[libvirt] [PATCH] libxl: allow an <emulator> to be selected in the domain config XML

[David Scott]

The emulator path supplied can be any valid path on the system.

Note that when setting a device_model, libxl needs us to set the
device_model_version too. The device_model_version can be either

  ...QEMU_XEN: meaning "upstream qemu", the default in xen-4.3 onwards
  ...QEMU_XEN_TRADITIONAL: the old xen-specific fork

We detect the device_model_version by examining the qemu filename:
if it is "qemu-dm" then it's the old xen-specific fork. If anything
else then we assume "upstream qemu" (whose filename may change
in future). Note that if you are using a wrapper script to (eg)
adjust the arguments of the old qemu during development, you will
have to ensure the wrapper script also has the name "qemu-dm", by
placing it in a separate directory.

Signed-off-by: David Scott <dave.scott at eu.citrix.com>
---
 src/libxl/libxl_conf.c |   44 ++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 44 insertions(+), 0 deletions(-)

diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
index 7e0753a..2aa5a62 100644
--- a/src/libxl/libxl_conf.c
+++ b/src/libxl/libxl_conf.c
@@ -788,6 +788,46 @@ libxlMakeCapabilities(libxl_ctx *ctx)
 }
 
 int
+libxlMakeEmulator(virDomainDefPtr def, libxl_domain_config *d_config)
+{
+    /* No explicit override means use the default */
+    if (!def->emulator) {
+        return 0;
+    }
+
+    if (!virFileExists(def->emulator)) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("emulator '%s' not found"),
+                       def->emulator);
+        return -1;
+    }
+
+    VIR_FREE(d_config->b_info.device_model);
+    if ((d_config->b_info.device_model = strdup(def->emulator)) == NULL) {
+        virReportOOMError();
+        return -1;
+    }
+
+    /* N.B. from xen/tools/libxl/libxl_types.idl:
+     * "If setting device_model you must set device_model_version too."
+     *
+     * The xen-4.3 and later default is "upstream qemu" (QEMU_XEN)
+     * so we make that the default and special-case the old-style
+     * "traditional qemu" (QEMU_XEN_TRADITIONAL)
+     */
+
+    d_config->b_info.device_model_version =
+        LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN;
+
+    if (STREQ(basename(def->emulator), "qemu-dm"))
+        d_config->b_info.device_model_version =
+            LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL; 
+
+    return 0;
+}
+
+
+int
 libxlBuildDomainConfig(libxlDriverPrivatePtr driver,
                        virDomainDefPtr def, libxl_domain_config *d_config)
 {
@@ -811,6 +851,10 @@ libxlBuildDomainConfig(libxlDriverPrivatePtr driver,
         goto error;
     }
 
+    if (libxlMakeEmulator(def, d_config) < 0) {
+        goto error;
+    }
+
     d_config->on_reboot = def->onReboot;
     d_config->on_poweroff = def->onPoweroff;
     d_config->on_crash = def->onCrash;
-- 
1.7.1