upstream_commit = $$(printf '%s\n' '$(OPK_SOURCE_VERSION_UPSTREAM)' | \
	sed 's/^.*[~+]git........\.\([0-9a-f]*\).*$$/\1/')
upstream_git_uri = git://linuxtv.org/$(OPK_SOURCE).git
source_archive = ../$(OPK_SOURCE)-$(OPK_SOURCE_VERSION_UPSTREAM).orig.tar.bz2

$(source_archive):
	git clone $(upstream_git_uri) $(OPK_SOURCE)/
	(cd $(OPK_SOURCE)/ && git archive --format=tar --prefix=$(OPK_SOURCE)/ \
		"$(upstream_commit)") | bzip2 >$@

source: $(source_archive)