[PATCH] linux-module: Improve KDIR retrieval

[Jan Kiszka <jan.kiszka@siemens.com>]

There might be multiple kernels installed in the buildchroot. Ensure
that we pick the one that is currently selected for the target.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 meta/recipes-kernel/linux-module/files/debian/rules |  2 --
 meta/recipes-kernel/linux-module/module.inc         | 14 ++++++++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/meta/recipes-kernel/linux-module/files/debian/rules b/meta/recipes-kernel/linux-module/files/debian/rules
index 49788da..5c1d8be 100755
--- a/meta/recipes-kernel/linux-module/files/debian/rules
+++ b/meta/recipes-kernel/linux-module/files/debian/rules
@@ -7,8 +7,6 @@
 #
 # SPDX-License-Identifier: MIT
 
-export KDIR=$(shell ls -d /lib/modules/*/build)
-
 export DEB_BUILD_OPTIONS=parallel=$(shell nproc)
 
 export CROSS_COMPILE=$(DEB_HOST_GNU_TYPE)-
diff --git a/meta/recipes-kernel/linux-module/module.inc b/meta/recipes-kernel/linux-module/module.inc
index 509dd96..5d85200 100644
--- a/meta/recipes-kernel/linux-module/module.inc
+++ b/meta/recipes-kernel/linux-module/module.inc
@@ -30,3 +30,17 @@ do_prepare_build() {
         echo "echo $module >> /etc/modules" >> ${S}/debian/postinst
     done
 }
+
+dpkg_runbuild_prepend() {
+    # Custom kernels contain the build folder directly.
+    export KDIR=$(dpkg -L --root=${BUILDCHROOT_DIR} linux-headers-${KERNEL_NAME} | \
+                  grep "/lib/modules/.*/build")
+    if [ -z "$KDIR" ]; then
+        # Debian kernels install that folder indirectly via a dependency.
+        KERNEL_DEP=$(dpkg -s --root=${BUILDCHROOT_DIR} linux-headers-${KERNEL_NAME} | \
+                     grep "^Depends: .*linux-headers-" | \
+                     sed 's/.*\(linux-headers-[^,]*\).*/\1/')
+        export KDIR=$(dpkg -L --root=${BUILDCHROOT_DIR} ${KERNEL_DEP} | \
+                      grep "/lib/modules/.*/build")
+    fi
+}
-- 
2.16.4