pkg/firmware: Add a package with firmware required by enabled device drivers

This new 'firmware' package contains the firmware blobs required
by the device drivers in a LinuxKit kernel. The list of required
blobs is determined by calling 'modinfo' on each module.

We also unconditionally include the AMD CPU microcode and the
licence files.

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

pkg/firmware/Dockerfile

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+# Make modules from a recentish kernel available
+FROM linuxkit/kernel:4.14.12 AS kernel
+
+FROM linuxkit/alpine:34518265c6cb63ff02074549cc5b64bef40c336f AS build
+RUN apk add --no-cache git kmod
+
+# Clone the firmware repository
+# Make sure you also update the FW_COMMIT in ../firmware-all/Dockerfile
+ENV FW_URL=git://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git
+ENV FW_COMMIT=65b1c68c63f974d72610db38dfae49861117cae2
+WORKDIR /
+RUN git clone ${FW_URL} && \
+    cd /linux-firmware && \
+    git checkout ${FW_COMMIT}
+
+# Copy files we always need/want: Licenses, docs and AMD CPU microcode
+WORKDIR /linux-firmware
+RUN set -e && \
+    mkdir -p /out/lib/firmware && \
+    cp README WHENCE /out/lib/firmware && \
+    cp GPL-? LICENSE.* LICENCE.* /out/lib/firmware && \
+    case $(uname -m) in \
+    x86_64) \
+        cp -r amd-ucode /out/lib/firmware; \
+        ;; \
+    esac
+
+# Extract kernel modules for
+WORKDIR /
+COPY --from=kernel /kernel.tar /kernel.tar
+RUN tar xf /kernel.tar
+
+# Copy files required by the modules
+RUN set -e && \
+    for fw in $(find /lib/modules -name \*.ko -exec modinfo --field=firmware {} \;); do \
+        mkdir -p "/out/lib/firmware/$fw" && \
+        cp "/linux-firmware/$fw" "/out/lib/firmware/$fw"; \
+    done
+
+FROM scratch
+WORKDIR /
+ENTRYPOINT []
+COPY --from=build /out/lib/ /lib/
+

pkg/firmware/README.md

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+The `firmware` package contains updated firmware files required by any
+driver compiled as a module. Based on the modules included in a recent
+LinuxKit kernel, copy the required firmware binaries as reported by
+'modinfo'. We deliberately do *not* pick the latest version here to
+prevent it being updated on kernel updates. Firmware revisions do not
+change very often and we expect older and newer kernels to work with a
+range of firmware binaries.
+
+Note: The current mechanism only handles firmware blobs required by
+modules and ignores firmware blobs required by drivers compiled into
+the kernel. However, with the LinuxKit kernels we typically compile
+all hardware drivers as modules.

pkg/firmware/build.yml

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+image: firmware
+network: true