[Qemu-devel] [PATCH] qom: avoid reporting errors for NULL error object

["Daniel P. Berrangé" <berrange@redhat.com>]

When debugging QEMU it is often useful to put a breakpoint on the
error_setg_internal method impl.

Unfortunately the object_property_add / object_class_property_add
methods call object_property_find / object_class_property_find methods
to check if a property exists already before adding the new property.

As a result there are a huge number of calls to error_setg_internal
on startup of most QEMU commands, making it very painful to set a
breakpoint on this method.

This puts a minor optimization on the code so that we avoid calling
error_setg() when errp is NULL. Functionally there's no difference
since error_setg() is a no-op when errp is NULL, but this lets us
use breakpoints in GDB in a practical way.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 qom/object.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/qom/object.c b/qom/object.c
index 547dcf97c3..ddd5e7a30e 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -1087,7 +1087,12 @@ ObjectProperty *object_property_find(Object *obj, const char *name,
         return prop;
     }
 
-    error_setg(errp, "Property '.%s' not found", name);
+    /* Optimized to avoid calling error_setg if errp == NULL
+     * otherwise every property add call hits error_setg
+     * making it impratical to set breakpoints in GDB */
+    if (errp) {
+        error_setg(errp, "Property '.%s' not found", name);
+    }
     return NULL;
 }
 
@@ -1133,7 +1138,10 @@ ObjectProperty *object_class_property_find(ObjectClass *klass, const char *name,
     }
 
     prop = g_hash_table_lookup(klass->properties, name);
-    if (!prop) {
+    /* Optimized to avoid calling error_setg if errp == NULL
+     * otherwise every property add call hits error_setg
+     * making it impratical to set breakpoints in GDB */
+    if (!prop && errp) {
         error_setg(errp, "Property '.%s' not found", name);
     }
     return prop;
-- 
2.19.1