kernel: Enable custom kernel config additions

For some use cases, we may want to add additional kernel
configuration options (e.g. when adding AUFS). This commit
enables it by:
- renaming DEBUG to EXTRA
- append kernel_config${EXTRA} to the kernel config
- allowing passing in an EXTRA argument to the make file

Signed-off-by: Rolf Neugebauer <rolf.neugebauer@docker.com>

kernel/Dockerfile

@@ -31,7 +31,7 @@ RUN [ $(uname -m) == x86_64 ] && apk add libunwind-dev || true
 
 ARG KERNEL_VERSION
 ARG KERNEL_SERIES
-ARG DEBUG
+ARG EXTRA
 
 ENV KERNEL_SOURCE=https://www.kernel.org/pub/linux/kernel/v4.x/linux-${KERNEL_VERSION}.tar.xz
 ENV KERNEL_SHA256_SUMS=https://www.kernel.org/pub/linux/kernel/v4.x/sha256sums.asc
@@ -66,8 +66,7 @@ RUN set -e && for patch in /patches/*.patch; do \
     done
 
 # Kernel config
-COPY kernel_config-${KERNEL_SERIES}* /linux/
-COPY kernel_config.debug /linux/debug_config
+COPY kernel_config* /linux/
 
 RUN case $(uname -m) in \
     x86_64) \
@@ -78,15 +77,17 @@ RUN case $(uname -m) in \
         ;; \
     esac  && \
     cp /linux/kernel_config-${KERNEL_SERIES}-$(uname -m) ${KERNEL_DEF_CONF}; \
-    if [ -n "${DEBUG}" ]; then \
-        sed -i 's/CONFIG_PANIC_ON_OOPS=y/# CONFIG_PANIC_ON_OOPS is not set/' ${KERNEL_DEF_CONF}; \
-        sed -i "s/CONFIG_LOCALVERSION=\"-linuxkit\"/CONFIG_LOCALVERSION=\"-linuxkit${DEBUG}\"/" ${KERNEL_DEF_CONF}; \
-        cat /linux/debug_config >> ${KERNEL_DEF_CONF}; \
+    if [ -n "${EXTRA}" ]; then \
+        sed -i "s/CONFIG_LOCALVERSION=\"-linuxkit\"/CONFIG_LOCALVERSION=\"-linuxkit${EXTRA}\"/" ${KERNEL_DEF_CONF}; \
+        if [ "${EXTRA}" = "-dbg" ]; then \
+            sed -i 's/CONFIG_PANIC_ON_OOPS=y/# CONFIG_PANIC_ON_OOPS is not set/' ${KERNEL_DEF_CONF}; \
+        fi && \
+        cat /linux/kernel_config${EXTRA} >> ${KERNEL_DEF_CONF}; \
     fi && \
-    rm /linux/kernel_config-${KERNEL_SERIES}* && \
+    rm /linux/kernel_config* && \
     make defconfig && \
     make oldconfig && \
-    if [ -z "${DEBUG}" ]; then diff .config ${KERNEL_DEF_CONF}; fi
+    if [ -z "${EXTRA}" ]; then diff .config ${KERNEL_DEF_CONF}; fi
 
 RUN mkdir /out
 
@@ -101,7 +102,7 @@ RUN make -j "$(getconf _NPROCESSORS_ONLN)" KCFLAGS="-fno-pie" && \
         ;; \
     esac && \
     cp System.map /out && \
-    ([ -n "${DEBUG}" ] && cp vmlinux /out || true)
+    ([ "${EXTRA}" = "-dbg" ] && cp vmlinux /out || true)
 
 # WireGuard
 RUN curl -sSL -o /wireguard.tar.xz "${WIREGUARD_URL}" && \

kernel/Makefile

@@ -17,6 +17,11 @@ ORG?=linuxkit
 IMAGE:=kernel
 IMAGE_PERF:=kernel-perf
 
+# You can specify an extra options for the Makefile. This will:
+# - append a kernel_config$(EXTRA) to the kernel config for your kernel/arch
+# - append $(EXTRA) to the CONFIG_LOCALVERSION of your kernel
+EXTRA?=
+
 ifeq ($(HASH),)
 HASH_COMMIT?=HEAD # Setting this is only really useful with the show-tag target
 HASH?=$(shell git ls-tree --full-tree $(HASH_COMMIT) -- $(CURDIR) | awk '{print $$3}')
@@ -87,12 +92,12 @@ sources/linux-$(1).tar.xz: Makefile | sources
 KERNEL_VERSIONS+=$(1)
 endif
 
-build_$(2)$(3): Dockerfile Makefile $(wildcard patches-$(2)/*) $(wildcard kernel_config-$(2)*) kernel_config.debug | sources
+build_$(2)$(3): Dockerfile Makefile $(wildcard patches-$(2)/*) $(wildcard kernel_config-$(2)*) kernel_config-dbg | sources
 	docker pull $(ORG)/$(IMAGE):$(1)$(3)-$(TAG)$(SUFFIX) || \
 		docker build \
 			--build-arg KERNEL_VERSION=$(1) \
 			--build-arg KERNEL_SERIES=$(2) \
-			--build-arg DEBUG=$(3) \
+			--build-arg EXTRA=$(3) \
 			$(LABELS) \
 			--no-cache -t $(ORG)/$(IMAGE):$(1)$(3)-$(TAG)$(SUFFIX) .
 
@@ -139,11 +144,11 @@ endef
 # Build Targets
 # Debug targets only for latest stable and LTS stable
 #
-$(eval $(call kernel,4.12.8,4.12.x))
+$(eval $(call kernel,4.12.8,4.12.x,$(EXTRA)))
 $(eval $(call kernel,4.12.8,4.12.x,-dbg))
-$(eval $(call kernel,4.9.44,4.9.x))
+$(eval $(call kernel,4.9.44,4.9.x,$(EXTRA)))
 $(eval $(call kernel,4.9.44,4.9.x,-dbg))
-$(eval $(call kernel,4.4.83,4.4.x))
+$(eval $(call kernel,4.4.83,4.4.x,$(EXTRA)))
 
 # Target for kernel config
 kconfig: | sources