[Xen-devel] [PATCH] libxl: fix usage of backend parameter and run_hotplug_scripts

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

vif interfaces allows the user to specify the domain that should run
the backend (also known as driver domain) using the 'backend'
parameter. This is not compatible with run_hotplug_scripts=1, since
libxl can only run the hotplug scripts from the Domain 0.

Signed-off-by: Roger Pau Monne <roger.pau@xxxxxxxxxx>
---
 docs/misc/xl-network-configuration.markdown |    6 ++++--
 tools/libxl/libxl.c                         |   14 ++++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/docs/misc/xl-network-configuration.markdown 
b/docs/misc/xl-network-configuration.markdown
index 650926c..5e2f049 100644
--- a/docs/misc/xl-network-configuration.markdown
+++ b/docs/misc/xl-network-configuration.markdown
@@ -122,8 +122,10 @@ specified IP address to be used by the guest (blocking all 
others).
 ### backend
 
 Specifies the backend domain which this device should attach to. This
-defaults to domain 0. Specifying another domain requires setting up a
-driver domain which is outside the scope of this document.
+defaults to domain 0. This option does not work if `run_hotplug_scripts`
+is not disabled in xl.conf (see xl.conf(5) man page for more information
+on this option). Specifying another domain requires setting up a driver
+domain which is outside the scope of this document.
 
 ### rate
 
diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 8ea3478..6b85cdc 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -2474,6 +2474,8 @@ out:
 int libxl__device_nic_setdefault(libxl__gc *gc, libxl_device_nic *nic,
                                  uint32_t domid)
 {
+    int run_hotplug_scripts;
+
     if (!nic->mtu)
         nic->mtu = 1492;
     if (!nic->model) {
@@ -2503,6 +2505,18 @@ int libxl__device_nic_setdefault(libxl__gc *gc, 
libxl_device_nic *nic,
                                   libxl__xen_script_dir_path()) < 0 )
         return ERROR_FAIL;
 
+    run_hotplug_scripts = libxl__hotplug_settings(gc, XBT_NULL);
+    if (run_hotplug_scripts < 0) {
+        LOG(ERROR, "unable to get current hotplug scripts execution setting");
+        return run_hotplug_scripts;
+    }
+    if (nic->backend_domid != LIBXL_TOOLSTACK_DOMID && run_hotplug_scripts) {
+        LOG(ERROR, "the vif 'backend=' option cannot be used in conjunction "
+                   "with run_hotplug_scripts, please set run_hotplug_scripts "
+                   "to 0 in xl.conf");
+        return ERROR_FAIL;
+    }
+
     switch (libxl__domain_type(gc, domid)) {
     case LIBXL_DOMAIN_TYPE_HVM:
         if (!nic->nictype)
-- 
1.7.7.5 (Apple Git-26)


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