[v8,18/54] Migration commands

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 82cc3a6..0bb4383 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -35,6 +35,7 @@ 
 #define QEMU_VM_SUBSECTION           0x05
 #define QEMU_VM_VMDESCRIPTION        0x06
 #define QEMU_VM_CONFIGURATION        0x07
+#define QEMU_VM_COMMAND              0x08
 #define QEMU_VM_SECTION_FOOTER       0x7e
 
 struct MigrationParams {
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 7fd6c73..07e9502 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -84,6 +84,12 @@  void hmp_info_snapshots(Monitor *mon, const QDict *qdict);
 
 void qemu_announce_self(void);
 
+/* Subcommands for QEMU_VM_COMMAND */
+enum qemu_vm_cmd {
+    MIG_CMD_INVALID = 0,   /* Must be 0 */
+    MIG_CMD_MAX
+};
+
 bool qemu_savevm_state_blocked(Error **errp);
 void qemu_savevm_state_begin(QEMUFile *f,
                              const MigrationParams *params);
@@ -92,6 +98,8 @@  int qemu_savevm_state_iterate(QEMUFile *f);
 void qemu_savevm_state_complete_precopy(QEMUFile *f);
 void qemu_savevm_state_cancel(void);
 uint64_t qemu_savevm_state_pending(QEMUFile *f, uint64_t max_size);
+void qemu_savevm_command_send(QEMUFile *f, enum qemu_vm_cmd command,
+                              uint16_t len, uint8_t *data);
 int qemu_loadvm_state(QEMUFile *f);
 
 typedef enum DisplayType
diff --git a/migration/savevm.c b/migration/savevm.c
index e621afd..eb495e6 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -59,6 +59,14 @@ 
 
 static bool skip_section_footers;
 
+static struct mig_cmd_args {
+    ssize_t     len; /* -1 = variable */
+    const char *name;
+} mig_cmd_args[] = {
+    [MIG_CMD_INVALID]          = { .len = -1, .name = "INVALID" },
+    [MIG_CMD_MAX]              = { .len = -1, .name = "MAX" },
+};
+
 static int announce_self_create(uint8_t *buf,
                                 uint8_t *mac_addr)
 {
@@ -693,6 +701,28 @@  static void save_section_footer(QEMUFile *f, SaveStateEntry *se)
     }
 }
 
+/**
+ * qemu_savevm_command_send: Send a 'QEMU_VM_COMMAND' type element with the
+ *                           command and associated data.
+ *
+ * @f: File to send command on
+ * @command: Command type to send
+ * @len: Length of associated data
+ * @data: Data associated with command.
+ */
+void qemu_savevm_command_send(QEMUFile *f,
+                              enum qemu_vm_cmd command,
+                              uint16_t len,
+                              uint8_t *data)
+{
+    trace_savevm_command_send(command, len);
+    qemu_put_byte(f, QEMU_VM_COMMAND);
+    qemu_put_be16(f, (uint16_t)command);
+    qemu_put_be16(f, len);
+    qemu_put_buffer(f, data, len);
+    qemu_fflush(f);
+}
+
 bool qemu_savevm_state_blocked(Error **errp)
 {
     SaveStateEntry *se;
@@ -1003,6 +1033,40 @@  static SaveStateEntry *find_se(const char *idstr, int instance_id)
     return NULL;
 }
 
+/**
+ * loadvm_process_command: Process an incoming 'QEMU_VM_COMMAND'
+ *
+ * Returns: 0 on success, negative on error (in which case it will issue an
+ *          error message).
+ * @f: The stream to read the command data from.
+ */
+static int loadvm_process_command(QEMUFile *f)
+{
+    uint16_t cmd;
+    uint16_t len;
+
+    cmd = qemu_get_be16(f);
+    len = qemu_get_be16(f);
+
+    trace_loadvm_process_command(cmd, len);
+    if (cmd >= MIG_CMD_MAX || cmd == MIG_CMD_INVALID) {
+        error_report("MIG_CMD 0x%x unknown (len 0x%x)", cmd, len);
+        return -EINVAL;
+    }
+
+    if (mig_cmd_args[cmd].len != -1 && mig_cmd_args[cmd].len != len) {
+        error_report("%s received with bad length - expecting %zd, got %d",
+                      mig_cmd_args[cmd].name, mig_cmd_args[cmd].len, len);
+        return -ERANGE;
+    }
+
+    switch (cmd) {
+        /* Filling added in next patch */
+    }
+
+    return 0;
+}
+
 struct LoadStateEntry {
     QLIST_ENTRY(LoadStateEntry) entry;
     SaveStateEntry *se;
@@ -1182,6 +1246,12 @@  int qemu_loadvm_state(QEMUFile *f)
                 goto out;
             }
             break;
+        case QEMU_VM_COMMAND:
+            ret = loadvm_process_command(f);
+            if (ret < 0) {
+                goto out;
+            }
+            break;
         default:
             error_report("Unknown savevm section type %d", section_type);
             ret = -EINVAL;
diff --git a/trace-events b/trace-events
index cec51f6..b6cdf11 100644
--- a/trace-events
+++ b/trace-events
@@ -1197,6 +1197,8 @@  virtio_gpu_fence_resp(uint64_t fence) "fence 0x%" PRIx64
 qemu_loadvm_state_section(unsigned int section_type) "%d"
 qemu_loadvm_state_section_partend(uint32_t section_id) "%u"
 qemu_loadvm_state_section_startfull(uint32_t section_id, const char *idstr, uint32_t instance_id, uint32_t version_id) "%u(%s) %u %u"
+loadvm_process_command(uint16_t com, uint16_t len) "com=0x%x len=%d"
+savevm_command_send(uint16_t command, uint16_t len) "com=0x%x len=%d"
 savevm_section_start(const char *id, unsigned int section_id) "%s, section_id %u"
 savevm_section_end(const char *id, unsigned int section_id, int ret) "%s, section_id %u -> %d"
 savevm_section_skip(const char *id, unsigned int section_id) "%s, section_id %u"