[Qemu-devel] [PATCH COLO-Frame v13 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>
Cc: Markus Armbruster <address@hidden>
Cc: Dr. David Alan Gilbert <address@hidden>
---
v13:
- Refactor colo command related helper functions, use 'Error **errp' parameter
  instead of return value to indicate success or failure.
- Fix some other comments from Markus.

v12:
- Rename colo_ctl_put() to colo_put_cmd()
- Rename colo_ctl_get() to colo_get_check_cmd() and drop
  the third parameter
- Rename colo_ctl_get_cmd() to colo_get_cmd()
- Remove useless 'invalid' member for COLOcommand enum.
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 | 201 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 qapi-schema.json |  25 +++++++
 trace-events     |   2 +
 3 files changed, 226 insertions(+), 2 deletions(-)

diff --git a/migration/colo.c b/migration/colo.c
index 65ac0c9..c76e1fa 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -10,6 +10,7 @@
  * later.  See the COPYING file in the top-level directory.
  */
 
+#include <unistd.h>
 #include "sysemu/sysemu.h"
 #include "migration/colo.h"
 #include "trace.h"
@@ -34,22 +35,147 @@ bool migration_incoming_in_colo_state(void)
     return mis && (mis->state == MIGRATION_STATUS_COLO);
 }
 
+static void colo_put_cmd(QEMUFile *f, COLOCommand cmd,
+                         Error **errp)
+{
+    int ret;
+
+    if (cmd >= COLO_COMMAND__MAX) {
+        error_setg(errp, "%s: Invalid cmd", __func__);
+        return;
+    }
+    qemu_put_be32(f, cmd);
+    qemu_fflush(f);
+
+    ret = qemu_file_get_error(f);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Can't put COLO command");
+    }
+    trace_colo_put_cmd(COLOCommand_lookup[cmd]);
+}
+
+static COLOCommand colo_get_cmd(QEMUFile *f, Error **errp)
+{
+    COLOCommand cmd;
+    int ret;
+
+    cmd = qemu_get_be32(f);
+    ret = qemu_file_get_error(f);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Can't get COLO command");
+        return cmd;
+    }
+    if (cmd >= COLO_COMMAND__MAX) {
+        error_setg(errp, "%s: Invalid cmd", __func__);
+        return cmd;
+    }
+    trace_colo_get_cmd(COLOCommand_lookup[cmd]);
+    return cmd;
+}
+
+static void colo_get_check_cmd(QEMUFile *f, COLOCommand expect_cmd,
+                               Error **errp)
+{
+    COLOCommand cmd;
+    Error *local_err = NULL;
+
+    cmd = colo_get_cmd(f, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+    if (cmd != expect_cmd) {
+        error_setg(errp, "Unexpected COLO command %d, expected %d",
+                          expect_cmd, cmd);
+    }
+}
+
+static int colo_do_checkpoint_transaction(MigrationState *s)
+{
+    Error *local_err = NULL;
+
+    colo_put_cmd(s->to_dst_file, COLO_COMMAND_CHECKPOINT_REQUEST,
+                 &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    colo_get_check_cmd(s->rp_state.from_dst_file,
+                       COLO_COMMAND_CHECKPOINT_REPLY, &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    /* TODO: suspend and save vm state to colo buffer */
+
+    colo_put_cmd(s->to_dst_file, COLO_COMMAND_VMSTATE_SEND, &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    /* TODO: send vmstate to Secondary */
+
+    colo_get_check_cmd(s->rp_state.from_dst_file,
+                       COLO_COMMAND_VMSTATE_RECEIVED, &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    colo_get_check_cmd(s->rp_state.from_dst_file,
+                       COLO_COMMAND_VMSTATE_LOADED, &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    /* TODO: resume Primary */
+
+    return 0;
+out:
+    if (local_err) {
+        error_report_err(local_err);
+    }
+    return -EINVAL;
+}
+
 static void colo_process_checkpoint(MigrationState *s)
 {
+    Error *local_err = NULL;
+    int ret;
+
     s->rp_state.from_dst_file = qemu_file_get_return_path(s->to_dst_file);
     if (!s->rp_state.from_dst_file) {
         error_report("Open QEMUFile from_dst_file failed");
         goto out;
     }
 
