hostmem: add more information in error messages

When there are multiple memory backends in use, including the object type
and property name in the error message can help users to locate the error.
Signed-off-by: NHaozhong Zhang <haozhong.zhang@intel.com>
Signed-off-by: NZhang Yi <yi.z.zhang@linux.intel.com>
Message-Id: <97d9193875747d8378c05b9e3b3cb39c1b7d2b4e.1546399191.git.yi.z.zhang@linux.intel.com>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>
[ehabkost: reword commit message]
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

backends/hostmem-file.c

@@ -82,7 +82,8 @@ static void set_mem_path(Object *o, const char *str, Error **errp)
     HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
 
     if (host_memory_backend_mr_inited(backend)) {
-        error_setg(errp, "cannot change property value");
+        error_setg(errp, "cannot change property 'mem-path' of %s",
+                   object_get_typename(o));
         return;
     }
     g_free(fb->mem_path);
@@ -120,7 +121,8 @@ static void file_memory_backend_set_align(Object *o, Visitor *v,
     uint64_t val;
 
     if (host_memory_backend_mr_inited(backend)) {
-        error_setg(&local_err, "cannot change property value");
+        error_setg(&local_err, "cannot change property '%s' of %s",
+                   name, object_get_typename(o));
         goto out;
     }
 

backends/hostmem.c

@@ -57,7 +57,8 @@ host_memory_backend_set_size(Object *obj, Visitor *v, const char *name,
     uint64_t value;
 
     if (host_memory_backend_mr_inited(backend)) {
-        error_setg(&local_err, "cannot change property value");
+        error_setg(&local_err, "cannot change property %s of %s ",
+                   name, object_get_typename(obj));
         goto out;
     }
 
@@ -66,8 +67,9 @@ host_memory_backend_set_size(Object *obj, Visitor *v, const char *name,
         goto out;
     }
     if (!value) {
-        error_setg(&local_err, "Property '%s.%s' doesn't take value '%"
-                   PRIu64 "'", object_get_typename(obj), name, value);
+        error_setg(&local_err,
+                   "property '%s' of %s doesn't take value '%" PRIu64 "'",
+                   name, object_get_typename(obj), value);
         goto out;
     }
     backend->size = value;