[PATCH v3 01/25] main-loop.h: introduce qemu_in_main_thread()

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

When invoked from the main loop, this function is the same
as qemu_mutex_iothread_locked, and returns true if the BQL is held.
When invoked from iothreads or tests, it returns true only
if the current AioContext is the Main Loop.

This essentially just extends qemu_mutex_iothread_locked to work
also in unit tests or other users like storage-daemon, that run
in the Main Loop but end up using the implementation in
stubs/iothread-lock.c.

Using qemu_mutex_iothread_locked in unit tests defaults to false
because they use the implementation in stubs/iothread-lock,
making all assertions added in next patches fail despite the
AioContext is still the main loop.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 include/qemu/main-loop.h | 13 +++++++++++++
 softmmu/cpus.c           |  5 +++++
 stubs/iothread-lock.c    |  5 +++++
 3 files changed, 23 insertions(+)

diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h
index 8dbc6fcb89..6b8fa57c5d 100644
--- a/include/qemu/main-loop.h
+++ b/include/qemu/main-loop.h
@@ -245,6 +245,19 @@ AioContext *iohandler_get_aio_context(void);
  */
 bool qemu_mutex_iothread_locked(void);
 
+/**
+ * qemu_in_main_thread: same as qemu_mutex_iothread_locked when
+ * softmmu/cpus.c implementation is linked. Otherwise this function
+ * checks that the current AioContext is the global AioContext
+ * (main loop).
+ *
+ * This is useful when checking that the BQL is held, to avoid
+ * returning false when invoked by unit tests or other users like
+ * storage-daemon that end up using stubs/iothread-lock.c
+ * implementation.
+ */
+bool qemu_in_main_thread(void);
+
 /**
  * qemu_mutex_lock_iothread: Lock the main loop mutex.
  *
diff --git a/softmmu/cpus.c b/softmmu/cpus.c
index 071085f840..3f61a3c31d 100644
--- a/softmmu/cpus.c
+++ b/softmmu/cpus.c
@@ -481,6 +481,11 @@ bool qemu_mutex_iothread_locked(void)
     return iothread_locked;
 }
 
+bool qemu_in_main_thread(void)
+{
+    return qemu_mutex_iothread_locked();
+}
+
 /*
  * The BQL is taken from so many places that it is worth profiling the
  * callers directly, instead of funneling them all through a single function.
diff --git a/stubs/iothread-lock.c b/stubs/iothread-lock.c
index 5b45b7fc8b..ff7386e42c 100644
--- a/stubs/iothread-lock.c
+++ b/stubs/iothread-lock.c
@@ -6,6 +6,11 @@ bool qemu_mutex_iothread_locked(void)
     return false;
 }
 
+bool qemu_in_main_thread(void)
+{
+    return qemu_get_current_aio_context() == qemu_get_aio_context();
+}
+
 void qemu_mutex_lock_iothread_impl(const char *file, int line)
 {
 }
-- 
2.27.0