[Qemu-devel] [PATCH v5 11/45] Return path: Send responses from destination to source

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Add migrate_send_rp_message to send a message from destination to source along the return path.
  (It uses a mutex to let it be called from multiple threads)
Add migrate_send_rp_shut to send a 'shut' message to indicate
  the destination is finished with the RP.
Add migrate_send_rp_ack to send a 'PONG' message in response to a PING
  Use it in the CMD_PING handler

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 include/migration/migration.h | 17 ++++++++++++++++
 migration/migration.c         | 45 +++++++++++++++++++++++++++++++++++++++++++
 savevm.c                      |  2 +-
 trace-events                  |  1 +
 4 files changed, 64 insertions(+), 1 deletion(-)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index c514dd4..6775747 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -41,6 +41,13 @@ struct MigrationParams {
     bool shared;
 };
 
+/* Commands sent on the return path from destination to source*/
+enum mig_rpcomm_cmd {
+    MIG_RP_CMD_INVALID = 0,  /* Must be 0 */
+    MIG_RP_CMD_SHUT,         /* sibling will not send any more RP messages */
+    MIG_RP_CMD_PONG,         /* Response to a PING; data (seq: be32 ) */
+};
+
 typedef struct MigrationState MigrationState;
 
 /* State for the incoming migration */
@@ -48,6 +55,7 @@ struct MigrationIncomingState {
     QEMUFile *file;
 
     QEMUFile *return_path;
+    QemuMutex      rp_mutex;    /* We send replies from multiple threads */
 };
 
 MigrationIncomingState *migration_incoming_get_current(void);
@@ -169,6 +177,15 @@ int64_t migrate_xbzrle_cache_size(void);
 
 int64_t xbzrle_cache_resize(int64_t new_size);
 
+/* Sending on the return path - generic and then for each message type */
+void migrate_send_rp_message(MigrationIncomingState *mis,
+                             enum mig_rpcomm_cmd cmd,
+                             uint16_t len, uint8_t *data);
+void migrate_send_rp_shut(MigrationIncomingState *mis,
+                          uint32_t value);
+void migrate_send_rp_pong(MigrationIncomingState *mis,
+                          uint32_t value);
+
 void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
 void ram_control_after_iterate(QEMUFile *f, uint64_t flags);
 void ram_control_load_hook(QEMUFile *f, uint64_t flags);
diff --git a/migration/migration.c b/migration/migration.c
index a36ea65..80d234c 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -78,6 +78,7 @@ MigrationIncomingState *migration_incoming_state_new(QEMUFile* f)
 {
     mis_current = g_malloc0(sizeof(MigrationIncomingState));
     mis_current->file = f;
+    qemu_mutex_init(&mis_current->rp_mutex);
 
     return mis_current;
 }
@@ -88,6 +89,50 @@ void migration_incoming_state_destroy(void)
     mis_current = NULL;
 }
 
+/*
+ * Send a message on the return channel back to the source
+ * of the migration.
+ */
+void migrate_send_rp_message(MigrationIncomingState *mis,
+                             enum mig_rpcomm_cmd cmd,
+                             uint16_t len, uint8_t *data)
+{
+    trace_migrate_send_rp_message((int)cmd, len);
+    qemu_mutex_lock(&mis->rp_mutex);
+    qemu_put_be16(mis->return_path, (unsigned int)cmd);
+    qemu_put_be16(mis->return_path, len);
+    qemu_put_buffer(mis->return_path, data, len);
+    qemu_fflush(mis->return_path);
+    qemu_mutex_unlock(&mis->rp_mutex);
+}
+
+/*
+ * Send a 'SHUT' message on the return channel with the given value
+ * to indicate that we've finished with the RP.  None-0 value indicates
+ * error.
+ */
+void migrate_send_rp_shut(MigrationIncomingState *mis,
+                          uint32_t value)
+{
+    uint32_t buf;
+
+    buf = cpu_to_be32(value);
+    migrate_send_rp_message(mis, MIG_RP_CMD_SHUT, 4, (uint8_t *)&buf);
+}
+
+/*
+ * Send a 'PONG' message on the return channel with the given value
+ * (normally in response to a 'PING')
+ */
+void migrate_send_rp_pong(MigrationIncomingState *mis,
+                          uint32_t value)
+{
+    uint32_t buf;
+
+    buf = cpu_to_be32(value);
+    migrate_send_rp_message(mis, MIG_RP_CMD_PONG, 4, (uint8_t *)&buf);
+}
+
 void qemu_start_incoming_migration(const char *uri, Error **errp)
 {
     const char *p;
diff --git a/savevm.c b/savevm.c
index d082738..7084d07 100644
--- a/savevm.c
+++ b/savevm.c
@@ -1008,7 +1008,7 @@ static int loadvm_process_command(QEMUFile *f)
                          tmp32);
             return -1;
         }
-        /* migrate_send_rp_pong(mis, tmp32); TODO: gets added later */
+        migrate_send_rp_pong(mis, tmp32);
         break;
 
     default:
diff --git a/trace-events b/trace-events
index 99e00b5..4f3eff8 100644
--- a/trace-events
+++ b/trace-events
@@ -1379,6 +1379,7 @@ migrate_fd_cleanup(void) ""
 migrate_fd_error(void) ""
 migrate_fd_cancel(void) ""
 migrate_pending(uint64_t size, uint64_t max) "pending size %" PRIu64 " max %" PRIu64
+migrate_send_rp_message(int cmd, uint16_t len) "cmd=%d, len=%d"
 migrate_transferred(uint64_t tranferred, uint64_t time_spent, double bandwidth, uint64_t size) "transferred %" PRIu64 " time_spent %" PRIu64 " bandwidth %g max_size %" PRId64
 
 # migration/rdma.c
-- 
2.1.0