contrib: Notes and build support for crosvm

crosvm is a VMM written on Rust which can run the device
backends in secomp isolated processes.

This adds build support for crosvm for x86 and arm64 as well
as some instructions on how to run LinuxKit built images on crosvm.

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

contrib/crosvm/Dockerfile

@@ -0,0 +1,36 @@
+FROM rust:1.25.0-stretch
+
+ENV CROSVM_REPO=https://chromium.googlesource.com/chromiumos/platform/crosvm
+ENV CROSVM_COMMIT=7a7268faf0a43c79b6a4520f5c2f35c3e0233932
+ENV MINIJAIL_REPO=https://android.googlesource.com/platform/external/minijail
+ENV MINIJAIL_COMMIT=d45fc420bb8fd9d1fc9297174f3c344db8c20bbd
+
+# Install deps
+RUN apt-get update && apt-get install -y libcap-dev libfdt-dev
+
+# Get source code
+RUN git clone ${MINIJAIL_REPO} && \
+    cd /minijail && \
+    git checkout ${MINIJAIL_COMMIT} && \
+    cd / && \
+    git clone ${CROSVM_REPO} && \
+    cd crosvm && \
+    git checkout ${CROSVM_COMMIT}
+
+# Compile and install minijail
+WORKDIR /minijail
+RUN make && \
+    cp libminijail.so /usr/lib/ && \
+    cp libminijail.h /usr/include/
+
+# Compile crosvm
+WORKDIR /crosvm
+RUN cargo build --release
+    
+RUN mkdir /out && \
+    cp /minijail/libminijail.so /out && \
+    cp /crosvm/target/release/crosvm /out && \
+    cp -r /crosvm/seccomp /out
+
+WORKDIR /out
+ENTRYPOINT ["tar", "cf", "-", "libminijail.so", "crosvm", "seccomp"]