kunit: Add kunit_add_action() to defer a call until test exit

Many uses of the KUnit resource system are intended to simply defer
calling a function until the test exits (be it due to success or
failure). The existing kunit_alloc_resource() function is often used for
this, but was awkward to use (requiring passing NULL init functions, etc),
and returned a resource without incrementing its reference count, which
-- while okay for this use-case -- could cause problems in others.

Instead, introduce a simple kunit_add_action() API: a simple function
(returning nothing, accepting a single void* argument) can be scheduled
to be called when the test exits. Deferred actions are called in the
opposite order to that which they were registered.

This mimics the devres API, devm_add_action(), and also provides
kunit_remove_action(), to cancel a deferred action, and
kunit_release_action() to trigger one early.

This is implemented as a resource under the hood, so the ordering
between resource cleanup and deferred functions is maintained.

Reviewed-by: Benjamin Berg <benjamin.berg@intel.com>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>
Tested-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

include/kunit/resource.h

@@ -387,4 +387,96 @@ static inline int kunit_destroy_named_resource(struct kunit *test,
  */
 void kunit_remove_resource(struct kunit *test, struct kunit_resource *res);
 
+/* A 'deferred action' function to be used with kunit_add_action. */
+typedef void (kunit_action_t)(void *);
+
+/**
+ * kunit_add_action() - Call a function when the test ends.
+ * @test: Test case to associate the action with.
+ * @func: The function to run on test exit
+ * @ctx: Data passed into @func
+ *
+ * Defer the execution of a function until the test exits, either normally or
+ * due to a failure.  @ctx is passed as additional context. All functions
+ * registered with kunit_add_action() will execute in the opposite order to that
+ * they were registered in.
+ *
+ * This is useful for cleaning up allocated memory and resources, as these
+ * functions are called even if the test aborts early due to, e.g., a failed
+ * assertion.
+ *
+ * See also: devm_add_action() for the devres equivalent.
+ *
+ * Returns:
+ *   0 on success, an error if the action could not be deferred.
+ */
+int kunit_add_action(struct kunit *test, kunit_action_t *action, void *ctx);
+
+/**
+ * kunit_add_action_or_reset() - Call a function when the test ends.
+ * @test: Test case to associate the action with.
+ * @func: The function to run on test exit
+ * @ctx: Data passed into @func
+ *
+ * Defer the execution of a function until the test exits, either normally or
+ * due to a failure.  @ctx is passed as additional context. All functions
+ * registered with kunit_add_action() will execute in the opposite order to that
+ * they were registered in.
+ *
+ * This is useful for cleaning up allocated memory and resources, as these
+ * functions are called even if the test aborts early due to, e.g., a failed
+ * assertion.
+ *
+ * If the action cannot be created (e.g., due to the system being out of memory),
+ * then action(ctx) will be called immediately, and an error will be returned.
+ *
+ * See also: devm_add_action_or_reset() for the devres equivalent.
+ *
+ * Returns:
+ *   0 on success, an error if the action could not be deferred.
+ */
+int kunit_add_action_or_reset(struct kunit *test, kunit_action_t *action,
+			      void *ctx);
+
+/**
+ * kunit_remove_action() - Cancel a matching deferred action.
+ * @test: Test case the action is associated with.
+ * @func: The deferred function to cancel.
+ * @ctx: The context passed to the deferred function to trigger.
+ *
+ * Prevent an action deferred via kunit_add_action() from executing when the
+ * test terminates.
+ *
+ * If the function/context pair was deferred multiple times, only the most
+ * recent one will be cancelled.
+ *
+ * See also: devm_remove_action() for the devres equivalent.
+ */
+void kunit_remove_action(struct kunit *test,
+			 kunit_action_t *action,
+			 void *ctx);
+
+/**
+ * kunit_release_action() - Run a matching action call immediately.
+ * @test: Test case the action is associated with.
+ * @func: The deferred function to trigger.
+ * @ctx: The context passed to the deferred function to trigger.
+ *
+ * Execute a function deferred via kunit_add_action()) immediately, rather than
+ * when the test ends.
+ *
+ * If the function/context pair was deferred multiple times, it will only be
+ * executed once here. The most recent deferral will no longer execute when
+ * the test ends.
+ *
+ * kunit_release_action(test, func, ctx);
+ * is equivalent to
+ * func(ctx);
+ * kunit_remove_action(test, func, ctx);
+ *
+ * See also: devm_release_action() for the devres equivalent.
+ */
+void kunit_release_action(struct kunit *test,
+			  kunit_action_t *action,
+			  void *ctx);
 #endif /* _KUNIT_RESOURCE_H */