system/cpus: rename qemu_mutex_lock_iothread() to bql_lock()

The Big QEMU Lock (BQL) has many names and they are confusing. The
actual QemuMutex variable is called qemu_global_mutex but it's commonly
referred to as the BQL in discussions and some code comments. The
locking APIs, however, are called qemu_mutex_lock_iothread() and
qemu_mutex_unlock_iothread().

The "iothread" name is historic and comes from when the main thread was
split into into KVM vcpu threads and the "iothread" (now called the main
loop thread). I have contributed to the confusion myself by introducing
a separate --object iothread, a separate concept unrelated to the BQL.

The "iothread" name is no longer appropriate for the BQL. Rename the
locking APIs to:
- void bql_lock(void)
- void bql_unlock(void)
- bool bql_locked(void)

There are more APIs with "iothread" in their names. Subsequent patches
will rename them. There are also comments and documentation that will be
updated in later patches.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Acked-by: Fabiano Rosas <farosas@suse.de>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Peter Xu <peterx@redhat.com>
Acked-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Acked-by: Hyman Huang <yong.huang@smartx.com>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-id: 20240102153529.486531-2-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 26 insertions, 26 deletions

diff --git a/migration/migration.c b/migration/migration.c
index 454cd4ec1f..be173cd0f9 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1283,12 +1283,12 @@ static void migrate_fd_cleanup(MigrationState *s)
         QEMUFile *tmp;
 
         trace_migrate_fd_cleanup();
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         if (s->migration_thread_running) {
             qemu_thread_join(&s->thread);
             s->migration_thread_running = false;
         }
-        qemu_mutex_lock_iothread();
+        bql_lock();
 
         multifd_save_cleanup();
         qemu_mutex_lock(&s->qemu_file_lock);
@@ -2396,7 +2396,7 @@ static int postcopy_start(MigrationState *ms, Error **errp)
     }
 
     trace_postcopy_start();
-    qemu_mutex_lock_iothread();
+    bql_lock();
     trace_postcopy_start_set_run();
 
     migration_downtime_start(ms);
@@ -2504,7 +2504,7 @@ static int postcopy_start(MigrationState *ms, Error **errp)
 
     migration_downtime_end(ms);
 
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     if (migrate_postcopy_ram()) {
         /*
@@ -2545,7 +2545,7 @@ fail:
             error_report_err(local_err);
         }
     }
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     return -1;
 }
 
@@ -2579,14 +2579,14 @@ static int migration_maybe_pause(MigrationState *s,
      * wait for the 'pause_sem' semaphore.
      */
     if (s->state != MIGRATION_STATUS_CANCELLING) {
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         migrate_set_state(&s->state, *current_active_state,
                           MIGRATION_STATUS_PRE_SWITCHOVER);
         qemu_sem_wait(&s->pause_sem);
         migrate_set_state(&s->state, MIGRATION_STATUS_PRE_SWITCHOVER,
                           new_state);
         *current_active_state = new_state;
-        qemu_mutex_lock_iothread();
+        bql_lock();
     }
 
     return s->state == new_state ? 0 : -EINVAL;
@@ -2597,7 +2597,7 @@ static int migration_completion_precopy(MigrationState *s,
 {
     int ret;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     migration_downtime_start(s);
 
     s->vm_old_state = runstate_get();
@@ -2624,7 +2624,7 @@ static int migration_completion_precopy(MigrationState *s,
     ret = qemu_savevm_state_complete_precopy(s->to_dst_file, false,
                                              s->block_inactive);
 out_unlock:
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     return ret;
 }
 
@@ -2632,9 +2632,9 @@ static void migration_completion_postcopy(MigrationState *s)
 {
     trace_migration_completion_postcopy_end();
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     qemu_savevm_state_complete_postcopy(s->to_dst_file);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     /*
      * Shutdown the postcopy fast path thread.  This is only needed when dest
@@ -2658,14 +2658,14 @@ static void migration_completion_failed(MigrationState *s,
          */
         Error *local_err = NULL;
 
-        qemu_mutex_lock_iothread();
+        bql_lock();
         bdrv_activate_all(&local_err);
         if (local_err) {
             error_report_err(local_err);
         } else {
             s->block_inactive = false;
         }
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
     }
 
     migrate_set_state(&s->state, current_active_state,
@@ -3105,7 +3105,7 @@ static void migration_iteration_finish(MigrationState *s)
     /* If we enabled cpu throttling for auto-converge, turn it off. */
     cpu_throttle_stop();
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     switch (s->state) {
     case MIGRATION_STATUS_COMPLETED:
         migration_calculate_complete(s);
@@ -3136,7 +3136,7 @@ static void migration_iteration_finish(MigrationState *s)
         break;
     }
     migrate_fd_cleanup_schedule(s);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 }
 
 static void bg_migration_iteration_finish(MigrationState *s)
@@ -3148,7 +3148,7 @@ static void bg_migration_iteration_finish(MigrationState *s)
      */
     ram_write_tracking_stop();
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     switch (s->state) {
     case MIGRATION_STATUS_COMPLETED:
         migration_calculate_complete(s);
@@ -3167,7 +3167,7 @@ static void bg_migration_iteration_finish(MigrationState *s)
     }
 
     migrate_fd_cleanup_schedule(s);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 }
 
 /*
@@ -3289,9 +3289,9 @@ static void *migration_thread(void *opaque)
     object_ref(OBJECT(s));
     update_iteration_initial_status(s);
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     qemu_savevm_state_header(s->to_dst_file);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     /*
      * If we opened the return path, we need to make sure dst has it
@@ -3319,9 +3319,9 @@ static void *migration_thread(void *opaque)
         qemu_savevm_send_colo_enable(s->to_dst_file);
     }
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     qemu_savevm_state_setup(s->to_dst_file);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP,
                                MIGRATION_STATUS_ACTIVE);
@@ -3432,10 +3432,10 @@ static void *bg_migration_thread(void *opaque)
     ram_write_tracking_prepare();
 #endif
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     qemu_savevm_state_header(s->to_dst_file);
     qemu_savevm_state_setup(s->to_dst_file);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP,
                                MIGRATION_STATUS_ACTIVE);
@@ -3445,7 +3445,7 @@ static void *bg_migration_thread(void *opaque)
     trace_migration_thread_setup_complete();
     migration_downtime_start(s);
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
 
     s->vm_old_state = runstate_get();
 
@@ -3483,7 +3483,7 @@ static void *bg_migration_thread(void *opaque)
     s->vm_start_bh = qemu_bh_new(bg_migration_vm_start_bh, s);
     qemu_bh_schedule(s->vm_start_bh);
 
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     while (migration_is_active(s)) {
         MigIterateState iter_state = bg_migration_iteration_run(s);
@@ -3512,7 +3512,7 @@ fail:
     if (early_fail) {
         migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
                 MIGRATION_STATUS_FAILED);
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
     }
 
     bg_migration_iteration_finish(s);