Migrating metadata to OE-Core

The classes and BitBake configuration used in OpenEmbedded-Core require a few changes for recipes brought over from OE-Classic (and for new recipes written by developers used to working with OE-Classic).

Mandatory changes

For recipes the following changes are required in order to build successfully:

• Add LIC_FILES_CHKSUM: this specifies one or more files or sections of files from the source that can be used to detect if the license of the software has been changed in a newer version. It is mandatory and checked at the end of do_configure. See Specifying LIC_FILES_CHKSUM for more details.
• Remove legacy staging: legacy staging (do_stage) is no longer supported and BitBake will error out on parse of recipes that use it. Items previously in do_stage should be moved to do_install as appropriate; however they should actually install the files to somewhere under ${D} and not copy them into the staging directory directly or things will break later on. See Legacy staging for more information.
• Ensure LICENSE is present: the LICENSE field, whilst usually included in most recipes in the past anyway, is now mandatory. It should be as specific and as correct as possible (e.g. "GPLv2", not just "GPL") and try to be consistent with other recipes.
• Ensure SRC_URI checksums are present: for entries in SRC_URI pointing to sources other than SCMs or local files, i.e. http, ftp, etc., at least one SRC_URI checksum (md5sum/sha256sum) must be provided. If these are not present for an entry where it is required you will get an error which gives you the appropriate values to be added to the recipe. You can use the "name=" parameter within SRC_URI to distinguish between multiple entries. (This used to be optional, now it is mandatory.)
• Remove comments in string values: recent versions of BitBake no longer allow comments in multi-line strings, so the tradition of being able to comment out lines within a multi-line SRC_URI or when setting configure flags etc. is no longer allowed. Remove the commented out lines or move them to beyond where the string terminates.
• Ensure values are quoted: current versions of BitBake require that values are quoted; this was optional in the past. Single or double quotes are allowed but all values must now be quoted. (This does not affect how numeric values are interpreted, these have always been treated as strings.)
• Use package name override with packaging variables: the runtime package specific variables (RDEPENDS, RRECOMMENDS, RSUGGESTS, RPROVIDES, RCONFLICTS, RREPLACES, FILES, ALLOW_EMPTY, and the pre/post install/uninstall script functions pkg_preinst, pkg_postinst, pkg_prerm, and pkg_postrm) should always have a package name override. For example, to set a runtime dependency for the main package use RDEPENDS_${PN}.
• Replace oe* logging commands: Any calls to oenote, oewarn, oefatal etc. in shell scripts need to be replaced with the "bb" equivalent, i.e. bbnote, bbwarn, bbfatal etc.
• Use FILESEXTRAPATHS to extend file search path: Modifications to FILESPATHPKG and/or FILESPATH (or FILESDIR which is deprecated) should be replaced by prepending to FILESEXTRAPATHS; in addition, you no longer need to define THISDIR (and should not do so). For example, to add a directory to be searched for patches and other files which is named with PN, do the following (note the immediate evaluation operator := and trailing colon, these are important):

FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

Changes applicable to the "danny" release and later:

• Python functions should always use four spaces for indentation and not tabs - a warning will be produced if tabs are found. Previously four spaces was the convention but many python functions used tabs. This has been fixed in OE-Core and other layers, and since python uses indentation for statement blocks, is very important that you make the same changes to python functions in your recipes.
• Change proto= to protocol= in SRC_URI - all fetchers have been changed to be consistent. Previously, some fetchers used proto and some protocol.
• Change tasks to package groups - for custom task recipes, rename them from task-*.bb to packagegroup-*.bb, inherit packagegroup instead of inheriting task and remove anything that is now handled by meta/classes/packagegroup.bbclass. Also change any references to task-* to packagegroup-*.
• Change any assumptions that libexecdir is /usr/libexec: we now set libexecdir to ${libdir}/${BPN} to match with the Filesystem Hierarchy Standard (FHS).

Changes applicable to current master:

• Fix continuation on last line of a comment: if a comment ends in a line continuation (\) then the next line must also be a comment; any instance where this is not the case will now trigger a warning. Either remove the continuation character or make the next line a comment as well.

Best practices

The following practices are required for patch submission to layers such as OE-Core and meta-oe, and recommended for recipes in your own layers:

• Machine and distro-specific overrides should be removed from recipes for generic layers (especially meta-oe and OE-Core). These can be moved to bbappends in the appropriate machine / distro layer respectively. (Note however that architecture-specific overrides are allowed if necessary.)
• Fix any QA issues reported during packaging.
• Avoid hardcoding system paths such as /etc, /usr/bin, /usr/share and so on. Instead the values of the appropriate variables should be used (e.g. ${libdir}, ${bindir}, ${datadir} ...). If there are scripts or other files provided by the application such as initscripts you can fix the paths in them within do_install using sed. See bitbake.conf for a list of standard path variables and their default values (which may be - and often are - overridden by the distro configuration).
• Initscripts should have the standard LSB header (especially if no systemd unit file is being provided, since systemd relies upon information in the header when handling an initscript.)
• In-tree patches to be applied to the source should have a proper header explaining what the patch does, a valid Signed-off-by, an Upstream-Status indicator.
• Initially reset PR to "r0" (or remove it which amounts to the same thing). PR is definitely still used, but we can start again from r0.
• Use ${BPN} instead of ${PN} where you just want the recipe name without any prefixes/suffixes added by things like multilib and nativesdk (e.g. installation paths)
• NATIVE_INSTALL_WORKS for native recipes is no longer used and should be removed.
• PRIORITY is no longer used and should be removed.
• Use d.getVar/d.setVar instead of bb.data.getVar/bb.data.setVar in python functions. The latter will still work, but are deprecated.
• "Bashisms" in shell scripts (particularly those that will be executed on the host) should be avoided. This allows compatibility with alternative shells e.g. Ubuntu's default (dash).
• For readability, the variables/functions within a recipe should be ordered in the same order in which they are used - i.e. "meta" information above (DESCRIPTION, SUMMARY, DEPENDS, LICENSE etc.), followed by information needed for do_fetch (SRC_URI, etc.), then anything for do_patch, do_compile, do_install, and then do_package (e.g. PACKAGES, FILES, RDEPENDS, RRECOMMENDS...).