[PATCH] sbuild: Fix low hit ratio for ccache on linux kernel rebuild

[Uladzimir Bely <ubely@ilbers.de>]

For some targets defconfig for linux recipe includes option
CONFIG_DEBUG_INFO that embeds absolute path to the source files
into compiled binaries.

While sbuild uses unique directory to place sources for each build
by default, it happens that ccache hits ration is to small on rebuild.

This patch makes sbuild use the same build directory for sequential
builds. While several packages can be built in parallel (e.g. same
package for different architectures), WORKDIR is used to generate
hash part for the build directory of sbuild.

Signed-off-by: Uladzimir Bely <ubely@ilbers.de>
---
 meta/classes/dpkg.bbclass | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/meta/classes/dpkg.bbclass b/meta/classes/dpkg.bbclass
index b726ea9d..016e46c4 100644
--- a/meta/classes/dpkg.bbclass
+++ b/meta/classes/dpkg.bbclass
@@ -82,6 +82,8 @@ dpkg_runbuild() {
     sh -c "cd ${WORKDIR}; dpkg-source -q -b ${PPS}"
     DSC_FILE=$(find ${WORKDIR} -name "${DEB_SOURCE_NAME}*.dsc" -print)
 
+    build_path_hash=$(echo "${WORKDIR}" | md5sum | cut -b1-6)
+
     sbuild -A -n -c ${SBUILD_CHROOT} --extra-repository="${ISAR_APT_REPO}" \
         --host=${PACKAGE_ARCH} --build=${SBUILD_HOST_ARCH} ${profiles} \
         --no-run-lintian --no-run-piuparts --no-run-autopkgtest --resolve-alternatives \
@@ -91,6 +93,7 @@ dpkg_runbuild() {
         --finished-build-commands="cp -n --no-preserve=owner ${deb_dir}/*.deb -t ${ext_deb_dir}/ || :" \
         --finished-build-commands="cp /var/log/dpkg.log ${ext_root}/dpkg_partial.log" \
         --debbuildopts="--source-option=-I" \
+        --build-path="/build/${PN}-${build_path_hash}" \
         --build-dir=${WORKDIR} --dist="isar" ${DSC_FILE}
 
     sbuild_dpkg_log_export "${WORKDIR}/rootfs/dpkg_partial.log"
-- 
2.20.1