[Qemu-devel] [PATCH RFC v3 15/27] COLO failover: Implement COLO master/slave failover work

[zhanghailiang]

If failover is requested, after some cleanup work,
PVM or SVM will exit COLO mode, and resume to normal run.

Signed-off-by: zhanghailiang <address@hidden>
Signed-off-by: Li Zhijian <address@hidden>
Signed-off-by: Lai Jiangshan <address@hidden>
---
 include/migration/migration-colo.h     |  14 ++++
 include/migration/migration-failover.h |   2 +
 migration/colo-comm.c                  |  10 +++
 migration/colo-failover.c              |  12 +++-
 migration/colo.c                       | 122 ++++++++++++++++++++++++++++++++-
 stubs/migration-colo.c                 |   5 ++
 6 files changed, 163 insertions(+), 2 deletions(-)

diff --git a/include/migration/migration-colo.h 
b/include/migration/migration-colo.h
index 27a515a..3bdd1ae 100644
--- a/include/migration/migration-colo.h
+++ b/include/migration/migration-colo.h
@@ -21,6 +21,13 @@
 
 void colo_info_mig_init(void);
 
+/* Checkpoint control, called in migration/checkpoint thread */
+enum {
+    COLO_UNPROTECTED_MODE = 0,
+    COLO_PRIMARY_MODE,
+    COLO_SECONDARY_MODE,
+};
+
 struct colo_incoming {
     QEMUFile *file;
     QemuThread thread;
@@ -35,8 +42,15 @@ bool loadvm_enable_colo(void);
 void loadvm_exit_colo(void);
 void *colo_process_incoming_checkpoints(void *opaque);
 bool loadvm_in_colo_state(void);
+
+int get_colo_mode(void);
+
 /* ram cache */
 void create_and_init_ram_cache(void);
 void colo_flush_ram_cache(void);
 void release_ram_cache(void);
+
+/* failover */
+void colo_do_failover(MigrationState *s);
+
 #endif
diff --git a/include/migration/migration-failover.h 
b/include/migration/migration-failover.h
index 5fd376a..385fab3 100644
--- a/include/migration/migration-failover.h
+++ b/include/migration/migration-failover.h
@@ -16,5 +16,7 @@
 #include "qemu-common.h"
 
 void failover_request_set(void);
+void failover_request_clear(void);
+bool failover_request_is_set(void);
 
 #endif
diff --git a/migration/colo-comm.c b/migration/colo-comm.c
index 038d12f..57bc6cd 100644
--- a/migration/colo-comm.c
+++ b/migration/colo-comm.c
@@ -32,6 +32,16 @@ static void colo_info_save(QEMUFile *f, void *opaque)
 }
 
 /* restore */
+int get_colo_mode(void)
+{
+    if (migrate_in_colo_state()) {
+        return COLO_PRIMARY_MODE;
+    } else if (loadvm_in_colo_state()) {
+        return COLO_SECONDARY_MODE;
+    } else {
+        return COLO_UNPROTECTED_MODE;
+    }
+}
 static int colo_info_load(QEMUFile *f, void *opaque, int version_id)
 {
     int value = qemu_get_byte(f);
diff --git a/migration/colo-failover.c b/migration/colo-failover.c
index af78054..850b05c 100644
--- a/migration/colo-failover.c
+++ b/migration/colo-failover.c
@@ -22,7 +22,7 @@ static void colo_failover_bh(void *opaque)
 {
     qemu_bh_delete(failover_bh);
     failover_bh = NULL;
-    /*TODO: Do failover work */
+    colo_do_failover(NULL);
 }
 
 void failover_request_set(void)
@@ -32,6 +32,16 @@ void failover_request_set(void)
     qemu_bh_schedule(failover_bh);
 }
 
+void failover_request_clear(void)
+{
+    failover_request = false;
+}
+
+bool failover_request_is_set(void)
+{
+    return failover_request;
+}
+
 void qmp_colo_lost_heartbeat(Error **errp)
 {
     failover_request_set();
diff --git a/migration/colo.c b/migration/colo.c
index cd84e4d..bcde1ec 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -65,6 +65,68 @@ static Coroutine *colo;
 #define COLO_BUFFER_BASE_SIZE (1000*1000*4ULL)
 QEMUSizedBuffer *colo_buffer;
 
