Use error_is_set() only when necessary (again)

error_is_set(&var) is the same as var != NULL, but it takes
whole-program analysis to figure that out.  Unnecessarily hard for
optimizers, static checkers, and human readers.  Commit 84d18f0 dumbed
it down to obvious, but a few more have crept in since, and
documentation was overlooked.  Dumb these down, too.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block.c

@@ -864,7 +864,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
 
     node_name = qdict_get_try_str(options, "node-name");
     bdrv_assign_node_name(bs, node_name, &local_err);
-    if (error_is_set(&local_err)) {
+    if (local_err) {
         error_propagate(errp, local_err);
         return -EINVAL;
     }

block/mirror.c

@@ -680,7 +680,7 @@ void commit_active_start(BlockDriverState *bs, BlockDriverState *base,
     mirror_start_job(bs, base, speed, 0, 0,
                      on_error, on_error, cb, opaque, &local_err,
                      &commit_active_job_driver, false, base);
-    if (error_is_set(&local_err)) {
+    if (local_err) {
         error_propagate(errp, local_err);
         goto error_restore_flags;
     }

block/nfs.c

@@ -343,7 +343,7 @@ static int nfs_file_open(BlockDriverState *bs, QDict *options, int flags,
 
     opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
     qemu_opts_absorb_qdict(opts, options, &local_err);
-    if (error_is_set(&local_err)) {
+    if (local_err) {
         error_propagate(errp, local_err);
         return -EINVAL;
     }

block/quorum.c

@@ -753,7 +753,7 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
 
     opts = qemu_opts_create(&quorum_runtime_opts, NULL, 0, &error_abort);
     qemu_opts_absorb_qdict(opts, options, &local_err);
-    if (error_is_set(&local_err)) {
+    if (local_err) {
         ret = -EINVAL;
         goto exit;
     }
@@ -828,7 +828,7 @@ close_exit:
     g_free(opened);
 exit:
     /* propagate error */
-    if (error_is_set(&local_err)) {
+    if (local_err) {
         error_propagate(errp, local_err);
     }
     QDECREF(list);

docs/writing-qmp-commands.txt

@@ -311,7 +311,7 @@ void hmp_hello_world(Monitor *mon, const QDict *qdict)
     Error *errp = NULL;
 
     qmp_hello_world(!!message, message, &errp);
-    if (error_is_set(&errp)) {
+    if (errp) {
         monitor_printf(mon, "%s\n", error_get_pretty(errp));
         error_free(errp);
         return;
@@ -483,7 +483,7 @@ void hmp_info_alarm_clock(Monitor *mon)
     Error *errp = NULL;
 
     clock = qmp_query_alarm_clock(&errp);
-    if (error_is_set(&errp)) {
+    if (errp) {
         monitor_printf(mon, "Could not query alarm clock information\n");
         error_free(errp);
         return;
@@ -634,7 +634,7 @@ void hmp_info_alarm_methods(Monitor *mon)
     Error *errp = NULL;
 
     method_list = qmp_query_alarm_methods(&errp);
-    if (error_is_set(&errp)) {
+    if (errp) {
         monitor_printf(mon, "Could not query alarm methods\n");
         error_free(errp);
         return;

tests/test-qmp-input-strict.c

@@ -153,7 +153,7 @@ static void test_validate_union_flat(TestInputVisitorData *data,
     /* TODO when generator bug is fixed, add 'integer': 41 */
 
     visit_type_UserDefFlatUnion(v, &tmp, NULL, &errp);
-    g_assert(!error_is_set(&errp));
+    g_assert(!errp);
     qapi_free_UserDefFlatUnion(tmp);
 }
 
@@ -167,7 +167,7 @@ static void test_validate_union_anon(TestInputVisitorData *data,
     v = validate_test_init(data, "42");
 
     visit_type_UserDefAnonUnion(v, &tmp, NULL, &errp);
-    g_assert(!error_is_set(&errp));
+    g_assert(!errp);
     qapi_free_UserDefAnonUnion(tmp);
 }
 
@@ -240,7 +240,7 @@ static void test_validate_fail_union_flat(TestInputVisitorData *data,
     v = validate_test_init(data, "{ 'string': 'c', 'integer': 41, 'boolean': true }");
 
     visit_type_UserDefFlatUnion(v, &tmp, NULL, &errp);
-    g_assert(error_is_set(&errp));
+    g_assert(errp);
     qapi_free_UserDefFlatUnion(tmp);
 }
 
@@ -254,7 +254,7 @@ static void test_validate_fail_union_anon(TestInputVisitorData *data,
     v = validate_test_init(data, "3.14");
 
     visit_type_UserDefAnonUnion(v, &tmp, NULL, &errp);
-    g_assert(error_is_set(&errp));
+    g_assert(errp);
     qapi_free_UserDefAnonUnion(tmp);
 }