[PATCH v3 2/2] systemd: avoid string comparisons on dbus error messages

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

Add a virDBusErrorIsUnknownMethod helper so that callers
don't need todo string comparisons themselves to detect
standard error names.
---
 src/libvirt_private.syms | 1 +
 src/util/virdbus.c       | 9 +++++++++
 src/util/virdbus.h       | 2 ++
 src/util/virsystemd.c    | 3 +--
 4 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 528e93c..a8cd87f 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1244,6 +1244,7 @@ virDBusCreateMethod;
 virDBusCreateMethodV;
 virDBusCreateReply;
 virDBusCreateReplyV;
+virDBusErrorIsUnknownMethod;
 virDBusGetSessionBus;
 virDBusGetSystemBus;
 virDBusHasSystemBus;
diff --git a/src/util/virdbus.c b/src/util/virdbus.c
index 3522ae0..1cf1eef 100644
--- a/src/util/virdbus.c
+++ b/src/util/virdbus.c
@@ -1894,3 +1894,12 @@ void virDBusMessageUnref(DBusMessage *msg ATTRIBUTE_UNUSED)
     /* nothing */
 }
 #endif /* ! WITH_DBUS */
+
+bool virDBusErrorIsUnknownMethod(virErrorPtr err)
+{
+    return err->domain == VIR_FROM_DBUS &&
+        err->code == VIR_ERR_DBUS_SERVICE &&
+        err->level == VIR_ERR_ERROR &&
+        STREQ_NULLABLE("org.freedesktop.DBus.Error.UnknownMethod",
+                       err->str1);
+}
diff --git a/src/util/virdbus.h b/src/util/virdbus.h
index e2b8d2b..9e86538 100644
--- a/src/util/virdbus.h
+++ b/src/util/virdbus.h
@@ -74,4 +74,6 @@ void virDBusMessageUnref(DBusMessage *msg);
 
 int virDBusIsServiceEnabled(const char *name);
 int virDBusIsServiceRegistered(const char *name);
+
+bool virDBusErrorIsUnknownMethod(virErrorPtr err);
 #endif /* __VIR_DBUS_H__ */
diff --git a/src/util/virsystemd.c b/src/util/virsystemd.c
index 6de265b..3ac399a 100644
--- a/src/util/virsystemd.c
+++ b/src/util/virsystemd.c
@@ -281,8 +281,7 @@ int virSystemdCreateMachine(const char *name,
             goto cleanup;
 
         if (error.level == VIR_ERR_ERROR) {
-            if (STREQ_NULLABLE("org.freedesktop.DBus.Error.UnknownMethod",
-                               error.str1)) {
+            if (virDBusErrorIsUnknownMethod(&error)) {
                 VIR_INFO("CreateMachineWithNetwork isn't supported, switching "
                          "to legacy CreateMachine method for systemd-machined");
                 virResetError(&error);
-- 
2.1.0

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