migration_init: Fix lock initialisation/make it explicit

Peter reported a lock error on MacOS after my a82d593
patch.

migrate_get_current does one-time initialisation of
a bunch of variables.
migrate_init does reinitialisation even on a 2nd
migrate after a cancel.

The problem here was that I'd initialised the mutex
in migrate_get_current, and the memset in migrate_init
corrupted it.

Remove the memset and replace it by explicit initialisation
of fields that need initialising; this also turns out to be simpler
than the old code that had to preserve some fields.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Fixes: a82d593
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

migration/migration.c

@@ -902,38 +902,31 @@ bool migration_in_postcopy(MigrationState *s)
 MigrationState *migrate_init(const MigrationParams *params)
 {
     MigrationState *s = migrate_get_current();
-    int64_t bandwidth_limit = s->bandwidth_limit;
-    bool enabled_capabilities[MIGRATION_CAPABILITY_MAX];
-    int64_t xbzrle_cache_size = s->xbzrle_cache_size;
-    int compress_level = s->parameters[MIGRATION_PARAMETER_COMPRESS_LEVEL];
-    int compress_thread_count =
-            s->parameters[MIGRATION_PARAMETER_COMPRESS_THREADS];
-    int decompress_thread_count =
-            s->parameters[MIGRATION_PARAMETER_DECOMPRESS_THREADS];
-    int x_cpu_throttle_initial =
-            s->parameters[MIGRATION_PARAMETER_X_CPU_THROTTLE_INITIAL];
-    int x_cpu_throttle_increment =
-            s->parameters[MIGRATION_PARAMETER_X_CPU_THROTTLE_INCREMENT];
-
-    memcpy(enabled_capabilities, s->enabled_capabilities,
-           sizeof(enabled_capabilities));
 
-    memset(s, 0, sizeof(*s));
+    /*
+     * Reinitialise all migration state, except
+     * parameters/capabilities that the user set, and
+     * locks.
+     */
+    s->bytes_xfer = 0;
+    s->xfer_limit = 0;
+    s->cleanup_bh = 0;
+    s->file = NULL;
+    s->state = MIGRATION_STATUS_NONE;
     s->params = *params;
-    memcpy(s->enabled_capabilities, enabled_capabilities,
-           sizeof(enabled_capabilities));
-    s->xbzrle_cache_size = xbzrle_cache_size;
-
-    s->parameters[MIGRATION_PARAMETER_COMPRESS_LEVEL] = compress_level;
-    s->parameters[MIGRATION_PARAMETER_COMPRESS_THREADS] =
-               compress_thread_count;
-    s->parameters[MIGRATION_PARAMETER_DECOMPRESS_THREADS] =
-               decompress_thread_count;
-    s->parameters[MIGRATION_PARAMETER_X_CPU_THROTTLE_INITIAL] =
-                x_cpu_throttle_initial;
-    s->parameters[MIGRATION_PARAMETER_X_CPU_THROTTLE_INCREMENT] =
-                x_cpu_throttle_increment;
-    s->bandwidth_limit = bandwidth_limit;
+    s->rp_state.from_dst_file = NULL;
+    s->rp_state.error = false;
+    s->mbps = 0.0;
+    s->downtime = 0;
+    s->expected_downtime = 0;
+    s->dirty_pages_rate = 0;
+    s->dirty_bytes_rate = 0;
+    s->setup_time = 0;
+    s->dirty_sync_count = 0;
+    s->start_postcopy = false;
+    s->migration_thread_running = false;
+    s->last_req_rb = NULL;
+
     migrate_set_state(s, MIGRATION_STATUS_NONE, MIGRATION_STATUS_SETUP);
 
     QSIMPLEQ_INIT(&s->src_page_requests);