commit 400e716d7d8371fa718c27bb4f05b9a68929e64a
Author: Jim Fehlig <jfehlig@suse.com>
Date:   Thu May 12 14:40:28 2016 -0600

    libxl: don't attempt to probe a non-existent emulator
    
    When probing the <emulator> with '-help' to determine if
    it is the old qemu, errors are reported if the emulator
    doesn't exist
    
    libvirt:  error : internal error: Child process
    (/usr/lib/xen/bin/qemu-dm -help) unexpected exit status 127:
    libvirt:  error : cannot execute binary /usr/lib/xen/bin/qemu-dm:
    No such file or directory
    
    Avoid the probe if the specified emulator doesn't exist,
    squelching the error. There is no behavior change since
    libxlDomainGetEmulatorType() would return
    LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN if the probe failed
    via virCommandRun().
    
    Signed-off-by: Jim Fehlig <jfehlig@suse.com>

Index: libvirt-1.3.4/src/libxl/libxl_conf.c
===================================================================
--- libvirt-1.3.4.orig/src/libxl/libxl_conf.c
+++ libvirt-1.3.4/src/libxl/libxl_conf.c
@@ -916,6 +916,9 @@ libxlDomainGetEmulatorType(const virDoma
 
     if (def->os.type == VIR_DOMAIN_OSTYPE_HVM) {
         if (def->emulator) {
+            if (!virFileExists(def->emulator))
+                goto cleanup;
+
             cmd = virCommandNew(def->emulator);
 
             virCommandAddArgList(cmd, "-help", NULL);