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>

semihosting/console.c

@@ -43,7 +43,7 @@ static SemihostingConsole console;
 static int console_can_read(void *opaque)
 {
     SemihostingConsole *c = opaque;
-    g_assert(qemu_mutex_iothread_locked());
+    g_assert(bql_locked());
     return (int)fifo8_num_free(&c->fifo);
 }
 
@@ -58,7 +58,7 @@ static void console_wake_up(gpointer data, gpointer user_data)
 static void console_read(void *opaque, const uint8_t *buf, int size)
 {
     SemihostingConsole *c = opaque;
-    g_assert(qemu_mutex_iothread_locked());
+    g_assert(bql_locked());
     while (size-- && !fifo8_is_full(&c->fifo)) {
         fifo8_push(&c->fifo, *buf++);
     }
@@ -70,7 +70,7 @@ bool qemu_semihosting_console_ready(void)
 {
     SemihostingConsole *c = &console;
 
-    g_assert(qemu_mutex_iothread_locked());
+    g_assert(bql_locked());
     return !fifo8_is_empty(&c->fifo);
 }
 
@@ -78,7 +78,7 @@ void qemu_semihosting_console_block_until_ready(CPUState *cs)
 {
     SemihostingConsole *c = &console;
 
-    g_assert(qemu_mutex_iothread_locked());
+    g_assert(bql_locked());
 
     /* Block if the fifo is completely empty. */
     if (fifo8_is_empty(&c->fifo)) {