poky/README.structure

                 A walk through the poky directory tree
                 ======================================

Poky consists of several components and understanding what these are and where 
they each live is one of the keys to using it.

Top level core components
=========================


bitbake/

A copy of bitbake is included within poky for ease of use and resides here. 
This should usually be the same as a standard bitbake release from the bitbake 
project. Bitbake is a metadata interpreter and is responsible for reading the 
poky metadata and running the tasks it defines. Failures are usually from the
metadata and not bitbake itself and most users don't need to worry about 
bitbake. bitbake/bin is placed into the PATH environmental variable so bitbake 
can be found.

build/

This directory contains user configuration files and the output from Poky is 
also placed here.

meta/

The core metadata - this is the key part of poky. Within this directory there 
are definitions of the machines, the poky distribution and the packages that 
make up a given system.

meta-extras/

Similar to meta containing some extra package files not included in standard 
poky, disabled by default and hence not supported as part of poky.

scripts/

Various integration scripts which implement extra functionality in the poky 
environment for example the qemu scripts. This directory is appended to the 
PATH environmental variable.

sources/

Whilst not part of a checkout, poky will create this directory as part of any 
build. Any downloads are placed in this directory (as specified by the
DL_DIR variable). This directory can be shared between poky builds to save 
downloading files multiple times. SCM checkouts are also stored here as e.g.
sources/svn/, sources/cvs/ or sources/git/ and the sources directory may contain 
archives of checkouts for various revisions or dates.

Its worth noting that bitbake creates .md5 stamp files for downloads. It uses 
these to mark downloads as complete as well as for checksum and access 
accounting purposes. If you add a file manually to the directory, you need to
touch the corresponding .md5 file too.

poky-init-build-env

This script is used to setup the poky build environment. Sourcing this file in
a shell makes changes to PATH and sets other core bitbake variables based on the
current working directory. You need to use this before running poky commands.
Internally it uses scripts within the scripts/ directory to do the bulk of the 
work.


The Build Directory
===================

conf/local.conf

This file contains all the local user configuration of poky. If it isn't 
present, its created from local.conf.sample. That file contains documentation
on the various standard options which can be configured there although any 
standard conf file variable can be also be set here and usually overrides any
variable set elsewhere within poky.

Edit this file to set the MACHINE you want to build for, which package types you
which to use (PACKAGE_CLASSES) or where downloaded files should go (DL_DIR) for 
exmaple.

tmp/

This is created by bitbake if it doesn't exist and is where all the poky output
is placed. To clean poky and start a build from scratch (other than downloads), 
you can wipe this directory. tmp has some important subcomponents detailed 
below.

tmp/cache/

When bitbake parses the metadata it creates a cache file of the result which can
be used when subsequently running the command. These are stored here, usually on 
a per machine basis.

tmp/cross/

The cross compiler when generated is placed into this directory and those
beneath it.

tmp/deploy/

Any 'end result' output from poky is placed under here.

tmp/deploy/deb/

Any .deb packages emitted by poky are placed here, sorted into feeds for 
different architecture types.

tmp/deploy/images/

Complete filesystem images are placed here. If you want to flash the resulting 
image from a build onto a device, look here for them.

tmp/deploy/ipk/

Any resulting .ipk packages emitted by poky are placed here.

tmp/rootfs/

This is a temporary scratch area used when creating filesystem images. It is run
under fakeroot and is not useful once that fakeroot session has ended as 
information is lost. It is left around since it is still useful in debugging 
image creation problems.

tmp/staging/

Any package needing to share output with other packages does so within staging.
This means it contains any shared header files and any shared libraries amongst
other data. It is subdivided by architecture so multiple builds can run within
the one build directory.

tmp/stamps/

This is used by bitbake for accounting purposes to keep track of which tasks 
have been run and when. It is also subdivided by architecture. The files are 
empty and the important information is the filenames and timestamps.

tmp/work/

Each package build by bitbake is worked on its own work directory. Here, the 
source is unpacked, patched, configured, compiled etc. It is subdivided by 
architecture.

It is worth considering the structure of a typical work directory. An example is
the linux-rp kernel, version 2.6.20 r7 on the machine spitz built within poky
which would result in a work directory of 
"tmp/work/spitz-poky-linux-gnueabi/linux-rp-2.6.20-r7", referred to as WORKDIR.

Within this, the source is unpacked to linux-2.6.20 and then patched by quilt
hence the existence of the standard quilt directories linux-2.6.20/patches and 
linux-2.6.20/.pc. Within the linux-2.6.20 directory, standard quilt commands 
can be used.

There are other directories generated within WORKDIR. The most important/useful 
is WORKDIR/temp which has log files for each task (log.do_*.pid) and the scripts
bitbake runs for each task (run.do_*.pid). WORKDIR/image is where "make install"
places its output which is then split into subpackages within WORKDIR/install.


The Metadata
============

As mentioned previously, this is the core of poky. It has several important 
subdivisions:

meta/classes/

Contains the *.bbclass files. Class files are used to abstract common code 
allowing it to be reused by multiple packages. The base.bbclass file is 
inherited by every package. Examples of other important classes are 
autotools.bbclass which in theory allows any "autotooled" package to work with 
poky with minimal effort or kernel.bbclass which contains common code and 
functions for working with the linux kernel. Functions like image generation or 
packaging also have their specific class files (image.bbclass, rootfs_*.bbclass 
and package*.bbclass).

meta/conf/

This is the core set of configuration files which start from bitbake.conf and 
from which all other configuration files are included (see the includes at the 
end of the file, even local.conf is loaded from there!). Whilst bitbake.conf 
sets up the defaults, often these can be overridden by user (local.conf),
machine or distribution configuration files.

meta/conf/machine/

Contains all the machine configuration files. If you set MACHINE="spitz", the 
end result is poky looking for a spitz.conf file in this directory. The includes
directory contains various data common to multiple machines. If you want to add
support for a new machine to poky, this is the directory to look in.

meta/conf/distro/

Any distribution specific configuration is controlled from here. OpenEmbedded 
supports multiple distributions of which poky is one. Poky only contains the 
poky distribution so poky.conf is the main file here.  This includes the 
versions and SRCDATES for applications which are configured here. An example of 
an alternative configuration is poky-bleeding.conf although this mainly inherits
its configuration from poky itself.

packages/

Each application (package) poky can build has an associated .bb file which are 
all stored under this directory. Poky finds them through the BBFILES variable 
which defaults to packages/*/*.bb. Adding a new piece of software to poky 
consists of adding the appropriate .bb file. The .bb files from OpenEmbedded
upstream are usually compatible although they are not supported.

site/

Certain autoconf test results cannot be determined when cross compiling since it 
can't run tests on a live system. This directory therefore contains a list of 
cached results for various architectures which is passed to autoconf. 

                                         Copyright (C) 2006-2007 OpenedHand Ltd.