[PATCH] build: Don't fetch tools/ioemu-dir unless needed

[George Dunlap <george.dunlap@eu.citrix.com>]

v3: more descriptive name for shared subdirs

c/s 18482 made both stubdom and tools dependent on tools/ioemu-dir
to fix a race condition where both build paths might try to fetch
qemu in parallel.  But this means that even if you build the tools
with CONFIG_IOEMU=n, qemu is still fetched first.

This patch causes tools/ioemu-dir to be a dependency for tools
only if CONFIG_IOEMU is enabled.

It's still unconditional for stubdoms, as it doesn't make much sense
to build stubdoms without it.

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

diff -r f9bb0bbea7c2 -r 8bb82569e8a4 Makefile
--- a/Makefile	Thu May 12 16:42:54 2011 +0100
+++ b/Makefile	Mon May 16 11:58:39 2011 +0100
@@ -13,6 +13,11 @@ SUBARCH := $(subst x86_32,i386,$(XEN_TAR
 export XEN_TARGET_ARCH SUBARCH XEN_SYSTYPE
 include buildconfigs/Rules.mk
 
+# If building with CONFIG_IOEMU, get ioemu-dir before building
+# tools or stubdom (or they may race)
+IOEMU_SHARED_SUBDIRS-y :=
+IOEMU_SHARED_SUBDIRS-$(CONFIG_IOEMU) += tools/ioemu-dir
+
 # build and install everything into the standard system directories
 .PHONY: install
 install: install-xen install-kernels install-tools install-stubdom install-docs
@@ -66,7 +71,7 @@ install-xen:
 	$(MAKE) -C xen install
 
 .PHONY: install-tools
-install-tools: tools/ioemu-dir
+install-tools: $(IOEMU_SHARED_SUBDIRS-y)
 	$(MAKE) -C tools install
 
 .PHONY: install-kernels
@@ -74,6 +79,7 @@ install-kernels:
 	for i in $(XKERNELS) ; do $(MAKE) $$i-install || exit 1; done
 
 .PHONY: install-stubdom
+# NB: depend on tools/ioemu-dir unconditionally for stubdoms
 install-stubdom: tools/ioemu-dir install-tools
 	$(MAKE) -C stubdom install
 ifeq (x86_64,$(XEN_TARGET_ARCH))