migration: new cmd MIG_CMD_POSTCOPY_RESUME

Introducing this new command to be sent when the source VM is ready to
resume the paused migration.  What the destination does here is
basically release the fault thread to continue service page faults.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180502104740.12123-14-peterx@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

3 files changed, 38 insertions, 0 deletions

diff --git a/migration/savevm.c b/migration/savevm.c
index 7176b350d5..a7e793eef7 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -80,6 +80,7 @@ enum qemu_vm_cmd {
     MIG_CMD_POSTCOPY_RAM_DISCARD,  /* A list of pages to discard that
                                       were previously sent during
                                       precopy but are dirty. */
+    MIG_CMD_POSTCOPY_RESUME,       /* resume postcopy on dest */
     MIG_CMD_PACKAGED,          /* Send a wrapped stream within this stream */
     MIG_CMD_RECV_BITMAP,       /* Request for recved bitmap on dst */
     MIG_CMD_MAX
@@ -98,6 +99,7 @@ static struct mig_cmd_args {
     [MIG_CMD_POSTCOPY_RUN]     = { .len =  0, .name = "POSTCOPY_RUN" },
     [MIG_CMD_POSTCOPY_RAM_DISCARD] = {
                                    .len = -1, .name = "POSTCOPY_RAM_DISCARD" },
+    [MIG_CMD_POSTCOPY_RESUME]  = { .len =  0, .name = "POSTCOPY_RESUME" },
     [MIG_CMD_PACKAGED]         = { .len =  4, .name = "PACKAGED" },
     [MIG_CMD_RECV_BITMAP]      = { .len = -1, .name = "RECV_BITMAP" },
     [MIG_CMD_MAX]              = { .len = -1, .name = "MAX" },
@@ -958,6 +960,12 @@ void qemu_savevm_send_postcopy_run(QEMUFile *f)
     qemu_savevm_command_send(f, MIG_CMD_POSTCOPY_RUN, 0, NULL);
 }
 
+void qemu_savevm_send_postcopy_resume(QEMUFile *f)
+{
+    trace_savevm_send_postcopy_resume();
+    qemu_savevm_command_send(f, MIG_CMD_POSTCOPY_RESUME, 0, NULL);
+}
+
 void qemu_savevm_send_recv_bitmap(QEMUFile *f, char *block_name)
 {
     size_t len;
@@ -1768,6 +1776,30 @@ static int loadvm_postcopy_handle_run(MigrationIncomingState *mis)
     return LOADVM_QUIT;
 }
 
+static int loadvm_postcopy_handle_resume(MigrationIncomingState *mis)
+{
+    if (mis->state != MIGRATION_STATUS_POSTCOPY_RECOVER) {
+        error_report("%s: illegal resume received", __func__);
+        /* Don't fail the load, only for this. */
+        return 0;
+    }
+
+    /*
+     * This means source VM is ready to resume the postcopy migration.
+     * It's time to switch state and release the fault thread to
+     * continue service page faults.
+     */
+    migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_RECOVER,
+                      MIGRATION_STATUS_POSTCOPY_ACTIVE);
+    qemu_sem_post(&mis->postcopy_pause_sem_fault);
+
+    trace_loadvm_postcopy_handle_resume();
+
+    /* TODO: Tell source that "we are ready" */
+
+    return 0;
+}
+
 /**
  * Immediately following this command is a blob of data containing an embedded
  * chunk of migration stream; read it and load it.
@@ -1933,6 +1965,9 @@ static int loadvm_process_command(QEMUFile *f)
     case MIG_CMD_POSTCOPY_RAM_DISCARD:
         return loadvm_postcopy_ram_handle_discard(mis, len);
 
+    case MIG_CMD_POSTCOPY_RESUME:
+        return loadvm_postcopy_handle_resume(mis);
+
     case MIG_CMD_RECV_BITMAP:
         return loadvm_handle_recv_bitmap(mis, len);
     }
diff --git a/migration/savevm.h b/migration/savevm.h
index b8cee00d41..b24ff073ad 100644
--- a/migration/savevm.h
+++ b/migration/savevm.h
@@ -47,6 +47,7 @@ int qemu_savevm_send_packaged(QEMUFile *f, const uint8_t *buf, size_t len);
 void qemu_savevm_send_postcopy_advise(QEMUFile *f);
 void qemu_savevm_send_postcopy_listen(QEMUFile *f);
 void qemu_savevm_send_postcopy_run(QEMUFile *f);
+void qemu_savevm_send_postcopy_resume(QEMUFile *f);
 void qemu_savevm_send_recv_bitmap(QEMUFile *f, char *block_name);
 
 void qemu_savevm_send_postcopy_ram_discard(QEMUFile *f, const char *name,
diff --git a/migration/trace-events b/migration/trace-events
index 72e57089f3..29cc10f299 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -18,6 +18,7 @@ loadvm_postcopy_handle_listen(void) ""
 loadvm_postcopy_handle_run(void) ""
 loadvm_postcopy_handle_run_cpu_sync(void) ""
 loadvm_postcopy_handle_run_vmstart(void) ""
+loadvm_postcopy_handle_resume(void) ""
 loadvm_postcopy_ram_handle_discard(void) ""
 loadvm_postcopy_ram_handle_discard_end(void) ""
 loadvm_postcopy_ram_handle_discard_header(const char *ramid, uint16_t len) "%s: %ud"
@@ -35,6 +36,7 @@ savevm_send_open_return_path(void) ""
 savevm_send_ping(uint32_t val) "0x%x"
 savevm_send_postcopy_listen(void) ""
 savevm_send_postcopy_run(void) ""
+savevm_send_postcopy_resume(void) ""
 savevm_send_recv_bitmap(char *name) "%s"
 savevm_state_setup(void) ""
 savevm_state_header(void) ""