From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Wolfgang Bumiller <w.bumiller@proxmox.com>
Date: Thu, 30 Apr 2020 15:55:37 +0200
Subject: [PATCH] move savevm-async back into a coroutine

Move qemu_savevm_state_{header,setup} into the main loop and
the rest of the iteration into a coroutine. The former need
to lock the iothread (and we can't unlock it in the
coroutine), and the latter can't deal with being in a
separate thread, so a coroutine it must be.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
---
 savevm-async.c | 28 +++++++++-------------------
 1 file changed, 9 insertions(+), 19 deletions(-)

diff --git a/savevm-async.c b/savevm-async.c
index a38b15d652..af865b9a0a 100644
--- a/savevm-async.c
+++ b/savevm-async.c
@@ -51,7 +51,7 @@ static struct SnapshotState {
     QEMUFile *file;
     int64_t total_time;
     QEMUBH *cleanup_bh;
-    QemuThread thread;
+    Coroutine *co;
 } snap_state;
 
 SaveVMInfo *qmp_query_savevm(Error **errp)
@@ -201,11 +201,9 @@ static void process_savevm_cleanup(void *opaque)
     int ret;
     qemu_bh_delete(snap_state.cleanup_bh);
     snap_state.cleanup_bh = NULL;
+    snap_state.co = NULL;
     qemu_savevm_state_cleanup();
 
-    qemu_mutex_unlock_iothread();
-    qemu_thread_join(&snap_state.thread);
-    qemu_mutex_lock_iothread();
     ret = save_snapshot_cleanup();
     if (ret < 0) {
         save_snapshot_error("save_snapshot_cleanup error %d", ret);
@@ -221,18 +219,13 @@ static void process_savevm_cleanup(void *opaque)
     }
 }
 
-static void *process_savevm_thread(void *opaque)
+static void process_savevm_coro(void *opaque)
 {
     int ret;
     int64_t maxlen;
     MigrationState *ms = migrate_get_current();
 
-    rcu_register_thread();
-
-    qemu_savevm_state_header(snap_state.file);
-    qemu_savevm_state_setup(snap_state.file);
     ret = qemu_file_get_error(snap_state.file);
-
     if (ret < 0) {
         save_snapshot_error("qemu_savevm_state_setup failed");
         goto out;
@@ -247,16 +240,13 @@ static void *process_savevm_thread(void *opaque)
         maxlen = blk_getlength(snap_state.target) - 30*1024*1024;
 
         if (pending_size > 400000 && snap_state.bs_pos + pending_size < maxlen) {
-            qemu_mutex_lock_iothread();
             ret = qemu_savevm_state_iterate(snap_state.file, false);
             if (ret < 0) {
                 save_snapshot_error("qemu_savevm_state_iterate error %d", ret);
                 break;
             }
-            qemu_mutex_unlock_iothread();
             DPRINTF("savevm inerate pending size %lu ret %d\n", pending_size, ret);
         } else {
-            qemu_mutex_lock_iothread();
             qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
             ret = global_state_store();
             if (ret) {
@@ -285,16 +275,12 @@ static void *process_savevm_thread(void *opaque)
     }
 
     qemu_bh_schedule(snap_state.cleanup_bh);
-    qemu_mutex_unlock_iothread();
 
 out:
     /* set migration state accordingly and clear soon-to-be stale file */
     migrate_set_state(&ms->state, MIGRATION_STATUS_SETUP,
                       ret ? MIGRATION_STATUS_FAILED : MIGRATION_STATUS_COMPLETED);
     ms->to_dst_file = NULL;
-
-    rcu_unregister_thread();
-    return NULL;
 }
 
 void qmp_savevm_start(bool has_statefile, const char *statefile, Error **errp)
@@ -373,8 +359,12 @@ void qmp_savevm_start(bool has_statefile, const char *statefile, Error **errp)
 
     snap_state.state = SAVE_STATE_ACTIVE;
     snap_state.cleanup_bh = qemu_bh_new(process_savevm_cleanup, &snap_state);
-    qemu_thread_create(&snap_state.thread, "savevm-async", process_savevm_thread,
-                       NULL, QEMU_THREAD_JOINABLE);
+    snap_state.co = qemu_coroutine_create(&process_savevm_coro, NULL);
+    qemu_mutex_unlock_iothread();
+    qemu_savevm_state_header(snap_state.file);
+    qemu_savevm_state_setup(snap_state.file);
+    qemu_mutex_lock_iothread();
+    aio_co_schedule(iohandler_get_aio_context(), snap_state.co);
 
     return;