[Libguestfs] [PATCH 2/2] lib: appliance: qemu 2.9.0 supports TCG with -cpu host on x86 (RHBZ#1277744).

[Richard W.M. Jones]

Starting with version 2.9.0, qemu can use:

  qemu-system-x86_64 -M accel=tcg -cpu host

without breaking.  This only applies to x86 (i386 or x86_64) at the
moment.  If we detect these conditions, pass -cpu host
unconditionally.

This should hopefully address problems where other hypervisors
(eg. VirtualBox) are running, which breaks KVM in a way that we cannot
detect, and consequently breaks libguestfs.
---
 src/appliance-cpu.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/appliance-cpu.c b/src/appliance-cpu.c
index a7cf1eb..fa7e941 100644
--- a/src/appliance-cpu.c
+++ b/src/appliance-cpu.c
@@ -63,7 +63,7 @@
  *
  * We don't know for sure if KVM will work, but C<-cpu host> is broken
  * with TCG, so we almost always pass a broken C<-cpu> flag if KVM is
- * semi-broken in any way.
+ * semi-broken in any way.  (This is fixed in qemu 2.9, thanks Eduardo!)
  *
  * =back
  */
@@ -77,6 +77,14 @@ guestfs_int_get_cpu_model (int kvm, const struct version *qemu_version)
   else
     return "cortex-a57";
 #else
+#if defined(__i386__) || defined(__x86_64__)
+  /* Eduardo added the ability to use -cpu host with TCG on x86 in
+   * qemu 2.9.
+   */
+  if (guestfs_int_version_ge (qemu_version, 2, 9, 0))
+    return "host";
+  /* otherwise fallthrough */
+#endif
   /* On most architectures, it is faster to pass the CPU host model to
    * the appliance, allowing maximum speed for things like checksums
    * and encryption.  Only do this with KVM.  It is broken in subtle
-- 
2.10.2