From 50ced5b3b108aba7f9b2c8e6f7de4e924f30f83b Mon Sep 17 00:00:00 2001
From: Stefan Weil <sw@weilnetz.de>
Date: Sat, 17 Dec 2011 09:27:39 +0100
Subject: [PATCH] configure: Improve Xen autodetection for hosts without Xen

With this patch, it only takes one test (instead of four)
to detect that there is no Xen support at all.

For most build hosts, this will reduce the time configure needs.
It will also reduce noisy output in config.log.

Build hosts with Xen now need up to five (instead of up to four)
tests. They get improved diagnostics when Xen support fails.

Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
---
 configure | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/configure b/configure
index 36ee849864..640e81536d 100755
--- a/configure
+++ b/configure
@@ -1317,10 +1317,30 @@ fi
 if test "$xen" != "no" ; then
   xen_libs="-lxenstore -lxenctrl -lxenguest"
 
-  # Xen unstable
+  # First we test whether Xen headers and libraries are available.
+  # If no, we are done and there is no Xen support.
+  # If yes, more tests are run to detect the Xen version.
+
+  # Xen (any)
   cat > $TMPC <<EOF
 #include <xenctrl.h>
 #include <xs.h>
+int main(void) {
+  return 0;
+}
+EOF
+  if ! compile_prog "" "$xen_libs" ; then
+    # Xen not found
+    if test "$xen" = "yes" ; then
+      feature_not_found "xen"
+    fi
+    xen=no
+
+  # Xen unstable
+  elif (
+      cat > $TMPC <<EOF
+#include <xenctrl.h>
+#include <xs.h>
 #include <stdint.h>
 #include <xen/hvm/hvm_info_table.h>
 #if !defined(HVM_MAX_VCPUS)
@@ -1336,7 +1356,8 @@ int main(void) {
   return 0;
 }
 EOF
-  if compile_prog "" "$xen_libs" ; then
+      compile_prog "" "$xen_libs"
+    ) ; then
     xen_ctrl_version=410
     xen=yes
 
@@ -1407,10 +1428,10 @@ EOF
     xen_ctrl_version=330
     xen=yes
 
-  # Xen not found or unsupported
+  # Xen version unsupported
   else
     if test "$xen" = "yes" ; then
-      feature_not_found "xen"
+      feature_not_found "xen (unsupported version)"
     fi
     xen=no
   fi