[Qemu-devel] [PATCH COLO-Frame v11 10/39] COLO: Implement colo checkpoint protocol

[zhanghailiang]

We need communications protocol of user-defined to control the checkpoint
process.

The new checkpoint request is started by Primary VM, and the interactive process
like below:
Checkpoint synchronizing points,

                       Primary                         Secondary
                                                       initial work
'checkpoint-ready'     <------------------------------ @

'checkpoint-request'   @ ----------------------------->
                                                       Suspend (Only in hybrid 
mode)
'checkpoint-reply'     <------------------------------ @
                       Suspend&Save state
'vmstate-send'         @ ----------------------------->
                       Send state                      Receive state
'vmstate-received'     <------------------------------ @
                       Release packets                 Load state
'vmstate-load'         <------------------------------ @
                       Resume                          Resume (Only in hybrid 
mode)

                       Start Comparing (Only in hybrid mode)
NOTE:
 1) '@' who sends the message
 2) Every sync-point is synchronized by two sides with only
    one handshake(single direction) for low-latency.
    If more strict synchronization is required, a opposite direction
    sync-point should be added.
 3) Since sync-points are single direction, the remote side may
    go forward a lot when this side just receives the sync-point.
 4) For now, we only support 'periodic' checkpoint, for which
   the Secondary VM is not running, later we will support 'hybrid' mode.

Signed-off-by: zhanghailiang <address@hidden>
Signed-off-by: Li Zhijian <address@hidden>
Signed-off-by: Gonglei <address@hidden>
Cc: Eric Blake <address@hidden>
---
v11:
- Add missing 'checkpoint-ready' communication in comment.
- Use parameter to return 'value' for colo_ctl_get() (Dave's suggestion)
- Fix trace for colo_ctl_get() to trace command and value both
v10:
- Rename enum COLOCmd to COLOCommand (Eric's suggestion).
- Remove unused 'ram-steal'
---
 migration/colo.c | 198 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 qapi-schema.json |  27 ++++++++
 trace-events     |   2 +
 3 files changed, 225 insertions(+), 2 deletions(-)

diff --git a/migration/colo.c b/migration/colo.c
index 0ab9618..c045d61 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -10,10 +10,12 @@
  * later.  See the COPYING file in the top-level directory.
  */
 
+#include <unistd.h>
 #include "sysemu/sysemu.h"
 #include "migration/colo.h"
 #include "trace.h"
 #include "qemu/error-report.h"
+#include "qemu/sockets.h"
 
 bool colo_supported(void)
 {
@@ -34,9 +36,107 @@ bool migration_incoming_in_colo_state(void)
     return mis && (mis->state == MIGRATION_STATUS_COLO);
 }
 
+/* colo checkpoint control helper */
+static int colo_ctl_put(QEMUFile *f, uint32_t cmd, uint64_t value)
+{
+    int ret = 0;
+
+    qemu_put_be32(f, cmd);
+    qemu_put_be64(f, value);
+    qemu_fflush(f);
+
+    ret = qemu_file_get_error(f);
+    trace_colo_ctl_put(COLOCommand_lookup[cmd], value);
+
+    return ret;
+}
+
+static int colo_ctl_get_cmd(QEMUFile *f, uint32_t *cmd)
+{
+    int ret = 0;
+
+    *cmd = qemu_get_be32(f);
+    ret = qemu_file_get_error(f);
+    if (ret < 0) {
+        return ret;
+    }
+    if (*cmd >= COLO_COMMAND_MAX) {
+        error_report("Invalid colo command, got cmd:%d", *cmd);
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
+static int colo_ctl_get(QEMUFile *f, uint32_t require, uint64_t *value)
+{
+    int ret;
+    uint32_t cmd;
+
+    ret = colo_ctl_get_cmd(f, &cmd);
+    if (ret < 0) {
+        return ret;
+    }
+    if (cmd != require) {
+        error_report("Unexpect colo command, expect:%d, but got cmd:%d",
+                     require, cmd);
+        return -EINVAL;
+    }
+
+    *value = qemu_get_be64(f);
+    trace_colo_ctl_get(COLOCommand_lookup[cmd], *value);
+    ret = qemu_file_get_error(f);
+
+    return ret;
+}
+
+static int colo_do_checkpoint_transaction(MigrationState *s)
+{
+    int ret;
+    uint64_t value;
+
+    ret = colo_ctl_put(s->to_dst_file, COLO_COMMAND_CHECKPOINT_REQUEST, 0);
+    if (ret < 0) {
+        goto out;
+    }
+
+    ret = colo_ctl_get(s->rp_state.from_dst_file,
+                       COLO_COMMAND_CHECKPOINT_REPLY, &value);
+    if (ret < 0) {
+        goto out;
+    }
+
+    /* TODO: suspend and save vm state to colo buffer */
+
+    ret = colo_ctl_put(s->to_dst_file, COLO_COMMAND_VMSTATE_SEND, 0);
+    if (ret < 0) {
+        goto out;
+    }
+
+    /* TODO: send vmstate to Secondary */
+
+    ret = colo_ctl_get(s->rp_state.from_dst_file,
+                       COLO_COMMAND_VMSTATE_RECEIVED, &value);
+    if (ret < 0) {
+        goto out;
+    }
+
+    ret = colo_ctl_get(s->rp_state.from_dst_file,
+                       COLO_COMMAND_VMSTATE_LOADED, &value);
+    if (ret < 0) {
+        goto out;
+    }
+
+    /* TODO: resume Primary */
+
+out:
+    return ret;
+}
+
 static void colo_process_checkpoint(MigrationState *s)
 {
     int ret = 0;
+    uint64_t value;
 
     s->rp_state.from_dst_file = qemu_file_get_return_path(s->to_dst_file);
     if (!s->rp_state.from_dst_file) {
@@ -45,12 +145,28 @@ static void colo_process_checkpoint(MigrationState *s)
         goto out;
     }
 
