[Qemu-devel] [PATCH 01/18] migration: dump vmstate info as a json file for static analysis

[Amit Shah <amit.shah@redhat.com>]

This commit adds a new command, '-dump-vmstate', that takes a filename
as a parameter.  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.

This is based on a version from Andreas Färber posted here:
https://lists.gnu.org/archive/html/qemu-devel/2013-10/msg03095.html

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>
---
 include/migration/vmstate.h |   2 +
 qemu-options.hx             |   9 +++
 savevm.c                    | 134 ++++++++++++++++++++++++++++++++++++++++++++
 vl.c                        |  14 +++++
 4 files changed, 159 insertions(+)

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 7e45048..9829c0e 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -778,4 +778,6 @@ void vmstate_register_ram(struct MemoryRegion *memory, DeviceState *dev);
 void vmstate_unregister_ram(struct MemoryRegion *memory, DeviceState *dev);
 void vmstate_register_ram_global(struct MemoryRegion *memory);
 
+void dump_vmstate_json_to_file(FILE *out_fp);
+
 #endif
diff --git a/qemu-options.hx b/qemu-options.hx
index 781af14..d376227 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3146,6 +3146,15 @@ STEXI
 prepend a timestamp to each log message.(default:on)
 ETEXI
 
+DEF("dump-vmstate", HAS_ARG, QEMU_OPTION_dump_vmstate,
+    "-dump-vmstate <file>\n" "", 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
diff --git a/savevm.c b/savevm.c
index da8aa24..a4ce279 100644
--- a/savevm.c
+++ b/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"
@@ -241,6 +242,139 @@ 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 (!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;
diff --git a/vl.c b/vl.c
index 73e0661..165ec3e 100644
--- a/vl.c
+++ b/vl.c
@@ -2988,6 +2988,7 @@ int main(int argc, char **argv, char **envp)
     const char *trace_file = NULL;
     const ram_addr_t default_ram_size = (ram_addr_t)DEFAULT_RAM_SIZE *
                                         1024 * 1024;
+    FILE *vmstate_dump_file = NULL;
 
     atexit(qemu_run_exit_notifiers);
     error_set_progname(argv[0]);
@@ -3956,6 +3957,13 @@ 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);
             }
@@ -4533,6 +4541,12 @@ int main(int argc, char **argv, char **envp)
         }
     }
 
+    if (vmstate_dump_file) {
+        /* dump and exit */
+        dump_vmstate_json_to_file(vmstate_dump_file);
+        return 0;
+    }
+
     if (incoming) {
         Error *local_err = NULL;
         qemu_start_incoming_migration(incoming, &local_err);
-- 
1.9.0