+static bool colo_runstate_is_stopped(void)
+{
+    return runstate_check(RUN_STATE_COLO) || !runstate_is_running();
+}
+
+/*
+ * there are two way to entry this function
+ * 1. From colo checkpoint incoming thread, in this case
+ * we should protect it by iothread lock
+ * 2. From user command, because hmp/qmp command
+ * was happened in main loop, iothread lock will cause a
+ * dead lock.
+ */
+static void slave_do_failover(void)
+{
+    DPRINTF("do_failover!\n");
+
+    colo = NULL;
+
+    if (!autostart) {
+        error_report("\"-S\" qemu option will be ignored in colo slave side");
+        /* recover runstate to normal migration finish state */
+        autostart = true;
+    }
+
+    /* On slave side, jump to incoming co */
+    if (migration_incoming_co) {
+        qemu_coroutine_enter(migration_incoming_co, NULL);
+    }
+}
+
+static void master_do_failover(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    if (!colo_runstate_is_stopped()) {
+        vm_stop_force_state(RUN_STATE_COLO);
+    }
+
+    if (s->state != MIG_STATE_ERROR) {
+        migrate_set_state(s, MIG_STATE_COLO, MIG_STATE_COMPLETED);
+    }
+
+    vm_start();
+}
+
+static bool failover_completed;
+void colo_do_failover(MigrationState *s)
+{
+    /* Make sure vm stopped while failover */
+    if (!colo_runstate_is_stopped()) {
+        vm_stop_force_state(RUN_STATE_COLO);
+    }
+
+    if (get_colo_mode() == COLO_SECONDARY_MODE) {
+        slave_do_failover();
+    } else {
+        master_do_failover();
+    }
+    failover_completed = true;
+}
+
 /* colo checkpoint control helper */
 static int colo_ctl_put(QEMUFile *f, uint64_t request)
 {
@@ -142,11 +204,23 @@ static int do_colo_transaction(MigrationState *s, 
QEMUFile *control)
         goto out;
     }
 
+    if (failover_request_is_set()) {
+        ret = -1;
+        goto out;
+    }
     /* suspend and save vm state to colo buffer */
     qemu_mutex_lock_iothread();
     vm_stop_force_state(RUN_STATE_COLO);
     qemu_mutex_unlock_iothread();
     DPRINTF("vm is stoped\n");
+    /*
+     * failover request bh could be called after
+     * vm_stop_force_state so we check failover_request_is_set() again.
+     */
+    if (failover_request_is_set()) {
+        ret = -1;
+        goto out;
+    }
 
     /* Disable block migration */
     s->params.blk = 0;
@@ -242,7 +316,18 @@ static void *colo_thread(void *opaque)
     }
 
 out:
-    migrate_set_state(s, MIG_STATE_COLO, MIG_STATE_COMPLETED);
+    fprintf(stderr, "colo: some error happens in colo_thread\n");
+    qemu_mutex_lock_iothread();
+    if (!failover_request_is_set()) {
+        error_report("master takeover from checkpoint channel");
+        failover_request_set();
+    }
+    qemu_mutex_unlock_iothread();
+
+    while (!failover_completed) {
+        ;
+    }
+    failover_request_clear();
 
     if (colo_buffer) {
         qsb_free(colo_buffer);
@@ -284,6 +369,11 @@ void colo_init_checkpointer(MigrationState *s)
     qemu_bh_schedule(colo_bh);
 }
 
+bool loadvm_in_colo_state(void)
+{
+    return colo != NULL;
+}
+
 /*
  * return:
  * 0: start a checkpoint
@@ -347,6 +437,10 @@ void *colo_process_incoming_checkpoints(void *opaque)
         if (slave_wait_new_checkpoint(f)) {
             break;
         }
+        if (failover_request_is_set()) {
+            error_report("failover request from heartbeat channel");
+            goto out;
+        }
 
         /* suspend guest */
         qemu_mutex_lock_iothread();
@@ -415,6 +509,32 @@ void *colo_process_incoming_checkpoints(void *opaque)
     }
 
 out:
+    fprintf(stderr, "Detect some error or get a failover request\n");
+    /* determine whether we need to failover */
+    if (!failover_request_is_set()) {
+        /*
+        * TODO: Here, maybe we should raise a qmp event to the user,
+        * It can help user to know what happens, and help deciding whether to
+        * do failover.
+        */
+        usleep(2000 * 1000);
+    }
+    /* check flag again*/
+    if (!failover_request_is_set()) {
+        /*
+        * We assume that master is still alive according to heartbeat,
+        * just kill slave
+        */
+        error_report("SVM is going to exit!");
+        exit(1);
+    } else {
+        /* if we went here, means master may dead, we are doing failover */
+        while (!failover_completed) {
+            ;
+        }
+        failover_request_clear();
+    }
+
     colo = NULL;
 
     if (fb) {
diff --git a/stubs/migration-colo.c b/stubs/migration-colo.c
index a690b04..c3514c8 100644
--- a/stubs/migration-colo.c
+++ b/stubs/migration-colo.c
@@ -27,6 +27,11 @@ bool migrate_in_colo_state(void)
     return false;
 }
 
+bool loadvm_in_colo_state(void)
+{
+    return false;
+}
+
 void qmp_colo_lost_heartbeat(Error **errp)
 {
     error_setg(errp, "COLO is not supported, please rerun configure"
-- 
1.7.12.4