[Qemu-devel] [PATCH 3/4] qom: Clean up fragile use of error_is_set() in set() methods

[Markus Armbruster]

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 <address@hidden>
---
 backends/rng.c             | 11 +++++++----
 backends/tpm.c             | 11 +++++++----
 hw/core/qdev-properties.c  | 11 +++++++----
 hw/misc/tmp105.c           |  6 ++++--
 hw/virtio/virtio-balloon.c |  6 ++++--
 target-i386/cpu.c          | 24 ++++++++++++++++--------
 6 files changed, 45 insertions(+), 24 deletions(-)

diff --git a/backends/rng.c b/backends/rng.c
index 8b8d5a4..0f2fc11 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 b735801..01860c4 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 c67acf5..5c08611 100644
--- a/hw/core/qdev-properties.c
+++ b/hw/core/qdev-properties.c
@@ -746,6 +746,7 @@ static void set_prop_arraylen(Object *obj, Visitor *v, void 
*opaque,
      * array-length field in the device struct, we have to create the
      * array itself and dynamically add the corresponding properties.
      */
+    Error *local_err = NULL;
     DeviceState *dev = DEVICE(obj);
     Property *prop = opaque;
     uint32_t *alenptr = qdev_get_prop_ptr(dev, prop);
@@ -763,8 +764,9 @@ 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) {
@@ -801,8 +803,9 @@ 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 63aa3d6..e11657d 100644
--- a/hw/misc/tmp105.c
+++ b/hw/misc/tmp105.c
@@ -67,11 +67,13 @@ static void tmp105_get_temperature(Object *obj, Visitor *v, 
void *opaque,
 static void tmp105_set_temperature(Object *obj, Visitor *v, void *opaque,
                                    const char *name, Error **errp)
 {
+    Error *local_err = NULL;
     TMP105State *s = TMP105(obj);
     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 a470a0b..51f02eb 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -141,11 +141,13 @@ static void balloon_stats_set_poll_interval(Object *obj, 
struct Visitor *v,
                                             void *opaque, const char *name,
                                             Error **errp)
 {
+    Error *local_err = NULL;
     VirtIOBalloon *s = opaque;
     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 8fd1497..73954a7 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -1296,14 +1296,16 @@ static void x86_cpuid_version_get_family(Object *obj, 
Visitor *v, void *opaque,
 static void x86_cpuid_version_set_family(Object *obj, Visitor *v, void *opaque,
                                          const char *name, Error **errp)
 {
+    Error *local_err = NULL;
     X86CPU *cpu = X86_CPU(obj);
     CPUX86State *env = &cpu->env;
     const int64_t min = 0;
     const int64_t max = 0xff + 0xf;
     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) {
@@ -1335,14 +1337,16 @@ static void x86_cpuid_version_get_model(Object *obj, 
Visitor *v, void *opaque,
 static void x86_cpuid_version_set_model(Object *obj, Visitor *v, void *opaque,
                                         const char *name, Error **errp)
 {
+    Error *local_err = NULL;
     X86CPU *cpu = X86_CPU(obj);
     CPUX86State *env = &cpu->env;
     const int64_t min = 0;
     const int64_t max = 0xff;
     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) {
@@ -1371,14 +1375,16 @@ static void x86_cpuid_version_set_stepping(Object *obj, 
Visitor *v,
                                            void *opaque, const char *name,
                                            Error **errp)
 {
+    Error *local_err = NULL;
     X86CPU *cpu = X86_CPU(obj);
     CPUX86State *env = &cpu->env;
     const int64_t min = 0;
     const int64_t max = 0xf;
     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) {
@@ -1508,13 +1514,15 @@ static void x86_cpuid_get_tsc_freq(Object *obj, Visitor 
*v, void *opaque,
 static void x86_cpuid_set_tsc_freq(Object *obj, Visitor *v, void *opaque,
                                    const char *name, Error **errp)
 {
+    Error *local_err = NULL;
     X86CPU *cpu = X86_CPU(obj);
     const int64_t min = 0;
     const int64_t max = INT64_MAX;
     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) {
-- 
1.8.1.4