The Gentoo.org Redesign, Part 1

Ebuild Functions

Ebuilds provide the ability to define various shell functions that are used to specify various actions relating to building and installing a source or binary package on a user's system. When an ebuild is emerged, the following functions are called, in order:

• pkg_setup - variable intialization and sanity checks
• src_unpack
• src_prepare
• src_configure
• src_compile
• src_install

At this point, the files are ready to be "merged" into the live filesystem. This is when they are copied from the temporary build directory into /usr, etc. At this point, the following functions are executed:

• pkg_preinst
• (files are merged)
• pkg_postinst

src_* functions

Ebuild functions starting with src_ are all related to creating the ebuild or package from source code/artifacts, and are defined below:

src_unpack

src_unpack is intended to be used to unpack the source code/artifacts that will be used by the other src_* functions. With EAPI 1 and earlier, it is also used for patching/modifying the source artifacts to prepare them for building, but with EAPI 2 or later the src_prepare function should be used for this instead. When src_unpack starts, the current working directory is set to $WORKDIR, which is the directory within which all source code/artifacts should be expanded. Note that the variable $A is set to the names of all the unique source files/artifacts specified in SRC_URI, and they will all be available in $DISTDIR by the time src_unpack starts. Also note that if no src_unpack function is specified, ebuild.sh will execute the following function for src_unpack by default:

src_unpack() {
  unpack ${A}
}

src_prepare

EAPI 2 and above support the src_prepare function, which is intended to be used for applying patches or making other modifications to the source code. When src_prepare starts, the current working directory is set to $S.

src_configure

EAPI 2 and above support the src_configure function, which is used to configure the source code prior to compilation. With EAPI 2 and above, the following default src_configure is defined if none is specified:

src_configure() {
	if [[ -x ${ECONF_SOURCE:-.}/configure ]] ; then
		econf
	fi
}

src_compile

This function defines the steps necessary to compile source code. With EAPI 1 and earlier, this function is also used to configure the source code prior to compilation. However, starting with EAPI 2, the src_configure function must be used for configuration steps instead of bundling them inside src_compile. In addition, starting with EAPI 2, there is now a default src_compile function that will be executed if none is defined in the ebuild:

src_compile() {
	if [ -f Makefile ] || [ -f GNUmakefile ] || [ -f makefile ] ; then
		emake || die "emake failed"
	fi
}

src_test

src_test is an interesting function - by default, an end-user's Portage does not have tests enabled. But if a user has test in FEATURES, or EBUILD_FORCE_TEST is defined, then ebuild.sh will attempt to run a test suite for this ebuild, by executing make check or make test if these targets are defined in the Makefile; otherwise, no tests will execute. If your Makefile supports make check or make test but the test suite is broken, then specify RESTRICT="test" in your ebuild to disable the test suite.

src_install

src_install is used by the ebuild writer to install all to-be-installed files to the $D directory, which can be treated like an empty root filesystem, in that ${D}/usr is the equivalent of the /usr directory, etc. When src_install runs, the Portage sandbox will be enabled, which will prevent any processes from creating or modifying files outside of the ${D} filesystem tree, and a sandbox violation will occur (resulting in the termination of the ebuild) if any such sandbox violation should occur. Once src_install has perfomed all necessary steps to install all to-be-installed files to $D, Portage will take care of merging these files to the filesystem specified by the $ROOT environment variable, which defaults to / if not set. When Portage merges these files, it will also record information about the installed package to /var/db/pkg/(cat)/$P. Typically, a src_install function such as this is sufficient for ensuring that all to-be-installed files are installed to $D:

src_install() {
  make DESTDIR="$D" install
}

pkg_* functions

An ebuild's functions starting with pkg_* take a wider view of the package lifecycle, and may be executed very early or very late in the build or package installation process. They are also all executed even if installing a Portage binary package, so are the intended place for defining any global configuration changes that are also required during binary package installation, such as user and group creation. When these functions are executed, the $ROOT variable will be defined to point to the target root filesystem to which the package is to be (or has been) installed. All logic inside pkg_* functions must function properly even if $ROOT is something other than /.

pkg_setup

The pkg_setup function is unusual in that it runs prior to any src_* function, and also runs prior to any other pkg_* function that runs when a binary package is installed, so it provides a useful place for the ebuild writer to perform any sanity checks, global configuration changes to the system (such as user/group creation) or set any internal global variables that are used by the rest of the ebuild. Using this function for defining global variables that are needed in multiple other functions is a useful way of avoiding duplicate code. You should also look to pkg_setup as the ideal place to put any logic that would otherwise linger in the main body of the ebuild, which should be avoided at all costs as it will slow down dependency calculation by Portage. Also remember that Portage can build binary packages, and this function is a good place to execute any steps that are required to run both prior to building an ebuild, and prior to installing a package. Also consider using pkg_preinst and pkg_postinst for this purpose.

