migration: dump vmstate info as a json file for static analysis

This commit adds a new command, '-dump-vmstate', that takes a filename
as an argument.  When executed, QEMU will dump the vmstate information
for the machine type it's invoked with to the file, and quit.

The JSON-format output can then be used to compare the vmstate info for
different QEMU versions, specifically to test whether live migration
would break due to changes in the vmstate data.

A Python script that compares the output of such JSON dumps is included
in the following commit.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

include/migration/vmstate.h

@@ -788,4 +788,6 @@ int64_t self_announce_delay(int round)
     return 50 + (SELF_ANNOUNCE_ROUNDS - round - 1) * 100;
 }
 
+void dump_vmstate_json_to_file(FILE *out_fp);
+
 #endif

qemu-options.hx

@@ -3252,6 +3252,20 @@ STEXI
 prepend a timestamp to each log message.(default:on)
 ETEXI
 
+DEF("dump-vmstate", HAS_ARG, QEMU_OPTION_dump_vmstate,
+    "-dump-vmstate <file>\n"
+    "                Output vmstate information in JSON format to file.\n"
+    "                Use the scripts/vmstate-static-checker.py file to\n"
+    "                check for possible regressions in migration code\n"
+    "                by comparing two such vmstate dumps.",
+    QEMU_ARCH_ALL)
+STEXI
+@item -dump-vmstate @var{file}
+@findex -dump-vmstate
+Dump json-encoded vmstate information for current machine type to file
+in @var{file}
+ETEXI
+
 HXCOMM This is the last statement. Insert new options before this line!
 STEXI
 @end table

savevm.c

@@ -24,6 +24,7 @@
 
 #include "config-host.h"
 #include "qemu-common.h"
+#include "hw/boards.h"
 #include "hw/hw.h"
 #include "hw/qdev.h"
 #include "net/net.h"
@@ -240,6 +241,144 @@ static QTAILQ_HEAD(savevm_handlers, SaveStateEntry) savevm_handlers =
     QTAILQ_HEAD_INITIALIZER(savevm_handlers);
 static int global_section_id;
 
