[libvirt] [FOR 1.3.0 PATCH] conf: add net device prefix for Xen

[Jim Fehlig]

In commit d2e5538b1, the libxl driver was changed to copy interface
names autogenerated by libxl to the corresponding network def in the
domain's virDomainDef object. The copied name is freed when the domain
transitions to the shutoff state. But when migrating a domain, the
autogenerated name is included in the XML sent to the destination host.
It is possible an interface with the same name already exists on the
destination host, causing migration to fail. Indeed the Xen project's
OSSTEST CI already encountered such a failure.

This patch defines another VIR_NET_GENERATED_PREFIX for Xen, allowing
the autogenerated names to be excluded when parsing and formatting
inactive config.

Signed-off-by: Jim Fehlig <jfehlig at suse.com>
---

This is an alternative approach to Joao's fix for this regression

https://www.redhat.com/archives/libvir-list/2015-December/msg00197.html

I think it is the same approach used by the qemu driver. My only
reservation is that it expands the potential for clashes with
user-defined names. I.e. with this change both 'vnet' and 'vif' are
reserved prefixes.

 src/conf/domain_conf.c   | 6 ++++--
 src/conf/domain_conf.h   | 4 ++++
 src/libxl/libxl_domain.c | 5 +++--
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 2f5c0ed..debcf4e 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -8428,7 +8428,8 @@ virDomainNetDefParseXML(virDomainXMLOptionPtr xmlopt,
                 ifname = virXMLPropString(cur, "dev");
                 if (ifname &&
                     (flags & VIR_DOMAIN_DEF_PARSE_INACTIVE) &&
-                    STRPREFIX(ifname, VIR_NET_GENERATED_PREFIX)) {
+                    (STRPREFIX(ifname, VIR_NET_GENERATED_PREFIX) ||
+                     STRPREFIX(ifname, VIR_NET_GENERATED_PREFIX_XEN))) {
                     /* An auto-generated target name, blank it out */
                     VIR_FREE(ifname);
                 }
@@ -19790,7 +19791,8 @@ virDomainNetDefFormat(virBufferPtr buf,
     virBufferEscapeString(buf, "<backenddomain name='%s'/>\n", def->domain_name);
     if (def->ifname &&
         !((flags & VIR_DOMAIN_DEF_FORMAT_INACTIVE) &&
-          (STRPREFIX(def->ifname, VIR_NET_GENERATED_PREFIX)))) {
+          (STRPREFIX(def->ifname, VIR_NET_GENERATED_PREFIX) ||
+           STRPREFIX(def->ifname, VIR_NET_GENERATED_PREFIX_XEN)))) {
         /* Skip auto-generated target names for inactive config. */
         virBufferEscapeString(buf, "<target dev='%s'/>\n", def->ifname);
     }
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 90d8e13..d2cc26f 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1085,6 +1085,10 @@ struct _virDomainNetDef {
  * by libvirt, and cannot be used for a persistent network name.  */
 # define VIR_NET_GENERATED_PREFIX "vnet"
 
+/* Used for prefix of ifname of any network name generated dynamically
+ * by libvirt for Xen, and cannot be used for a persistent network name.  */
+# define VIR_NET_GENERATED_PREFIX_XEN "vif"
+
 typedef enum {
     VIR_DOMAIN_CHR_DEVICE_STATE_DEFAULT = 0,
     VIR_DOMAIN_CHR_DEVICE_STATE_CONNECTED,
diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c
index ef92974..c5d84a4 100644
--- a/src/libxl/libxl_domain.c
+++ b/src/libxl/libxl_domain.c
@@ -734,7 +734,7 @@ libxlDomainCleanup(libxlDriverPrivatePtr driver,
         for (i = 0; i < vm->def->nnets; i++) {
             virDomainNetDefPtr net = vm->def->nets[i];
 
-            if (STRPREFIX(net->ifname, "vif"))
+            if (STRPREFIX(net->ifname, VIR_NET_GENERATED_PREFIX_XEN))
                 VIR_FREE(net->ifname);
         }
     }
@@ -918,7 +918,8 @@ libxlDomainCreateIfaceNames(virDomainDefPtr def, libxl_domain_config *d_config)
         if (net->ifname)
             continue;
 
-        ignore_value(virAsprintf(&net->ifname, "vif%d.%d%s",
+        ignore_value(virAsprintf(&net->ifname,
+                                 VIR_NET_GENERATED_PREFIX_XEN "%d.%d%s",
                                  def->id, x_nic->devid, suffix));
     }
 }
-- 
2.6.1