There use makes our code safer so we should mention them.
Signed-off-by: Alex Bennée <alex.ben...@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org>
Reviewed-by: Juan Quintela <quint...@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru>
Message-Id: <20230424092249.58552-19-alex.ben...@linaro.org>
diff --git a/docs/devel/style.rst b/docs/devel/style.rst
index ac2ce42a2f..aa5e083ff8 100644
--- a/docs/devel/style.rst
+++ b/docs/devel/style.rst
@@ -665,6 +665,60 @@ Note that there is no need to provide typedefs for QOM
structures
since these are generated automatically by the QOM declaration macros.
See :ref:`qom` for more details.
+QEMU GUARD macros
+=================
+
+QEMU provides a number of ``_GUARD`` macros intended to make the
+handling of multiple exit paths easier. For example using
+``QEMU_LOCK_GUARD`` to take a lock will ensure the lock is released on
+exit from the function.
+
+.. code-block:: c
+
+ static int my_critical_function(SomeState *s, void *data)
+ {
+ QEMU_LOCK_GUARD(&s->lock);
+ do_thing1(data);
+ if (check_state2(data)) {
+ return -1;
+ }
+ do_thing3(data);
+ return 0;
+ }
+
+will ensure s->lock is released however the function is exited. The
+equivalent code without _GUARD macro makes us to carefully put
+qemu_mutex_unlock() on all exit points:
+
+.. code-block:: c
+
+ static int my_critical_function(SomeState *s, void *data)
+ {
+ qemu_mutex_lock(&s->lock);
+ do_thing1(data);
+ if (check_state2(data)) {
+ qemu_mutex_unlock(&s->lock);
+ return -1;
+ }
+ do_thing3(data);
+ qemu_mutex_unlock(&s->lock);
+ return 0;
+ }
+
+There are often ``WITH_`` forms of macros which more easily wrap
+around a block inside a function.
+
+.. code-block:: c
+
+ WITH_RCU_READ_LOCK_GUARD() {
+ QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) {
+ err = do_the_thing(kid->child);
+ if (err < 0) {
+ return err;
+ }
+ }
+ }
+
Error handling and reporting
============================
--
2.39.2