pkg_pretend

The pkg_pretend function was added with EAPI 3, and it's the opinion of Daniel Robbins that the use of this function should be avoided. This function is especially unusual in that it is intended to be run during dependency calculation, and is intended to provide a polite mechanism to inform the user that a particular ebuild will fail due to a known incompatibility, typically a kernel incompatibility. That way, the user can know during emerge --pretend that a merge will fail. While this is useful, extending the dependency engine using bash is a very low-performance means to perform these tests. Therefore, The Funtoo core team recommends against using pkg_pretend. An extensible dependency engine would be a more appropriate and high-performance way to provide identical functionality.

pkg_preinst

The pkg_preinst function is called by Portage, prior to merging the to-be-installed files to the target filesystem specified by $ROOT environment variable (which defaults to /.) Keep in mind that these to-be-installed files were either just compiled and installed to $D by src_install, or they were just extracted from a .tbz2 binary package. The pkg_preinst function provides an ideal place to perform any "just before install" actions, such as user and group creation or other necessary steps to ensure that the package merges successfully. It also provides a potential place to perform any sanity checks related to installing the package to the target filesystem. If any sanity checks fail, calling die from this function will cause the package to not be installed to the target filesystem.

pkg_postinst

The pkg_postinst function is called by Portage prior to the package being installed to the target filesystem specified by $ROOT. This is a good place to perform any post-install configuration actions as well as print any informational messages for the user's benefit related to the package that was just installed.

pkg_prerm

The pkg_prerm function is called by Portage before an ebuild is removed from the filesystem.

pkg_postrm

The pkg_postrm function is called by Portage after an ebuild is removed from the filesystem.

pkg_config

The pkg_config function is called by Portage when the user calls emerge --config for the ebuild. The current directory will be set to the current directory of the shell from where emerge --config is run.

Skipping over a function

To skip over a function, create a function that does not do anything. The recommended way is to use bash no-op command:

# Skip src_prepare.
src_prepare() { :; }

Extra pre_ and post_ functions

Modern versions of Portage also support functions identical to the above functions but with pre_ and post_ at the beginning of the function name. For example, post_src_configure will be executed after src_configure and before src_compile. These additional functions are supported by all EAPIs, provided that the parent function is supported by the EAPI in use. The initial current working directory should be identical to the initial current working directory of the parent function.

Helper Functions

econf()

econf() is part of ebuild.sh and is intended to be a wrapper to the configure command that is typically used in the src_configure() stage. It has a number of behaviors that are important for ebuild writers to understand. Once you understand what econf() does, you are free to use it in your ebuilds. Note that the behavior of econf() is generally safe for most autoconf-based source archives, but in some cases it may be necessary to avoid using econf() to avoid some of its default behaviors.

Automatically set prefix

--prefix=/usr will be passed to configure automatically, unless a --prefix argument was specified to econf(), in which case, that --prefix setting will be used instead.

Automatically set libdir

If the ABI variable is set (typically done in the profile), then econf() will look for a variable named LIBDIR_$ABI (ie. LIBDIR_amd64). If this variable is set, the value of this variable will be used to set libdir to the value of {prefix}/LIBDIR_$ABI.

Automatically set CHOST and CTARGET

The --host=$CHOST argument will be passed to configure. $CHOST is defined in the system profile. In addition, the --target=$CTARGET argument will be passed to configure if $CTARGET is defined. This is not normally required but is done to make Portage more capable of cross-compiling the ebuild. However, this functionality is not a guarantee that your ebuild will successfully cross-compile, as other changes to the ebuild may be necessary.

Disable Dependency Tracking (EAPI 4)

In EAPI 4, the --disable-dependency-tracking argument will be passed to configure in order to optimize the performance of the configuration process. This option should have no impact other than on the performance of the configure script.

List of arguments

The following arguments are passed to configure and are all overrideable by the user by passing similar options to econf():

• --prefix=/usr
• --libdir={prefix}/LIBDIR_$ABI
• --host=${CHOST}
• if CTARGET is defined, then --target=${CTARGET}
• --mandir=/usr/share/man
• --infodir=/usr/share/info
• --datadir=/usr/share
• --sysconfdir=/etc
• --localstatedir=/var/lib
• if EAPI 4+, then --disable-dependency-tracking