[RFC PATCH 1/2] kunit: resource: Add kunit_defer() functionality

[David Gow <davidgow@google.com>]

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

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

Signed-off-by: David Gow <davidgow@google.com>
---
 include/kunit/resource.h |  87 +++++++++++++++++++++++++++++++
 lib/kunit/resource.c     | 110 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 197 insertions(+)

diff --git a/include/kunit/resource.h b/include/kunit/resource.h
index cf6fb8f2ac1b..6c4728ca9237 100644
--- a/include/kunit/resource.h
+++ b/include/kunit/resource.h
@@ -387,4 +387,91 @@ static inline int kunit_destroy_named_resource(struct kunit *test,
  */
 void kunit_remove_resource(struct kunit *test, struct kunit_resource *res);
 
+typedef void (*kunit_defer_function_t)(void *ctx);
+
+/**
+ * kunit_defer() - Defer a function call until the test ends.
+ * @test: Test case to associate the deferred function with.
+ * @func: The function to run on test exit
+ * @ctx: Data passed into @func
+ * @internal_gfp: gfp to use for internal allocations, if unsure, use GFP_KERNEL
+ *
+ * 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_defer() will execute in the opposite order to that
+ * they were registered in.
+ *
+ * This is useful for cleaning up allocated memory and resources.
+ *
+ * RETURNS:
+ *   An opaque "cancellation token", or NULL on error. Pass this token to
+ *   kunit_defer_cancel() in order to cancel the deferred execution of func().
+ */
+void *kunit_defer(struct kunit *test, kunit_defer_function_t func,
+		  void *ctx, gfp_t internal_gfp);
+
+/**
+ * kunit_defer_cancel_token() - Cancel a deferred function call.
+ * @test: Test case the deferred function is associated with.
+ * @cancel_token: The cancellation token returned by kunit_defer()
+ *
+ * Prevent a function deferred using kunit_defer() from executing when the
+ * test ends.
+ *
+ * Prefer using this to kunit_defer_cancel() where possible.
+ */
+void kunit_defer_cancel_token(struct kunit *test, void *cancel_token);
+
+/**
+ * kunit_defer_trigger_token() - Run a deferred function call immediately.
+ * @test: Test case the deferred function is associated with.
+ * @cancel_token: The cancellation token returned by kunit_defer()
+ *
+ * Execute a deferred function call immediately, instead of waiting for the
+ * test to end.
+ *
+ * Prefer using this to kunit_defer_trigger() where possible.
+ */
+void kunit_defer_trigger_token(struct kunit *test, void *cancel_token);
+
+/**
+ * kunit_defer_cancel() - Cancel a matching deferred function call.
+ * @test: Test case the deferred function is associated with.
+ * @func: The deferred function to cancel.
+ * @ctx: The context passed to the deferred function to trigger.
+ *
+ * Prevent a function deferred via kunit_defer() from executing at shutdown.
+ * Unlike kunit_defer_cancel_token(), this takes the (func, ctx) pair instead of
+ * the cancellation token. If that function/context pair was deferred multiple
+ * times, only the most recent one will be cancelled.
+ *
+ * Prefer using kunit_defer_cancel_token() to this where possible.
+ */
+void kunit_defer_cancel(struct kunit *test,
+			kunit_defer_function_t func,
+			void *ctx);
+
+/**
+ * kunit_defer_trigger() - Run a matching deferred function call immediately.
+ * @test: Test case the deferred function 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_defer() immediately, rather than when
+ * the test ends.
+ * Unlike kunit_defer_trigger_token(), this takes the (func, ctx) pair instead of
