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>

util/main-loop.c

@@ -299,13 +299,13 @@ static int os_host_main_loop_wait(int64_t timeout)
 
     glib_pollfds_fill(&timeout);
 
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     replay_mutex_unlock();
 
     ret = qemu_poll_ns((GPollFD *)gpollfds->data, gpollfds->len, timeout);
 
     replay_mutex_lock();
-    qemu_mutex_lock_iothread();
+    bql_lock();
 
     glib_pollfds_poll();
 
@@ -514,7 +514,7 @@ static int os_host_main_loop_wait(int64_t timeout)
 
     poll_timeout_ns = qemu_soonest_timeout(poll_timeout_ns, timeout);
 
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     replay_mutex_unlock();
 
@@ -522,7 +522,7 @@ static int os_host_main_loop_wait(int64_t timeout)
 
     replay_mutex_lock();
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     if (g_poll_ret > 0) {
         for (i = 0; i < w->num; i++) {
             w->revents[i] = poll_fds[n_poll_fds + i].revents;