snap: Build and package rust version of virtiofsd

Update the snap config file to build the rust version of `virtiofsd` for
x86_64, but build QEMU's C version for other platforms.

Fixes: #4261.

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

snap/snapcraft.yaml

@@ -317,6 +317,41 @@ parts:
       # Hack: move qemu to /
       "snap/kata-containers/current/": "./"
 
+  virtiofsd:
+    plugin: nil
+    after: [godeps]
+    override-build: |
+      # Currently, only one platform uses the new rust virtiofsd. The
+      # others make use of QEMU's C implementation.
+      #
+      # See "tools/packaging/scripts/configure-hypervisor.sh".
+      if [ "$(uname -m)" = 'x86_64' ]
+      then
+          echo "INFO: Building rust version of virtiofsd"
+      else
+          echo "INFO: Building QEMU's C version of virtiofsd"
+          # Handled by the 'qemu' part, so nothing more to do here.
+          exit 0
+      fi
+
+      # put everything in stage
+      cd ${SNAPCRAFT_STAGE}
+
+      export PATH="$PATH:${SNAPCRAFT_STAGE}/bin"
+      export GOPATH=${SNAPCRAFT_STAGE}/gopath
+
+      kata_dir=${GOPATH}/src/github.com/${SNAPCRAFT_PROJECT_NAME}/${SNAPCRAFT_PROJECT_NAME}
+      cd "${kata_dir}"
+      # Download the rust implementation of virtiofsd
+      tools/packaging/static-build/virtiofsd/build-static-virtiofsd.sh
+      sudo install \
+        --owner='root' \
+        --group='root' \
+        --mode=0755 \
+        -D \
+        --target-directory="${SNAPCRAFT_PART_INSTALL}/usr/libexec/" \
+        virtiofsd/virtiofsd
+
   cloud-hypervisor:
     plugin: nil
     after: [godeps]