tools: provide explicit target for refetching/resetting qemu

This patch adds an explicit update mechanism:
  make tools/ioemu-dir-force-update
This isn't brilliant but is better than doing "cd tools/ioemu-remote
&& git reset --hard <sha1...>" by hand.

Note that invoking this target will destroy all working tree changes
made to qemu-xen.

Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

Makefile

@@ -83,6 +83,10 @@ endif
 tools/ioemu-dir:
 	$(MAKE) -C tools ioemu-dir-find
 
+.PHONY: tools/ioemu-dir-force-update
+tools/ioemu-dir-force-update:
+	$(MAKE) -C tools ioemu-dir-force-update
+
 .PHONY: install-docs
 install-docs:
 	sh ./docs/check_pkgs && $(MAKE) -C docs install || true

tools/Makefile

@@ -117,6 +117,14 @@ ioemu-dir-find:
 		cd ioemu-dir; \
 		./xen-setup $(IOEMU_CONFIGURE_CROSS)
 
+.PHONY: ioemu-dir-force-update
+ioemu-dir-force-update:
+	set -ex; \
+	if [ "$(QEMU_TAG)" ]; then \
+		cd ioemu-remote; \
+		$(GIT) reset --hard $(QEMU_TAG); \
+	fi
+
 subdir-all-ioemu-dir subdir-install-ioemu-dir: ioemu-dir-find
 
 subdir-clean-ioemu-dir: