migration: simplify error handling

Always use qemu_file_get_error to detect errors, since that is how
QEMUFile itself drops I/O after an error occurs.  There is no need
to propagate and check return values all the time.

Also remove the "complete" member, since we know that it is set (via
migrate_fd_cleanup) only when the state changes.
Reviewed-by: NOrit Wasserman <owasserm@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NJuan Quintela <quintela@redhat.com>

include/migration/migration.h

@@ -54,7 +54,6 @@ struct MigrationState
     int64_t dirty_bytes_rate;
     bool enabled_capabilities[MIGRATION_CAPABILITY_MAX];
     int64_t xbzrle_cache_size;
-    bool complete;
 };
 
 void process_incoming_migration(QEMUFile *f);

migration.c

@@ -525,6 +525,10 @@ static void buffered_flush(MigrationState *s)
 
     DPRINTF("flushing %zu byte(s) of data\n", s->buffer_size);
 
+    if (qemu_file_get_error(s->file)) {
+        s->buffer_size = 0;
+        return;
+    }
     qemu_fflush(s->file);
 
     while (s->bytes_xfer < s->xfer_limit && offset < s->buffer_size) {
@@ -592,7 +596,6 @@ static int buffered_close(void *opaque)
     while (!qemu_file_get_error(s->file) && s->buffer_size) {
         buffered_flush(s);
     }
-    s->complete = true;
     return migrate_fd_close(s);
 }
 
@@ -656,37 +659,21 @@ static void *buffered_file_thread(void *opaque)
     int64_t sleep_time = 0;
     int64_t max_size = 0;
     bool last_round = false;
-    int ret;
 
     qemu_mutex_lock_iothread();
     DPRINTF("beginning savevm\n");
-    ret = qemu_savevm_state_begin(s->file, &s->params);
-    qemu_mutex_unlock_iothread();
+    qemu_savevm_state_begin(s->file, &s->params);
 
-    while (ret >= 0) {
+    while (s->state == MIG_STATE_ACTIVE) {
         int64_t current_time;
         uint64_t pending_size;
 
-        qemu_mutex_lock_iothread();
-        if (s->state != MIG_STATE_ACTIVE) {
-            DPRINTF("put_ready returning because of non-active state\n");
-            qemu_mutex_unlock_iothread();
-            break;
-        }
-        if (s->complete) {
-            qemu_mutex_unlock_iothread();
-            break;
-        }
         if (s->bytes_xfer < s->xfer_limit) {
             DPRINTF("iterate\n");
             pending_size = qemu_savevm_state_pending(s->file, max_size);
             DPRINTF("pending size %lu max %lu\n", pending_size, max_size);
             if (pending_size && pending_size >= max_size) {
-                ret = qemu_savevm_state_iterate(s->file);
-                if (ret < 0) {
-                    qemu_mutex_unlock_iothread();
-                    break;
-                }
+                qemu_savevm_state_iterate(s->file);
             } else {
                 int old_vm_running = runstate_is_running();
                 int64_t start_time, end_time;
@@ -695,13 +682,8 @@ static void *buffered_file_thread(void *opaque)
                 start_time = qemu_get_clock_ms(rt_clock);
                 qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
                 vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
-                ret = qemu_savevm_state_complete(s->file);
-                if (ret < 0) {
-                    qemu_mutex_unlock_iothread();
-                    break;
-                } else {
-                    migrate_fd_completed(s);
-                }
+                qemu_savevm_state_complete(s->file);
+                migrate_fd_completed(s);
                 end_time = qemu_get_clock_ms(rt_clock);
                 s->total_time = end_time - s->total_time;
                 s->downtime = end_time - start_time;
@@ -740,12 +722,13 @@ static void *buffered_file_thread(void *opaque)
             sleep_time += qemu_get_clock_ms(rt_clock) - current_time;
         }
         buffered_flush(s);
-        ret = qemu_file_get_error(s->file);
+        qemu_mutex_lock_iothread();
+        if (qemu_file_get_error(s->file)) {
+            migrate_fd_error(s);
+        }
     }
 
-    if (ret < 0) {
-        migrate_fd_error(s);
-    }
+    qemu_mutex_unlock_iothread();
     g_free(s->buffer);
     return NULL;
 }
@@ -770,7 +753,6 @@ void migrate_fd_connect(MigrationState *s)
     s->expected_downtime = max_downtime/1000000;
 
     s->xfer_limit = s->bandwidth_limit / XFER_LIMIT_RATIO;
-    s->complete = false;
 
     s->file = qemu_fopen_ops(s, &buffered_file_ops);