Patching with eapply

The canonical way of applying patches in ebuilds is to use the package manager's eapply command, either by calling it explicitly, or by assigning the PATCHES variable supported by the default src_prepare implementation.

Important: Applying patches to the sources from the upstream tarball is strongly preferred to distributing your own modified tarball.

The eapply command takes one or more regular file or directory paths as its arguments. Optionally, these can be preceded by GNU patch options.

Note: The -- delimiter indicates the end of options. This is useful if a filename begins with a hyphen.

If an argument is a regular file, it will be applied in the working directory by calling GNU patch with patch level -p1. Specifying an explicit -pN option will override the default patch level.
For a directory, eapply applies all patch files with names ending in .diff or .patch in that directory, in POSIXbetical order of their names. Any other files in the directory are ignored. Again, -pN can be used to override the default -p1 patch level. Note that eapply will not recurse into subdirectories.

eapply was added in EAPI 6. It differs from the previously available epatch in several ways:

eapply will not unpack patches for you.
The patch level is no longer detected automatically. Patch levels other than -p1 must be specified manually.
When specifying a directory, at least one file with a name ending in .diff or .patch must exist or the command fails.

Basic `eapply`

In its simplest form, eapply takes a single filename and applies that patch. It will automatically die if the apply fails. The following is taken from sys-libs/gpm:

	eapply "${FILESDIR}"/${P}-musl.patch

In the following simplified example taken from www-client/firefox, a patchset is added to SRC_URI in order to fetch and unpack it. eapply is then called with a directory argument. It applies all patches found in that directory:

SRC_URI+="https://dev.gentoo.org/~larry/patchsets/${P}-patches-01.tar.xz"

src_prepare() {
	eapply "${WORKDIR}/firefox-patches"
	eapply_user
}

The Patches chapter gives some guidelines about where patches should be hosted and about their formatting.

The default src_prepare function will look for a global PATCHES array to apply a list of patches for you.

PATCHES=(
	# Fix install location
	"${FILESDIR}/${P}-destdir.patch"
	# Respect MAKEOPTS #876543
	"${FILESDIR}/${P}-parallel_build.patch"
)

Advanced `eapply`

This example shows how different patch levels can be applied:

src_prepare() {
	eapply -p2 "${WORKDIR}/${P}-suse-update.patch"
	eapply -p0 "${FILESDIR}/${PV}-no-TIOCGDEV.patch"
	eapply "${FILESDIR}/${PV}-gcc-6.patch"
	eapply_user
}

Patching with eapply

Basic eapply

Advanced eapply

Basic `eapply`

Advanced `eapply`