+    /*
+     * Wait for Secondary finish loading vm states and enter COLO
+     * restore.
+     */
+    colo_get_check_cmd(s->rp_state.from_dst_file,
+                       COLO_COMMAND_CHECKPOINT_READY, &local_err);
+    if (local_err) {
+        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:
+    /* Throw the unreported error message after exited from loop */
+    if (local_err) {
+        error_report_err(local_err);
+    }
     migrate_set_state(&s->state, MIGRATION_STATUS_COLO,
                       MIGRATION_STATUS_COMPLETED);
 
@@ -67,9 +193,33 @@ void migrate_start_colo_process(MigrationState *s)
     qemu_mutex_lock_iothread();
 }
 
+static void colo_wait_handle_cmd(QEMUFile *f, int *checkpoint_request,
+                                 Error **errp)
+{
+    COLOCommand cmd;
+    Error *local_err = NULL;
+
+    cmd = colo_get_cmd(f, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    switch (cmd) {
+    case COLO_COMMAND_CHECKPOINT_REQUEST:
+        *checkpoint_request = 1;
+        break;
+    default:
+        *checkpoint_request = 0;
+        error_setg(errp, "Got unknown COLO command: %d", cmd);
+        break;
+    }
+}
+
 void *colo_process_incoming_thread(void *opaque)
 {
     MigrationIncomingState *mis = opaque;
+    Error *local_err = NULL;
 
     migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
                       MIGRATION_STATUS_COLO);
@@ -85,9 +235,56 @@ void *colo_process_incoming_thread(void *opaque)
     */
     qemu_file_set_blocking(mis->from_src_file, true);
 
-    /* TODO: COLO checkpoint restore loop */
+    colo_put_cmd(mis->to_src_file, COLO_COMMAND_CHECKPOINT_READY,
+                 &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    while (mis->state == MIGRATION_STATUS_COLO) {
+        int request;
+
+        colo_wait_handle_cmd(mis->from_src_file, &request, &local_err);
+        if (local_err) {
+            goto out;
+        }
+        assert(request);
+        /* FIXME: This is unnecessary for periodic checkpoint mode */
+        colo_put_cmd(mis->to_src_file, COLO_COMMAND_CHECKPOINT_REPLY,
+                     &local_err);
+        if (local_err) {
+            goto out;
+        }
+
+        colo_get_check_cmd(mis->from_src_file,
+                           COLO_COMMAND_VMSTATE_SEND, &local_err);
+        if (local_err) {
+            goto out;
+        }
+
+        /* TODO: read migration data into colo buffer */
+
+        colo_put_cmd(mis->to_src_file, COLO_COMMAND_VMSTATE_RECEIVED,
+                     &local_err);
+        if (local_err) {
+            goto out;
+        }
+
+        /* TODO: load vm state */
+
+        colo_put_cmd(mis->to_src_file, COLO_COMMAND_VMSTATE_LOADED,
+                     &local_err);
+        if (local_err) {
+            goto out;
+        }
+    }
 
 out:
+    /* Throw the unreported error message after exited from loop */
+    if (local_err) {
+        error_report_err(local_err);
+    }
+
     if (mis->to_src_file) {
         qemu_fclose(mis->to_src_file);
     }
diff --git a/qapi-schema.json b/qapi-schema.json
index 6eefad2..4ea4108 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -718,6 +718,31 @@
 { 'command': 'migrate-start-postcopy' }
 
 ##
+# @COLOCommand
+#
+# The commands for COLO fault tolerance
+#
+# @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': [ '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 57ddc8f..51b2305 100644
--- a/trace-events
+++ b/trace-events
@@ -1581,6 +1581,8 @@ postcopy_ram_incoming_cleanup_join(void) ""
 
 # migration/colo.c
 colo_vm_state_change(const char *old, const char *new) "Change '%s' => '%s'"
+colo_put_cmd(const char *msg) "Send '%s' cmd"
+colo_get_cmd(const char *msg) "Receive '%s' cmd"
 
 # kvm-all.c
 kvm_ioctl(int type, void *arg) "type 0x%x, arg %p"
-- 
1.8.3.1