migration: introduce SaveVMHandlers.resume_prepare

This is hook function to be called when a postcopy migration wants to
resume from a failure. For each module, it should provide its own
recovery logic before we switch to the postcopy-active state.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180502104740.12123-16-peterx@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

include/migration/register.h

@@ -64,6 +64,8 @@ typedef struct SaveVMHandlers {
     LoadStateHandler *load_state;
     int (*load_setup)(QEMUFile *f, void *opaque);
     int (*load_cleanup)(void *opaque);
+    /* Called when postcopy migration wants to resume from failure */
+    int (*resume_prepare)(MigrationState *s, void *opaque);
 } SaveVMHandlers;
 
 int register_savevm_live(DeviceState *dev,

migration/migration.c

@@ -2454,7 +2454,25 @@ typedef enum MigThrError {
 /* Return zero if success, or <0 for error */
 static int postcopy_do_resume(MigrationState *s)
 {
-    /* TODO: do the resume logic */
+    int ret;
+
+    /*
+     * Call all the resume_prepare() hooks, so that modules can be
+     * ready for the migration resume.
+     */
+    ret = qemu_savevm_state_resume_prepare(s);
+    if (ret) {
+        error_report("%s: resume_prepare() failure detected: %d",
+                     __func__, ret);
+        return ret;
+    }
+
+    /*
+     * TODO: handshake with dest using MIG_CMD_RESUME,
+     * MIG_RP_MSG_RESUME_ACK, then switch source state to
+     * "postcopy-active"
+     */
+
     return 0;
 }
 

migration/savevm.c

@@ -1031,6 +1031,31 @@ void qemu_savevm_state_setup(QEMUFile *f)
     }
 }
 
+int qemu_savevm_state_resume_prepare(MigrationState *s)
+{
+    SaveStateEntry *se;
+    int ret;
+
+    trace_savevm_state_resume_prepare();
+
+    QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
+        if (!se->ops || !se->ops->resume_prepare) {
+            continue;
+        }
+        if (se->ops && se->ops->is_active) {
+            if (!se->ops->is_active(se->opaque)) {
+                continue;
+            }
+        }
+        ret = se->ops->resume_prepare(s, se->opaque);
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
+    return 0;
+}
+
 /*
  * this function has three return values:
  *   negative: there was one error, and we have -errno.

migration/savevm.h

@@ -31,6 +31,7 @@
 
 bool qemu_savevm_state_blocked(Error **errp);
 void qemu_savevm_state_setup(QEMUFile *f);
+int qemu_savevm_state_resume_prepare(MigrationState *s);
 void qemu_savevm_state_header(QEMUFile *f);
 int qemu_savevm_state_iterate(QEMUFile *f, bool postcopy);
 void qemu_savevm_state_cleanup(void);

migration/trace-events

@@ -39,6 +39,7 @@ savevm_send_postcopy_run(void) ""
 savevm_send_postcopy_resume(void) ""
 savevm_send_recv_bitmap(char *name) "%s"
 savevm_state_setup(void) ""
+savevm_state_resume_prepare(void) ""
 savevm_state_header(void) ""
 savevm_state_iterate(void) ""
 savevm_state_cleanup(void) ""