build: Add TRACE_DEV_MODE option to redirect the guest journal

Add a `TRACE_DEV_MODE=yes` build option. This will install a new systemd
service and snippet to allow the guest OS journal to be redirected back
to the host using VSOCK.

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

Makefile

@@ -34,9 +34,17 @@ ifeq ($(TRACE),yes)
   endif
 endif
 
+# If "yes", install additional services to redirect guest OS journal messages
+# to the host using VSOCK.
+TRACE_DEV_MODE := no
+
 # Path to systemd unit directory if installed as not init.
 UNIT_DIR := /usr/lib/systemd/system
 
+# Path to systemd drop-in snippet directory used to override the agent's
+# service without having to modify the pristine agent service file.
+SNIPPET_DIR := /etc/systemd/system/$(AGENT_SERVICE).d/
+
 GENERATED_FILES :=
 # Define if agent will be built by seccomp tag
 SECCOMP := no
@@ -53,6 +61,11 @@ ifeq ($(TRACE),yes)
 UNIT_FILES += jaeger-client-socat-redirector.service
 endif
 
+ifeq ($(TRACE_DEV_MODE),yes)
+UNIT_FILES += kata-journald-host-redirect.service
+SNIPPET_FILES += kata-redirect-agent-output-to-journal.conf
+endif
+
 VERSION_FILE := ./VERSION
 VERSION := $(shell grep -v ^\# $(VERSION_FILE))
 COMMIT_NO := $(shell git rev-parse HEAD 2> /dev/null || true)
@@ -83,6 +96,11 @@ ifeq ($(INIT),no)
 	@echo "Installing systemd unit files..."
 	$(foreach f,$(UNIT_FILES),$(call INSTALL_FILE,$f,$(UNIT_DIR)))
 endif
+ifeq ($(TRACE_DEV_MODE),yes)
+	@echo "Installing systemd snippet files..."
+	@mkdir -p $(SNIPPET_DIR)
+	$(foreach f,$(SNIPPET_FILES),$(call INSTALL_FILE,$f,$(SNIPPET_DIR)))
+endif
 
 build-image:
 	# build an docker image for development