Re: [PATCH 1/4] kunit: Add APIs for managing devices

Greg Kroah-Hartman
2023-12-05T17:30:52Z

On Tue, Dec 05, 2023 at 03:31:33PM +0800, davidgow@google.com wrote:
> Tests for drivers often require a struct device to pass to other
> functions. While it's possible to create these with
> root_device_register(), or to use something like a platform device, this
> is both a misuse of those APIs, and can be difficult to clean up after,
> for example, a failed assertion.
>
> Add some KUnit-specific functions for registering and unregistering a
> struct device:
> - kunit_device_register()
> - kunit_device_register_with_driver()
> - kunit_device_unregister()
>
> These helpers allocate a on a 'kunit' bus which will either probe the
> driver passed in (kunit_device_register_with_driver), or will create a
> stub driver (kunit_device_register) which is cleaned up on test shutdown.
>
> Devices are automatically unregistered on test shutdown, but can be
> manually unregistered earlier with kunit_device_unregister() in order
> to, for example, test device release code.

At first glance, nice work. But looks like 0-day doesn't like it that
much, so I'll wait for the next version to review it properly.

One nit I did notice:

> +// For internal use only -- registers the kunit_bus.
> +int kunit_bus_init(void);

Put stuff like this in a local .h file, don't pollute the include/linux/
files for things that you do not want any other part of the kernel to
call.

> +/**
> + * kunit_device_register_with_driver() - Create a struct device for use in KUnit tests
> + * @test: The test context object.
> + * @name: The name to give the created device.
> + * @drv: The struct device_driver to associate with the device.
> + *
> + * Creates a struct kunit_device (which is a struct device) with the given
> + * name, and driver. The device will be cleaned up on test exit, or when
> + * kunit_device_unregister is called. See also kunit_device_register, if you
> + * wish KUnit to create and manage a driver for you
> + */
> +struct device *kunit_device_register_with_driver(struct kunit *test,
> + const char *name,
> + struct device_driver *drv);

Shouldn't "struct device_driver *" be a constant pointer?

But really, why is this a "raw" device_driver pointer and not a pointer
to the driver type for your bus?

Oh heck, let's point out the other issues as I'm already here...

> @@ -7,7 +7,8 @@ kunit-objs += test.o \
> assert.o \
> try-catch.o \
> executor.o \
> - attributes.o
> + attributes.o \
> + device.o

Shouldn't this file be "bus.c" as you are creating a kunit bus?

>
> ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
> kunit-objs += debugfs.o
> diff --git a/lib/kunit/device.c b/lib/kunit/device.c
> new file mode 100644
> index 000000000000..93ace1a2297d
> --- /dev/null
> +++ b/lib/kunit/device.c
> @@ -0,0 +1,176 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KUnit basic device implementation

"basic bus/driver implementation", not device, right?

> + *
> + * Implementation of struct kunit_device helpers.
> + *
> + * Copyright (C) 2023, Google LLC.
> + * Author: David Gow <davidgow@google.com>
> + */
> +
> +#include <linux/device.h>
> +
> +#include <kunit/test.h>
> +#include <kunit/device.h>
> +#include <kunit/resource.h>
> +
> +
> +/* Wrappers for use with kunit_add_action() */
> +KUNIT_DEFINE_ACTION_WRAPPER(device_unregister_wrapper, device_unregister, struct device *);
> +KUNIT_DEFINE_ACTION_WRAPPER(driver_unregister_wrapper, driver_unregister, struct device_driver *);
> +
> +static struct device kunit_bus = {
> + .init_name = "kunit"
> +};

A static device as a bus? This feels wrong, what is it for? And where
does this live? If you _REALLY_ want a single device for the root of
your bus (which is a good idea), then make it a dynamic variable (as it
is reference counted), NOT a static struct device which should not be
done if at all possible.

> +
> +/* A device owned by a KUnit test. */
> +struct kunit_device {
> + struct device dev;
> + struct kunit *owner;
> + /* Force binding to a specific driver. */
> + struct device_driver *driver;
> + /* The driver is managed by KUnit and unique to this device. */
> + bool cleanup_driver;
> +};

Wait, why isn't your "kunit" device above a struct kunit_device
structure? Why is it ok to be a "raw" struct device (hint, that's
almost never a good idea.)

