
+Recipes should never write files directly into the sysroot. Instead,
+files should be installed into standard locations during the
+```do_install`` <&YOCTO_DOCS_REF_URL;#ref-tasks-install>`__ task within
+the ``${``\ ```D`` <&YOCTO_DOCS_REF_URL;#var-D>`__\ ``}`` directory. A
+subset of these files automatically goes into the sysroot. The reason
+for this limitation is that almost all files that go into the sysroot
+are cataloged in manifests in order to ensure they can be removed later
+when a recipe is modified or removed. Thus, the sysroot is able to
+remain free from stale files.
+
+.. _sdk-packaging:
+
+Packaging
+---------
+
+Packaging is not always particularly relevant within the extensible SDK.
+However, if you examine how build output gets into the final image on
+the target device, it is important to understand packaging because the
+contents of the image are expressed in terms of packages and not
+recipes.
+
+During the ```do_package`` <&YOCTO_DOCS_REF_URL;#ref-tasks-package>`__
+task, files installed during the
+```do_install`` <&YOCTO_DOCS_REF_URL;#ref-tasks-install>`__ task are
+split into one main package, which is almost always named the same as
+the recipe, and into several other packages. This separation exists
+because not all of those installed files are useful in every image. For
+example, you probably do not need any of the documentation installed in
+a production image. Consequently, for each recipe the documentation
+files are separated into a ``-doc`` package. Recipes that package
+software containing optional modules or plugins might undergo additional
+package splitting as well.
+
+After building a recipe, you can see where files have gone by looking in
+the ``oe-workdir/packages-split`` directory, which contains a
+subdirectory for each package. Apart from some advanced cases, the
+```PACKAGES`` <&YOCTO_DOCS_REF_URL;#var-PACKAGES>`__ and
+```FILES`` <&YOCTO_DOCS_REF_URL;#var-FILES>`__ variables controls
+splitting. The ``PACKAGES`` variable lists all of the packages to be
+produced, while the ``FILES`` variable specifies which files to include
+in each package by using an override to specify the package. For
+example, ``FILES_${PN}`` specifies the files to go into the main package
+(i.e. the main package has the same name as the recipe and
+``${``\ ```PN`` <&YOCTO_DOCS_REF_URL;#var-PN>`__\ ``}`` evaluates to the
+recipe name). The order of the ``PACKAGES`` value is significant. For
+each installed file, the first package whose ``FILES`` value matches the
+file is the package into which the file goes. Defaults exist for both
+the ``PACKAGES`` and ``FILES`` variables. Consequently, you might find
+you do not even need to set these variables in your recipe unless the
+software the recipe is building installs files into non-standard
+locations.
+
+.. _sdk-restoring-the-target-device-to-its-original-state:
+
+Restoring the Target Device to its Original State
+=================================================
+
+If you use the ``devtool deploy-target`` command to write a recipe's
+build output to the target, and you are working on an existing component
+of the system, then you might find yourself in a situation where you
+need to restore the original files that existed prior to running the
+``devtool deploy-target`` command. Because the ``devtool deploy-target``
+command backs up any files it overwrites, you can use the
+``devtool undeploy-target`` command to restore those files and remove
+any other files the recipe deployed. Consider the following example: $
+devtool undeploy-target lighttpd root@192.168.7.2 If you have deployed
+multiple applications, you can remove them all using the "-a" option
+thus restoring the target device to its original state: $ devtool
+undeploy-target -a root@192.168.7.2 Information about files deployed to
+the target as well as any backed up files are stored on the target
+itself. This storage, of course, requires some additional space on the
+target machine.
+
+.. note::
+
+   The
+   devtool deploy-target
+   and
+   devtool undeploy-target
+   commands do not currently interact with any package management system
+   on the target device (e.g. RPM or OPKG). Consequently, you should not
+   intermingle
+   devtool deploy-target
+   and package manager operations on the target device. Doing so could
+   result in a conflicting set of files.
+
+.. _sdk-installing-additional-items-into-the-extensible-sdk:
+
+Installing Additional Items Into the Extensible SDK
+===================================================
+
+Out of the box the extensible SDK typically only comes with a small
+number of tools and libraries. A minimal SDK starts mostly empty and is
+populated on-demand. Sometimes you must explicitly install extra items
+into the SDK. If you need these extra items, you can first search for
+the items using the ``devtool search`` command. For example, suppose you
+need to link to libGL but you are not sure which recipe provides libGL.
+You can use the following command to find out: $ devtool search libGL
+mesa A free implementation of the OpenGL API Once you know the recipe
+(i.e. ``mesa`` in this example), you can install it: $ devtool
+sdk-install mesa By default, the ``devtool sdk-install`` command assumes
+the item is available in pre-built form from your SDK provider. If the
+item is not available and it is acceptable to build the item from
+source, you can add the "-s" option as follows: $ devtool sdk-install -s
+mesa It is important to remember that building the item from source
+takes significantly longer than installing the pre-built artifact. Also,
+if no recipe exists for the item you want to add to the SDK, you must
+instead add the item using the ``devtool add`` command.
+
+.. _sdk-applying-updates-to-an-installed-extensible-sdk:
+
+Applying Updates to an Installed Extensible SDK
+===============================================
+
+If you are working with an installed extensible SDK that gets
+occasionally updated (e.g. a third-party SDK), then you will need to
+manually "pull down" the updates into the installed SDK.
+
+To update your installed SDK, use ``devtool`` as follows: $ devtool
+sdk-update The previous command assumes your SDK provider has set the
+default update URL for you through the
+```SDK_UPDATE_URL`` <&YOCTO_DOCS_REF_URL;#var-SDK_UPDATE_URL>`__
+variable as described in the "`Providing Updates to the Extensible SDK
+After
+Installation <#sdk-providing-updates-to-the-extensible-sdk-after-installation>`__"
+section. If the SDK provider has not set that default URL, you need to
+specify it yourself in the command as follows: $ devtool sdk-update
+path_to_update_directory
+
+.. note::
+
+   The URL needs to point specifically to a published SDK and not to an
+   SDK installer that you would download and install.
+
+.. _sdk-creating-a-derivative-sdk-with-additional-components:
+
+Creating a Derivative SDK With Additional Components
+====================================================
+
+You might need to produce an SDK that contains your own custom
+libraries. A good example would be if you were a vendor with customers
+that use your SDK to build their own platform-specific software and
+those customers need an SDK that has custom libraries. In such a case,
+you can produce a derivative SDK based on the currently installed SDK
+fairly easily by following these steps:
+
+1. If necessary, install an extensible SDK that you want to use as a
+   base for your derivative SDK.
+
+2. Source the environment script for the SDK.
+
+3. Add the extra libraries or other components you want by using the
+   ``devtool add`` command.
+
+4. Run the ``devtool build-sdk`` command.
+
+The previous steps take the recipes added to the workspace and construct
+a new SDK installer that contains those recipes and the resulting binary
+artifacts. The recipes go into their own separate layer in the
+constructed derivative SDK, which leaves the workspace clean and ready
+for users to add their own recipes.