Add rm-docker-linux package that pre-builds linux

Optimizes the builds by not re-building the kernel if not needed.

Author: timower

.github/workflows/docker-image.yml

@@ -2,7 +2,6 @@ name: Docker Image CI
 
 on:
   push:
-    branches: [ "main", "dev" ]
   pull_request:
     branches: [ "main" ]
 
@@ -11,8 +10,40 @@ env:
   IMAGE_NAME: ${{ github.repository }}
 
 jobs:
+  build-linux:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}-linux
+
+      - name: Build
+        uses: docker/build-push-action@v5
+        with:
+          push: ${{ github.event_name != 'pull_request' && github.ref_name == 'main' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          target: linux-build
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
   build:
     runs-on: ubuntu-latest
+    needs: [build-linux]
     permissions:
       contents: read
       packages: write

Dockerfile

@@ -4,8 +4,12 @@ ARG rm2_stuff_tag=v0.1.2
 ARG fw_version=3.5.2.1807
 ARG linux_release=5.8.18
 
+# By default use a cached linux kernel. To build locally pass:
+#  --build-arg linux_image=linux-build
+ARG linux_image=ghcr.io/timower/rm-docker-linux:linux-image
+
 # Step 1: Build Linux for the emulator
-FROM $toltec_image as linux-build
+FROM $toltec_image as linux-builder
 
 RUN apt-get update && \
     apt-get install -y bison bc lzop libssl-dev flex
@@ -33,6 +37,13 @@ RUN make O=imx7 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -j $(nproc) && \
     cp imx7/arch/arm/boot/dts/imx7d-rm.dtb /opt && \
     rm -rf imx7
 
+# This container just needs to kernel and device tree
+FROM scratch AS linux-build
+COPY --from=linux-builder /opt/zImage /opt/imx7d-rm.dtb /
+
+# Dummy stage to use in the arg below
+FROM $linux_image AS linux-image
+
 # Step 2: rootfs
 FROM linuxkit/guestfs:f85d370f7a3b0749063213c2dd451020e3a631ab AS rootfs
 
@@ -69,8 +80,8 @@ RUN apt-get update && \
 
 RUN mkdir -p /opt/root
 
-COPY --from=linux-build /opt/zImage /opt
-COPY --from=linux-build /opt/imx7d-rm.dtb /opt
+COPY --from=linux-image /zImage /opt
+COPY --from=linux-image /imx7d-rm.dtb /opt
 COPY --from=rootfs /opt/rootfs.qcow2 /opt/root
 
 ADD bin /opt/bin