make: Make "src-tarball" target actually make a source tarball

At the moment, making a release tarball is an annoyingly manual
process that involves running "git archive" into a temporary directory.

Script this process up and make a target, so that the release manager
can simply type "make src-tarball-release" and have everything show up
nice and neat in dist/xen-$version.tar.gz.  "make src-tarball" will
make a version number based on git describe, which will typically have
the most recent tag, number of commits since that tag, and the git
commit id of the current HEAD.

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>

Makefile

@@ -143,6 +143,23 @@ subtree-force-update:
 subtree-force-update-all:
 	$(MAKE) -C tools subtree-force-update-all
 
+# Make a source tarball, including qemu sub-trees.
+#
+# src-tarball will use "git describe" for the version number.  This
+# will have the most recent tag, number of commits since that tag, and
+# git commit id of the head.  This is suitable for a "snapshot"
+# tarball of an unreleased tree.
+#
+# src-tarball-release will use "make xenversion" as the version
+# number.  This is suitable for release tarballs.
+.PHONY: src-tarball-release
+src-tarball-release: subtree-force-update-all
+	bash ./tools/misc/mktarball $(XEN_ROOT) $$($(MAKE) -C xen xenversion --no-print-directory)
+
+.PHONY: src-tarball
+src-tarball: subtree-force-update-all
+	bash ./tools/misc/mktarball $(XEN_ROOT) $$(git describe)
+
 .PHONY: clean
 clean::
 	$(MAKE) -C xen clean
@@ -171,13 +188,6 @@ endif
 .PHONY: mrproper
 mrproper: distclean
 
-# Prepare for source tarball
-.PHONY: src-tarball
-src-tarball: distclean
-	$(MAKE) -C xen .banner
-	rm -rf xen/tools/figlet .[a-z]*
-	$(MAKE) -C xen distclean
-
 .PHONY: help
 help:
 	@echo 'Installation targets:'
@@ -211,6 +221,10 @@ help:
 	@echo '  install-tboot         - download, build, and install the tboot module'
 	@echo '  clean-tboot           - clean the tboot module if it exists'
 	@echo
+	@echo 'Package targets:'
+	@echo '  src-tarball-release   - make a source tarball with xen and qemu tagged with a release'
+	@echo '  src-tarball           - make a source tarball with xen and qemu tagged with git describe'
+	@echo
 	@echo 'Environment:'
 	@echo '  [ this documentation is sadly not complete ]'