> +static inline struct kunit_device *to_kunit_device(struct device *d)
> +{
> + return container_of(d, struct kunit_device, dev);

container_of_const()? And to use that properly, why not make this a #define?

> +}
> +
> +static int kunit_bus_match(struct device *dev, struct device_driver *driver)
> +{
> + struct kunit_device *kunit_dev = to_kunit_device(dev);
> +
> + if (kunit_dev->driver == driver)
> + return 1;
> +
> + return 0;

I don't understand, what are you trying to match here?

> +}
> +
> +static struct bus_type kunit_bus_type = {
> + .name = "kunit",
> + .match = kunit_bus_match
> +};
> +
> +int kunit_bus_init(void)
> +{
> + int error;
> +
> + error = bus_register(&kunit_bus_type);
> + if (!error) {
> + error = device_register(&kunit_bus);
> + if (error)
> + bus_unregister(&kunit_bus_type);
> + }
> + return error;
> +}
> +late_initcall(kunit_bus_init);
> +
> +static void kunit_device_release(struct device *d)
> +{
> + kfree(to_kunit_device(d));
> +}
> +
> +struct device_driver *kunit_driver_create(struct kunit *test, const char *name)
> +{
> + struct device_driver *driver;
> + int err = -ENOMEM;
> +
> + driver = kunit_kzalloc(test, sizeof(*driver), GFP_KERNEL);
> +
> + if (!driver)
> + return ERR_PTR(err);
> +
> + driver->name = name;
> + driver->bus = &kunit_bus_type;
> + driver->owner = THIS_MODULE;
> +
> + err = driver_register(driver);
> + if (err) {
> + kunit_kfree(test, driver);
> + return ERR_PTR(err);
> + }
> +
> + kunit_add_action(test, driver_unregister_wrapper, driver);
> + return driver;
> +}
> +EXPORT_SYMBOL_GPL(kunit_driver_create);
> +
> +struct kunit_device *__kunit_device_register_internal(struct kunit *test,
> + const char *name,
> + struct device_driver *drv)
> +{
> + struct kunit_device *kunit_dev;
> + int err = -ENOMEM;
> +
> + kunit_dev = kzalloc(sizeof(struct kunit_device), GFP_KERNEL);
> + if (!kunit_dev)
> + return ERR_PTR(err);
> +
> + kunit_dev->owner = test;
> +
> + err = dev_set_name(&kunit_dev->dev, "%s.%s", test->name, name);
> + if (err) {
> + kfree(kunit_dev);
> + return ERR_PTR(err);
> + }
> +
> + /* Set the expected driver pointer, so we match. */
> + kunit_dev->driver = drv;

Ah, so this is the match function to pass above? If so, why do you need
it at all?

> +
> + kunit_dev->dev.release = kunit_device_release;
> + kunit_dev->dev.bus = &kunit_bus_type;
> + kunit_dev->dev.parent = &kunit_bus;
> +
> + err = device_register(&kunit_dev->dev);
> + if (err) {
> + put_device(&kunit_dev->dev);
> + return ERR_PTR(err);
> + }
> +
> + kunit_add_action(test, device_unregister_wrapper, &kunit_dev->dev);
> +
> + return kunit_dev;
> +}
> +
> +struct device *kunit_device_register_with_driver(struct kunit *test,
> + const char *name,
> + struct device_driver *drv)
> +{
> + struct kunit_device *kunit_dev = __kunit_device_register_internal(test, name, drv);
> +
> + if (IS_ERR_OR_NULL(kunit_dev))

This is almost always a sign that something is wrong with the api.

> + return (struct device *)kunit_dev; /* This is an error or NULL, so is compatible */

Ick, the cast is odd, are you sure you need it? Why would you return a
struct device and not a kunit_device() anyway?

> +
> + return &kunit_dev->dev;

Again, why this type, why not use the real type you have?

thanks,

greg k-h