[RFC PATCH] tests/vm: avoid re-building the VM images all the time

["Alex Bennée" <alex.bennee@linaro.org>]

There are two problems.

The first is a .PHONY target will always evaluate which triggers a
full re-build of the VM images. Drop the requirement knowing that this
introduces a manual step on freshly configure build dirs.

The second is a minor unrelated tweak to the Makefile also triggers an
expensive full re-build. Solve this be avoiding the dependency and
putting a comment just above the bit that matters and hope developers
notice the comment.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---

This is hacky and sub-optimal. There surely must be a way to have our cake
and eat it?
---
 tests/vm/Makefile.include | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/tests/vm/Makefile.include b/tests/vm/Makefile.include
index bf12e0fa3c5..a109773c588 100644
--- a/tests/vm/Makefile.include
+++ b/tests/vm/Makefile.include
@@ -88,10 +88,11 @@ vm-build-all: $(addprefix vm-build-, $(IMAGES))
 vm-clean-all:
 	rm -f $(IMAGE_FILES)
 
+# Rebuilding the VMs every time this Makefile is tweaked is very
+# expensive for most users. If you tweak the recipe bellow you will
+# need to manually zap $(IMAGES_DIR)/%.img to rebuild.
 $(IMAGES_DIR)/%.img:	$(SRC_PATH)/tests/vm/% \
-			$(SRC_PATH)/tests/vm/basevm.py \
-			$(SRC_PATH)/tests/vm/Makefile.include \
-			$(VM_VENV)
+			$(SRC_PATH)/tests/vm/basevm.py
 	@mkdir -p $(IMAGES_DIR)
 	$(call quiet-command, \
 		$(VM_PYTHON) $< \
-- 
2.39.2