+ * the cancellation token. If that 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_defer_trigger(test, func, ctx);
+ * is equivalent to
+ * func(ctx);
+ * kunit_defer_cancel(test, func, ctx);
+ *
+ * Prefer using kunit_defer_trigger_token() to this where possible.
+ */
+void kunit_defer_trigger(struct kunit *test,
+			 kunit_defer_function_t func,
+			 void *ctx);
 #endif /* _KUNIT_RESOURCE_H */
diff --git a/lib/kunit/resource.c b/lib/kunit/resource.c
index c414df922f34..0d0c48054d45 100644
--- a/lib/kunit/resource.c
+++ b/lib/kunit/resource.c
@@ -77,3 +77,113 @@ int kunit_destroy_resource(struct kunit *test, kunit_resource_match_t match,
 	return 0;
 }
 EXPORT_SYMBOL_GPL(kunit_destroy_resource);
+
+struct kunit_defer_ctx {
+	kunit_defer_function_t func;
+	void *ctx;
+};
+
+static void __kunit_defer_free(struct kunit_resource *res)
+{
+	struct kunit_defer_ctx *defer_ctx = (struct kunit_defer_ctx *)res->data;
+
+	defer_ctx->func(defer_ctx->ctx);
+
+	kfree(res->data);
+}
+
+void *kunit_defer(struct kunit *test, kunit_defer_function_t func,
+				void *ctx, gfp_t internal_gfp)
+{
+	struct kunit_resource *res;
+	struct kunit_defer_ctx *defer_ctx;
+
+	KUNIT_ASSERT_NOT_NULL_MSG(test, func, "Tried to defer a NULL function!");
+
+	res = kzalloc(sizeof(*res), internal_gfp);
+	if (!res)
+		return NULL;
+
+	defer_ctx = kzalloc(sizeof(*defer_ctx), internal_gfp);
+	if (!defer_ctx)
+		goto free_res;
+
+	defer_ctx->func = func;
+	defer_ctx->ctx = ctx;
+
+	res->should_kfree = true;
+	__kunit_add_resource(test, NULL, __kunit_defer_free, res, defer_ctx);
+
+	return (void *)res;
+
+free_res:
+	kfree(res);
+	return NULL;
+}
+
+void kunit_defer_cancel_token(struct kunit *test, void *cancel_token)
+{
+	struct kunit_resource *res = (struct kunit_resource *)cancel_token;
+
+	/* Remove the free function so we don't run the deferred function. */
+	res->free = NULL;
+
+	kunit_remove_resource(test, res);
+}
+
+void kunit_defer_trigger_token(struct kunit *test, void *cancel_token)
+{
+	struct kunit_resource *res = (struct kunit_resource *)cancel_token;
+
+	/* Removing the resource should trigger the res->free function. */
+	kunit_remove_resource(test, res);
+}
+
+static bool __kunit_defer_match(struct kunit *test,
+				struct kunit_resource *res, void *match_data)
+{
+	struct kunit_defer_ctx *match_ctx = (struct kunit_defer_ctx *)match_data;
+	struct kunit_defer_ctx *res_ctx = (struct kunit_defer_ctx *)res->data;
+
+	/* Make sure this is a free function. */
+	if (res->free != __kunit_defer_free)
+		return false;
+
+	/* Both the function and context data should match. */
+	return (match_ctx->func == res_ctx->func) && (match_ctx->ctx == res_ctx->ctx);
+}
+
+void kunit_defer_cancel(struct kunit *test,
+			kunit_defer_function_t func,
+			void *ctx)
+{
+	struct kunit_defer_ctx defer_ctx;
+	struct kunit_resource *res;
+
+	defer_ctx.func = func;
+	defer_ctx.ctx = ctx;
+
+	res = kunit_find_resource(test, __kunit_defer_match, &defer_ctx);
+	if (res) {
+		kunit_defer_cancel_token(test, res);
+		kunit_put_resource(res);
+	}
+}
+
+void kunit_defer_trigger(struct kunit *test,
+			 kunit_defer_function_t func,
+			 void *ctx)
+{
+	struct kunit_defer_ctx defer_ctx;
+	struct kunit_resource *res;
+
+	defer_ctx.func = func;
+	defer_ctx.ctx = ctx;
+
+	res = kunit_find_resource(test, __kunit_defer_match, &defer_ctx);
+	if (res) {
+		kunit_defer_trigger_token(test, res);
+		/* We have to put() this here, else free won't be called. */
+		kunit_put_resource(res);
+	}
+}
-- 
2.40.0.348.gf938b09366-goog