[PATCH] qemu: report issues causing the kvm probe to fail v3

[ehrhardt@linux.vnet.ibm.com]

From: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>

The patch applies to upstream qemu as well as kvm-userspace, but since it is
the qemu configure script I think it should go to upstream qemu (Anthony)
first and with the next merge to kvm-userspace. On the other hand it is the kvm
probe so an ack from Avi in case v3 is ok would be reasonable.

*updates*
v2 - it also reports other errors than just #error preprocessor statements
     (requested by Avi)
v3 - In case awk or grep is not installed it now gracfully (silently)
     fails still disabling kvm (requested by Anthony)

This patch is about reporting more details of the issue if configuring kvm
fails. Therefore this patch keeps the qemu style configure output which is a
list of "$Feature $Status", but extend the "no" result like "KVM Support no"
with some more information.

There might be a lot of things going wrong with that probe and I don't want
to handle all of them, but if it is one of the known checks e.g. for
KVM_API_VERSION then we could grep/awk that out and report it. The patch
reports in case of a known case in the style
"KVM support no - (Missing KVM capability KVM_CAP_DESTROY_MEMORY_REGION_WORKS)"

In case more than one #error is triggered it creates a comma separated list in
those brackets and in case it is something else than an #error it just reports
plain old "no".

Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
---

 configure |   27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/qemu/configure b/qemu/configure
--- a/qemu/configure
+++ b/qemu/configure
@@ -1002,13 +1002,17 @@ if test "$kvm" = "yes" ; then
 if test "$kvm" = "yes" ; then
     cat > $TMPC <<EOF
 #include <linux/kvm.h>
-#if !defined(KVM_API_VERSION) || \
-    KVM_API_VERSION < 12 || \
-    KVM_API_VERSION > 12 || \
-    !defined(KVM_CAP_USER_MEMORY) || \
-    !defined(KVM_CAP_SET_TSS_ADDR) || \
-    !defined(KVM_CAP_DESTROY_MEMORY_REGION_WORKS)
+#if !defined(KVM_API_VERSION) || KVM_API_VERSION < 12 || KVM_API_VERSION > 12
 #error Invalid KVM version
+#endif
+#if !defined(KVM_CAP_USER_MEMORY)
+#error Missing KVM capability KVM_CAP_USER_MEMORY
+#endif
+#if !defined(KVM_CAP_SET_TSS_ADDR)
+#error Missing KVM capability KVM_CAP_SET_TSS_ADDR
+#endif
+#if !defined(KVM_CAP_DESTROY_MEMORY_REGION_WORKS)
+#error Missing KVM capability KVM_CAP_DESTROY_MEMORY_REGION_WORKS
 #endif
 int main(void) { return 0; }
 EOF
@@ -1021,7 +1025,16 @@ EOF
       > /dev/null 2>/dev/null ; then
     :
   else
-    kvm="no"
+    kvm="no";
+    if [ -x "`which awk 2>/dev/null`" ] && \
+       [ -x "`which grep 2>/dev/null`" ]; then
+      kvmerr=`$cc $ARCH_CFLAGS -o $TMPE ${OS_CFLAGS} $kvm_cflags $TMPC 2>&1 \
+	| grep "error: " \
+	| awk -F "error: " '{if (NR>1) printf(", "); printf("%s",$2);}'`
+      if test "$kvmerr" != "" ; then
+        kvm="no - (${kvmerr})"
+      fi
+    fi
   fi
 fi