+    /*
+     * Wait for Secondary finish loading vm states and enter COLO
+     * restore.
+     */
+    ret = colo_ctl_get(s->rp_state.from_dst_file,
+                       COLO_COMMAND_CHECKPOINT_READY, &value);
+    if (ret < 0) {
+        goto out;
+    }
+
     qemu_mutex_lock_iothread();
     vm_start();
     qemu_mutex_unlock_iothread();
     trace_colo_vm_state_change("stop", "run");
 
-    /*TODO: COLO checkpoint savevm loop*/
+    while (s->state == MIGRATION_STATUS_COLO) {
+        /* start a colo checkpoint */
+        ret = colo_do_checkpoint_transaction(s);
+        if (ret < 0) {
+            goto out;
+        }
+    }
 
 out:
     if (ret < 0) {
@@ -73,10 +189,46 @@ void migrate_start_colo_process(MigrationState *s)
     qemu_mutex_lock_iothread();
 }
 
+/*
+ * return:
+ * 0: start a checkpoint
+ * -1: some error happened, exit colo restore
+ */
+static int colo_wait_handle_cmd(QEMUFile *f, int *checkpoint_request)
+{
+    int ret;
+    uint32_t cmd;
+    uint64_t value;
+
+    ret = colo_ctl_get_cmd(f, &cmd);
+    if (ret < 0) {
+        /* do failover ? */
+        return ret;
+    }
+    /* Fix me: this value should be 0, which is not so good,
+     * should be used for checking ?
+     */
+    value = qemu_get_be64(f);
+    if (value != 0) {
+        error_report("Got unexpected value %" PRIu64 " for '%s' command",
+                     value, COLOCommand_lookup[cmd]);
+        return -EINVAL;
+    }
+
+    switch (cmd) {
+    case COLO_COMMAND_CHECKPOINT_REQUEST:
+        *checkpoint_request = 1;
+        return 0;
+    default:
+        return -EINVAL;
+    }
+}
+
 void *colo_process_incoming_thread(void *opaque)
 {
     MigrationIncomingState *mis = opaque;
     int ret = 0;
+    uint64_t value;
 
     migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
                       MIGRATION_STATUS_COLO);
@@ -93,7 +245,49 @@ void *colo_process_incoming_thread(void *opaque)
     */
     qemu_set_block(qemu_get_fd(mis->from_src_file));
 
-    /* TODO: COLO checkpoint restore loop */
+
+    ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_CHECKPOINT_READY, 0);
+    if (ret < 0) {
+        goto out;
+    }
+
+    while (mis->state == MIGRATION_STATUS_COLO) {
+        int request = 0;
+        int ret = colo_wait_handle_cmd(mis->from_src_file, &request);
+
+        if (ret < 0) {
+            break;
+        } else {
+            if (!request) {
+                continue;
+            }
+        }
+        /* FIXME: This is unnecessary for periodic checkpoint mode */
+        ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_CHECKPOINT_REPLY, 0);
+        if (ret < 0) {
+            goto out;
+        }
+
+        ret = colo_ctl_get(mis->from_src_file, COLO_COMMAND_VMSTATE_SEND,
+                           &value);
+        if (ret < 0) {
+            goto out;
+        }
+
+        /* TODO: read migration data into colo buffer */
+
+        ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_VMSTATE_RECEIVED, 0);
+        if (ret < 0) {
+            goto out;
+        }
+
+        /* TODO: load vm state */
+
+        ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_VMSTATE_LOADED, 0);
+        if (ret < 0) {
+            goto out;
+        }
+    }
 
 out:
     if (ret < 0) {
diff --git a/qapi-schema.json b/qapi-schema.json
index c2f3b63..48a87af 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -722,6 +722,33 @@
 { 'command': 'migrate-start-postcopy' }
 
 ##
+# @COLOCommand
+#
+# The commands for COLO fault tolerance
+#
+# @invalid: unknown command
+#
+# @checkpoint-ready: SVM is ready for checkpointing
+#
+# @checkpoint-request: PVM tells SVM to prepare for new checkpointing
+#
+# @checkpoint-reply: SVM gets PVM's checkpoint request
+#
+# @vmstate-send: VM's state will be sent by PVM.
+#
+# @vmstate-size: The total size of VMstate.
+#
+# @vmstate-received: VM's state has been received by SVM
+#
+# @vmstate-loaded: VM's state has been loaded by SVM
+#
+# Since: 2.6
+##
+{ 'enum': 'COLOCommand',
+  'data': [ 'invalid', 'checkpoint-ready', 'checkpoint-request',
+            'checkpoint-reply', 'vmstate-send', 'vmstate-size',
+            'vmstate-received', 'vmstate-loaded' ] }
+
 # @MouseInfo:
 #
 # Information about a mouse device.
diff --git a/trace-events b/trace-events
index c98d473..f8a0959 100644
--- a/trace-events
+++ b/trace-events
@@ -1579,6 +1579,8 @@ postcopy_ram_incoming_cleanup_join(void) ""
 
 # migration/colo.c
 colo_vm_state_change(const char *old, const char *new) "Change '%s' => '%s'"
+colo_ctl_put(const char *msg, uint64_t value) "Send '%s' cmd, value: %" 
PRIu64""
+colo_ctl_get(const char *msg, uint64_t value) "Receive '%s' cmd, value: %" 
PRIu64""
 
 # kvm-all.c
 kvm_ioctl(int type, void *arg) "type 0x%x, arg %p"
-- 
1.8.3.1