Re: [Qemu-devel] [PATCH 08/11] qjson: Simplify by using json-output-visitor

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/12/2015 00:53, Eric Blake wrote:
> Instead of rolling our own limited JSON outputter, we can just
> wrap the more full-featured JSON output Visitor.
> 
> This slightly changes the output (different spacing), but the
> result is still equivalent JSON contents.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>  qjson.c | 61 ++++++++++++++++++++++---------------------------------------
>  1 file changed, 22 insertions(+), 39 deletions(-)

I didn't find out which tree your patches apply to, but this:

diff --git a/migration/savevm.c b/migration/savevm.c
index 0ad1b93..26986d8 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -646,7 +646,7 @@ static int vmstate_load(QEMUFile *f, SaveStateEntry *se, int version_id)
     return vmstate_load_state(f, se->vmsd, se->opaque, version_id);
 }
 
-static void vmstate_save_old_style(QEMUFile *f, SaveStateEntry *se, QJSON *vmdesc)
+static void vmstate_save_old_style(QEMUFile *f, SaveStateEntry *se, Visitor *vmdesc)
 {
     int64_t old_offset, size;
 
@@ -655,14 +655,14 @@ static void vmstate_save_old_style(QEMUFile *f, SaveStateEntry *se, QJSON *vmdes
     size = qemu_ftell_fast(f) - old_offset;
 
     if (vmdesc) {
-        json_prop_int(vmdesc, "size", size);
-        json_start_array(vmdesc, "fields");
-        json_start_object(vmdesc, NULL);
-        json_prop_str(vmdesc, "name", "data");
-        json_prop_int(vmdesc, "size", size);
-        json_prop_str(vmdesc, "type", "buffer");
-        json_end_object(vmdesc);
-        json_end_array(vmdesc);
+        visit_type_int(vmdesc, size, "size", &error_abort);
+        visit_start_list(vmdesc, NULL, 0, "fields", &error_abort);
+        visit_start_struct(vmdesc, NULL, 0, NULL, &error_abort);
+        visit_type_str(vmdesc, (char **)&"data", "name", &error_abort);
+        visit_type_int(vmdesc, size, "size", &error_abort);
+        visit_type_str(vmdesc, (char **)&"buffer", "type", &error_abort);
+        visit_end_struct(vmdesc);
+        visit_end_list(vmdesc);
     }
 }
 
@@ -1028,7 +1028,9 @@ void qemu_savevm_state_complete_postcopy(QEMUFile *f)
 
 void qemu_savevm_state_complete_precopy(QEMUFile *f, bool iterable_only)
 {
-    QJSON *vmdesc;
+    JsonOutputVisitor *vmdesc_jov;
+    Visitor *vmdesc;
+    char *vmdesc_str;
     int vmdesc_len;
     SaveStateEntry *se;
     int ret;
@@ -1068,9 +1070,11 @@ void qemu_savevm_state_complete_precopy(QEMUFile *f, bool iterable_only)
         return;
     }
 
-    vmdesc = qjson_new();
-    json_prop_int(vmdesc, "page_size", TARGET_PAGE_SIZE);
-    json_start_array(vmdesc, "devices");
+    vmdesc_jov = json_output_visitor_new();
+    vmdesc = json_output_get_visitor(vmdesc_jov);
+    visit_start_struct(vmdesc, NULL, 0, NULL, &error_abort);
+    visit_type_int(vmdesc, TARGET_PAGE_SIZE, "page_size", &error_abort);
+    visit_start_list(vmdesc, NULL, 0, "devices", &error_abort);
     QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
 
         if ((!se->ops || !se->ops->save_state) && !se->vmsd) {
@@ -1083,15 +1087,15 @@ void qemu_savevm_state_complete_precopy(QEMUFile *f, bool iterable_only)
 
         trace_savevm_section_start(se->idstr, se->section_id);
 
-        json_start_object(vmdesc, NULL);
-        json_prop_str(vmdesc, "name", se->idstr);
-        json_prop_int(vmdesc, "instance_id", se->instance_id);
+        visit_start_struct(vmdesc, NULL, 0, NULL, &error_abort);
+        visit_type_str(vmdesc, (char **)&se->idstr, "name", &error_abort);
+        visit_type_int(vmdesc, se->instance_id, "instance_id", &error_abort);
 
         save_section_header(f, se, QEMU_VM_SECTION_FULL);
 
         vmstate_save(f, se, vmdesc);
 
-        json_end_object(vmdesc);
+        visit_end_struct(vmdesc);
         trace_savevm_section_end(se->idstr, se->section_id, 0);
         save_section_footer(f, se);
     }
@@ -1101,16 +1105,18 @@ void qemu_savevm_state_complete_precopy(QEMUFile *f, bool iterable_only)
         qemu_put_byte(f, QEMU_VM_EOF);
     }
 
-    json_end_array(vmdesc);
-    qjson_finish(vmdesc);
-    vmdesc_len = strlen(qjson_get_str(vmdesc));
+    visit_end_list(vmdesc);
+    visit_end_struct(vmdesc);
+    vmdesc_str = json_output_get_string(vmdesc_jov);
+    vmdesc_len = strlen(vmdesc_str);
 
     if (should_send_vmdesc()) {
         qemu_put_byte(f, QEMU_VM_VMDESCRIPTION);
         qemu_put_be32(f, vmdesc_len);
-        qemu_put_buffer(f, (uint8_t *)qjson_get_str(vmdesc), vmdesc_len);
+        qemu_put_buffer(f, (uint8_t *)vmdesc_str, vmdesc_len);
     }
-    object_unref(OBJECT(vmdesc));
+    g_free(vmdesc_str);
+    json_output_visitor_cleanup(vmdesc_jov);
 
     qemu_fflush(f);
 }

compiles and is pretty much a 1:1 translation from the qjson.c API to the
visitor API (using this patch as a guide).  Feel free to include it and
remove qjson.c.  Alternatively, you can leave out this patch and I'll test
and submit the transition.

Paolo