+static void dump_vmstate_vmsd(FILE *out_file,
+                              const VMStateDescription *vmsd, int indent,
+                              bool is_subsection);
+
+static void dump_vmstate_vmsf(FILE *out_file, const VMStateField *field,
+                              int indent)
+{
+    fprintf(out_file, "%*s{\n", indent, "");
+    indent += 2;
+    fprintf(out_file, "%*s\"field\": \"%s\",\n", indent, "", field->name);
+    fprintf(out_file, "%*s\"version_id\": %d,\n", indent, "",
+            field->version_id);
+    fprintf(out_file, "%*s\"field_exists\": %s,\n", indent, "",
+            field->field_exists ? "true" : "false");
+    fprintf(out_file, "%*s\"size\": %zu", indent, "", field->size);
+    if (field->vmsd != NULL) {
+        fprintf(out_file, ",\n");
+        dump_vmstate_vmsd(out_file, field->vmsd, indent, false);
+    }
+    fprintf(out_file, "\n%*s}", indent - 2, "");
+}
+
+static void dump_vmstate_vmss(FILE *out_file,
+                              const VMStateSubsection *subsection,
+                              int indent)
+{
+    if (subsection->vmsd != NULL) {
+        dump_vmstate_vmsd(out_file, subsection->vmsd, indent, true);
+    }
+}
+
+static void dump_vmstate_vmsd(FILE *out_file,
+                              const VMStateDescription *vmsd, int indent,
+                              bool is_subsection)
+{
+    if (is_subsection) {
+        fprintf(out_file, "%*s{\n", indent, "");
+    } else {
+        fprintf(out_file, "%*s\"%s\": {\n", indent, "", "Description");
+    }
+    indent += 2;
+    fprintf(out_file, "%*s\"name\": \"%s\",\n", indent, "", vmsd->name);
+    fprintf(out_file, "%*s\"version_id\": %d,\n", indent, "",
+            vmsd->version_id);
+    fprintf(out_file, "%*s\"minimum_version_id\": %d", indent, "",
+            vmsd->minimum_version_id);
+    if (vmsd->fields != NULL) {
+        const VMStateField *field = vmsd->fields;
+        bool first;
+
+        fprintf(out_file, ",\n%*s\"Fields\": [\n", indent, "");
+        first = true;
+        while (field->name != NULL) {
+            if (field->flags & VMS_MUST_EXIST) {
+                /* Ignore VMSTATE_VALIDATE bits; these don't get migrated */
+                field++;
+                continue;
+            }
+            if (!first) {
+                fprintf(out_file, ",\n");
+            }
+            dump_vmstate_vmsf(out_file, field, indent + 2);
+            field++;
+            first = false;
+        }
+        fprintf(out_file, "\n%*s]", indent, "");
+    }
+    if (vmsd->subsections != NULL) {
+        const VMStateSubsection *subsection = vmsd->subsections;
+        bool first;
+
+        fprintf(out_file, ",\n%*s\"Subsections\": [\n", indent, "");
+        first = true;
+        while (subsection->vmsd != NULL) {
+            if (!first) {
+                fprintf(out_file, ",\n");
+            }
+            dump_vmstate_vmss(out_file, subsection, indent + 2);
+            subsection++;
+            first = false;
+        }
+        fprintf(out_file, "\n%*s]", indent, "");
+    }
+    fprintf(out_file, "\n%*s}", indent - 2, "");
+}
+
+static void dump_machine_type(FILE *out_file)
+{
+    MachineClass *mc;
+
+    mc = MACHINE_GET_CLASS(current_machine);
+
+    fprintf(out_file, "  \"vmschkmachine\": {\n");
+    fprintf(out_file, "    \"Name\": \"%s\"\n", mc->name);
+    fprintf(out_file, "  },\n");
+}
+
+void dump_vmstate_json_to_file(FILE *out_file)
+{
+    GSList *list, *elt;
+    bool first;
+
+    fprintf(out_file, "{\n");
+    dump_machine_type(out_file);
+
+    first = true;
+    list = object_class_get_list(TYPE_DEVICE, true);
+    for (elt = list; elt; elt = elt->next) {
+        DeviceClass *dc = OBJECT_CLASS_CHECK(DeviceClass, elt->data,
+                                             TYPE_DEVICE);
+        const char *name;
+        int indent = 2;
+
+        if (!dc->vmsd) {
+            continue;
+        }
+
+        if (!first) {
+            fprintf(out_file, ",\n");
+        }
+        name = object_class_get_name(OBJECT_CLASS(dc));
+        fprintf(out_file, "%*s\"%s\": {\n", indent, "", name);
+        indent += 2;
+        fprintf(out_file, "%*s\"Name\": \"%s\",\n", indent, "", name);
+        fprintf(out_file, "%*s\"version_id\": %d,\n", indent, "",
+                dc->vmsd->version_id);
+        fprintf(out_file, "%*s\"minimum_version_id\": %d,\n", indent, "",
+                dc->vmsd->minimum_version_id);
+
+        dump_vmstate_vmsd(out_file, dc->vmsd, indent, false);
+
+        fprintf(out_file, "\n%*s}", indent - 2, "");
+        first = false;
+    }
+    fprintf(out_file, "\n}\n");
+    fclose(out_file);
+}
+
 static int calculate_new_instance_id(const char *idstr)
 {
     SaveStateEntry *se;

vl.c

@@ -2935,6 +2935,7 @@ int main(int argc, char **argv, char **envp)
                                         1024 * 1024;
     ram_addr_t maxram_size = default_ram_size;
     uint64_t ram_slots = 0;
+    FILE *vmstate_dump_file = NULL;
 
     atexit(qemu_run_exit_notifiers);
     error_set_progname(argv[0]);
@@ -3944,6 +3945,13 @@ int main(int argc, char **argv, char **envp)
                 }
                 configure_msg(opts);
                 break;
+            case QEMU_OPTION_dump_vmstate:
+                vmstate_dump_file = fopen(optarg, "w");
+                if (vmstate_dump_file == NULL) {
+                    fprintf(stderr, "open %s: %s\n", optarg, strerror(errno));
+                    exit(1);
+                }
+                break;
             default:
                 os_parse_cmd_args(popt->index, optarg);
             }
@@ -4495,6 +4503,11 @@ int main(int argc, char **argv, char **envp)
     }
 
     qdev_prop_check_global();
+    if (vmstate_dump_file) {
+        /* dump and exit */
+        dump_vmstate_json_to_file(vmstate_dump_file);
+        return 0;
+    }
 
     if (incoming) {
         Error *local_err = NULL;