[v8,19/54] Return path: Control commands

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 0bb4383..98a6d07 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -48,6 +48,8 @@  typedef QLIST_HEAD(, LoadStateEntry) LoadStateEntry_Head;
 struct MigrationIncomingState {
     QEMUFile *from_src_file;
 
+    QEMUFile *to_src_file;
+
     /* See savevm.c */
     LoadStateEntry_Head loadvm_handlers;
 };
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 07e9502..c6a3a78 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -87,6 +87,8 @@  void qemu_announce_self(void);
 /* Subcommands for QEMU_VM_COMMAND */
 enum qemu_vm_cmd {
     MIG_CMD_INVALID = 0,   /* Must be 0 */
+    MIG_CMD_OPEN_RETURN_PATH,  /* Tell the dest to open the Return path */
+    MIG_CMD_PING,              /* Request a PONG on the RP */
     MIG_CMD_MAX
 };
 
@@ -100,6 +102,8 @@  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);
+void qemu_savevm_send_ping(QEMUFile *f, uint32_t value);
+void qemu_savevm_send_open_return_path(QEMUFile *f);
 int qemu_loadvm_state(QEMUFile *f);
 
 typedef enum DisplayType
diff --git a/migration/savevm.c b/migration/savevm.c
index eb495e6..819ab1e 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -64,6 +64,8 @@  static struct mig_cmd_args {
     const char *name;
 } mig_cmd_args[] = {
     [MIG_CMD_INVALID]          = { .len = -1, .name = "INVALID" },
+    [MIG_CMD_OPEN_RETURN_PATH] = { .len =  0, .name = "OPEN_RETURN_PATH" },
+    [MIG_CMD_PING]             = { .len = sizeof(uint32_t), .name = "PING" },
     [MIG_CMD_MAX]              = { .len = -1, .name = "MAX" },
 };
 
@@ -723,6 +725,20 @@  void qemu_savevm_command_send(QEMUFile *f,
     qemu_fflush(f);
 }
 
+void qemu_savevm_send_ping(QEMUFile *f, uint32_t value)
+{
+    uint32_t buf;
+
+    trace_savevm_send_ping(value);
+    buf = cpu_to_be32(value);
+    qemu_savevm_command_send(f, MIG_CMD_PING, sizeof(value), (uint8_t *)&buf);
+}
+
+void qemu_savevm_send_open_return_path(QEMUFile *f)
+{
+    qemu_savevm_command_send(f, MIG_CMD_OPEN_RETURN_PATH, 0, NULL);
+}
+
 bool qemu_savevm_state_blocked(Error **errp)
 {
     SaveStateEntry *se;
@@ -1042,8 +1058,10 @@  static SaveStateEntry *find_se(const char *idstr, int instance_id)
  */
 static int loadvm_process_command(QEMUFile *f)
 {
+    MigrationIncomingState *mis = migration_incoming_get_current();
     uint16_t cmd;
     uint16_t len;
+    uint32_t tmp32;
 
     cmd = qemu_get_be16(f);
     len = qemu_get_be16(f);
@@ -1061,7 +1079,29 @@  static int loadvm_process_command(QEMUFile *f)
     }
 
     switch (cmd) {
-        /* Filling added in next patch */
+    case MIG_CMD_OPEN_RETURN_PATH:
+        if (mis->to_src_file) {
+            error_report("CMD_OPEN_RETURN_PATH called when RP already open");
+            /* Not really a problem, so don't give up */
+            return 0;
+        }
+        mis->to_src_file = qemu_file_get_return_path(f);
+        if (!mis->to_src_file) {
+            error_report("CMD_OPEN_RETURN_PATH failed");
+            return -1;
+        }
+        break;
+
+    case MIG_CMD_PING:
+        tmp32 = qemu_get_be32(f);
+        trace_loadvm_process_command_ping(tmp32);
+        if (!mis->to_src_file) {
+            error_report("CMD_PING (0x%x) received with no return path",
+                         tmp32);
+            return -1;
+        }
+        /* migrate_send_rp_pong(mis, tmp32); TODO: gets added later */
+        break;
     }
 
     return 0;
diff --git a/trace-events b/trace-events
index b6cdf11..4d4e9dc 100644
--- a/trace-events
+++ b/trace-events
@@ -1198,10 +1198,12 @@  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"
+loadvm_process_command_ping(uint32_t val) "%x"
 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"
+savevm_send_ping(uint32_t val) "%x"
 savevm_state_begin(void) ""
 savevm_state_header(void) ""
 savevm_state_iterate(void) ""