qom: Clean up fragile use of error_is_set() in set() methods

Using error_is_set(ERRP) to find out whether a function failed is
either wrong, fragile, or unnecessarily opaque.  It's wrong when ERRP
may be null, because errors go undetected when it is.  It's fragile
when proving ERRP non-null involves a non-local argument.  Else, it's
unnecessarily opaque (see commit 84d18f0).

I guess the error_is_set(errp) in the ObjectProperty set() methods are
merely fragile right now, because I can't find a call chain that
passes a null errp argument.

Make the code more robust and more obviously correct: receive the
error in a local variable, then propagate it through the parameter.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>

6 files changed, 45 insertions, 24 deletions

diff --git a/backends/rng.c b/backends/rng.c
index 8b8d5a4973..0f2fc11dd8 100644
--- a/backends/rng.c
+++ b/backends/rng.c
@@ -50,6 +50,7 @@ static void rng_backend_prop_set_opened(Object *obj, bool value, Error **errp)
 {
     RngBackend *s = RNG_BACKEND(obj);
     RngBackendClass *k = RNG_BACKEND_GET_CLASS(s);
+    Error *local_err = NULL;
 
     if (value == s->opened) {
         return;
@@ -61,12 +62,14 @@ static void rng_backend_prop_set_opened(Object *obj, bool value, Error **errp)
     }
 
     if (k->opened) {
-        k->opened(s, errp);
+        k->opened(s, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            return;
+        }
     }
 
-    if (!error_is_set(errp)) {
-        s->opened = value;
-    }
+    s->opened = true;
 }
 
 static void rng_backend_init(Object *obj)
diff --git a/backends/tpm.c b/backends/tpm.c
index b73580134c..01860c4acb 100644
--- a/backends/tpm.c
+++ b/backends/tpm.c
@@ -112,6 +112,7 @@ static void tpm_backend_prop_set_opened(Object *obj, bool value, Error **errp)
 {
     TPMBackend *s = TPM_BACKEND(obj);
     TPMBackendClass *k = TPM_BACKEND_GET_CLASS(s);
+    Error *local_err = NULL;
 
     if (value == s->opened) {
         return;
@@ -123,12 +124,14 @@ static void tpm_backend_prop_set_opened(Object *obj, bool value, Error **errp)
     }
 
     if (k->opened) {
-        k->opened(s, errp);
+        k->opened(s, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            return;
+        }
     }
 
-    if (!error_is_set(errp)) {
-        s->opened = value;
-    }
+    s->opened = true;
 }
 
 static void tpm_backend_instance_init(Object *obj)
diff --git a/hw/core/qdev-properties.c b/hw/core/qdev-properties.c
index 585a8e902e..d8cb5408c3 100644
--- a/hw/core/qdev-properties.c
+++ b/hw/core/qdev-properties.c
@@ -751,6 +751,7 @@ static void set_prop_arraylen(Object *obj, Visitor *v, void *opaque,
     Property *prop = opaque;
     uint32_t *alenptr = qdev_get_prop_ptr(dev, prop);
     void **arrayptr = (void *)dev + prop->arrayoffset;
+    Error *local_err = NULL;
     void *eltptr;
     const char *arrayname;
     int i;
@@ -764,8 +765,9 @@ static void set_prop_arraylen(Object *obj, Visitor *v, void *opaque,
                    name);
         return;
     }
-    visit_type_uint32(v, alenptr, name, errp);
-    if (error_is_set(errp)) {
+    visit_type_uint32(v, alenptr, name, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
         return;
     }
     if (!*alenptr) {
@@ -802,8 +804,9 @@ static void set_prop_arraylen(Object *obj, Visitor *v, void *opaque,
                             arrayprop->prop.info->get,
                             arrayprop->prop.info->set,
                             array_element_release,
-                            arrayprop, errp);
-        if (error_is_set(errp)) {
+                            arrayprop, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
             return;
         }
     }
diff --git a/hw/misc/tmp105.c b/hw/misc/tmp105.c
index 63aa3d6277..636ee97b16 100644
--- a/hw/misc/tmp105.c
+++ b/hw/misc/tmp105.c
@@ -68,10 +68,12 @@ static void tmp105_set_temperature(Object *obj, Visitor *v, void *opaque,
                                    const char *name, Error **errp)
 {
     TMP105State *s = TMP105(obj);
+    Error *local_err = NULL;
     int64_t temp;
 
-    visit_type_int(v, &temp, name, errp);
-    if (error_is_set(errp)) {
+    visit_type_int(v, &temp, name, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
         return;
     }
     if (temp >= 128000 || temp < -128000) {
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index a470a0b3a6..971a921777 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -142,10 +142,12 @@ static void balloon_stats_set_poll_interval(Object *obj, struct Visitor *v,
                                             Error **errp)
 {
     VirtIOBalloon *s = opaque;
+    Error *local_err = NULL;
     int64_t value;
 
-    visit_type_int(v, &value, name, errp);
-    if (error_is_set(errp)) {
+    visit_type_int(v, &value, name, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
         return;
     }
 
diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 8fd1497dc4..8f193a9330 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -1300,10 +1300,12 @@ static void x86_cpuid_version_set_family(Object *obj, Visitor *v, void *opaque,
     CPUX86State *env = &cpu->env;
     const int64_t min = 0;
     const int64_t max = 0xff + 0xf;
+    Error *local_err = NULL;
     int64_t value;
 
-    visit_type_int(v, &value, name, errp);
-    if (error_is_set(errp)) {
+    visit_type_int(v, &value, name, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
         return;
     }
     if (value < min || value > max) {
@@ -1339,10 +1341,12 @@ static void x86_cpuid_version_set_model(Object *obj, Visitor *v, void *opaque,
     CPUX86State *env = &cpu->env;
     const int64_t min = 0;
     const int64_t max = 0xff;
+    Error *local_err = NULL;
     int64_t value;
 
-    visit_type_int(v, &value, name, errp);
-    if (error_is_set(errp)) {
+    visit_type_int(v, &value, name, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
         return;
     }
     if (value < min || value > max) {
@@ -1375,10 +1379,12 @@ static void x86_cpuid_version_set_stepping(Object *obj, Visitor *v,
     CPUX86State *env = &cpu->env;
     const int64_t min = 0;
     const int64_t max = 0xf;
+    Error *local_err = NULL;
     int64_t value;
 
-    visit_type_int(v, &value, name, errp);
-    if (error_is_set(errp)) {
+    visit_type_int(v, &value, name, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
         return;
     }
     if (value < min || value > max) {
@@ -1511,10 +1517,12 @@ static void x86_cpuid_set_tsc_freq(Object *obj, Visitor *v, void *opaque,
     X86CPU *cpu = X86_CPU(obj);
     const int64_t min = 0;
     const int64_t max = INT64_MAX;
+    Error *local_err = NULL;
     int64_t value;
 
-    visit_type_int(v, &value, name, errp);
-    if (error_is_set(errp)) {
+    visit_type_int(v, &value, name, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
         return;
     }
     if (value < min || value > max) {