netdev - Re: [net-next 1/9] Implementation of Virtual Bus

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Message-ID: <20200417195148.GL26002@ziepe.ca>
Date:   Fri, 17 Apr 2020 16:51:48 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Cc:     davem@...emloft.net, gregkh@...uxfoundation.org,
        Dave Ertman <david.m.ertman@...el.com>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, nhorman@...hat.com,
        sassmann@...hat.com, parav@...lanox.com, galpress@...zon.com,
        selvin.xavier@...adcom.com, sriharsha.basavapatna@...adcom.com,
        benve@...co.com, bharat@...lsio.com, xavier.huwei@...wei.com,
        yishaih@...lanox.com, leonro@...lanox.com, mkalderon@...vell.com,
        aditr@...are.com, ranjani.sridharan@...ux.intel.com,
        pierre-louis.bossart@...ux.intel.com,
        Kiran Patil <kiran.patil@...el.com>,
        Andrew Bowers <andrewx.bowers@...el.com>
Subject: Re: [net-next 1/9] Implementation of Virtual Bus

On Fri, Apr 17, 2020 at 10:10:26AM -0700, Jeff Kirsher wrote:

> +/**
> + * virtbus_release_device - Destroy a virtbus device
> + * @_dev: device to release
> + */
> +static void virtbus_release_device(struct device *_dev)
> +{
> +	struct virtbus_device *vdev = to_virtbus_dev(_dev);
> +
> +	ida_simple_remove(&virtbus_dev_ida, vdev->id);
> +	vdev->release(vdev);

This order should probably be swapped (store vdev->id on the stack)

> +/**
> + * virtbus_register_device - add a virtual bus device
> + * @vdev: virtual bus device to add
> + */
> +int virtbus_register_device(struct virtbus_device *vdev)
> +{
> +	int ret;
> +
> +	/* Do this first so that all error paths perform a put_device */
> +	device_initialize(&vdev->dev);
> +
> +	if (!vdev->release) {
> +		ret = -EINVAL;
> +		dev_err(&vdev->dev, "virtbus_device MUST have a .release callback that does something.\n");
> +		goto device_pre_err;

This does put_device but the release() hasn't been set yet. Doesn't it
leak memory?

> +	}
> +
> +	/* All device IDs are automatically allocated */
> +	ret = ida_simple_get(&virtbus_dev_ida, 0, 0, GFP_KERNEL);
> +	if (ret < 0) {
> +		dev_err(&vdev->dev, "get IDA idx for virtbus device failed!\n");
> +		goto device_pre_err;

Do this before device_initialize()

> +	}
> +
> +
> +	vdev->dev.bus = &virtual_bus_type;
> +	vdev->dev.release = virtbus_release_device;

And this immediately after

> +
> +	vdev->id = ret;
> +	dev_set_name(&vdev->dev, "%s.%d", vdev->name, vdev->id);

Missing check of return code

Can't understand why vdev->name is being passed in with the struct,
why not just a function argument?

> +	dev_dbg(&vdev->dev, "Registering virtbus device '%s'\n",
> +		dev_name(&vdev->dev));
> +
> +	ret = device_add(&vdev->dev);
> +	if (ret)
> +		goto device_add_err;

This looks like it does ida_simple_remove twice, once in the goto and
once from the release function called by put_device.

> +/**
> + * virtbus_unregister_device - remove a virtual bus device
> + * @vdev: virtual bus device we are removing
> + */
> +void virtbus_unregister_device(struct virtbus_device *vdev)
> +{
> +	device_del(&vdev->dev);
> +	put_device(&vdev->dev);
> +}
> +EXPORT_SYMBOL_GPL(virtbus_unregister_device);

Just inline this as wrapper around device_unregister

> +/**
> + * __virtbus_register_driver - register a driver for virtual bus devices
> + * @vdrv: virtbus_driver structure
> + * @owner: owning module/driver
> + */
> +int __virtbus_register_driver(struct virtbus_driver *vdrv, struct module *owner)
> +{
> +	if (!vdrv->probe || !vdrv->remove || !vdrv->shutdown || !vdrv->id_table)
> +		return -EINVAL;
> +
> +	vdrv->driver.owner = owner;
> +	vdrv->driver.bus = &virtual_bus_type;
> +	vdrv->driver.probe = virtbus_probe_driver;
> +	vdrv->driver.remove = virtbus_remove_driver;
> +	vdrv->driver.shutdown = virtbus_shutdown_driver;
> +	vdrv->driver.suspend = virtbus_suspend_driver;
> +	vdrv->driver.resume = virtbus_resume_driver;
> +
> +	return driver_register(&vdrv->driver);
> +}
> +EXPORT_SYMBOL_GPL(__virtbus_register_driver);
> +
> +/**
> + * virtbus_unregister_driver - unregister a driver for virtual bus devices
> + * @vdrv: virtbus_driver structure
> + */
> +void virtbus_unregister_driver(struct virtbus_driver *vdrv)
> +{
> +	driver_unregister(&vdrv->driver);
> +}
> +EXPORT_SYMBOL_GPL(virtbus_unregister_driver);

Also just inline this

> diff --git a/include/linux/virtual_bus.h b/include/linux/virtual_bus.h
> new file mode 100644
> index 000000000000..4df06178e72f
> +++ b/include/linux/virtual_bus.h
> @@ -0,0 +1,53 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * virtual_bus.h - lightweight software bus
> + *
> + * Copyright (c) 2019-20 Intel Corporation
> + *
> + * Please see Documentation/driver-api/virtual_bus.rst for more information
> + */
> +
> +#ifndef _VIRTUAL_BUS_H_
> +#define _VIRTUAL_BUS_H_
> +
> +#include <linux/device.h>
> +
> +struct virtbus_device {
> +	struct device dev;
> +	const char *name;
> +	void (*release)(struct virtbus_device *);
> +	int id;

id can't be negative

> +int virtbus_register_device(struct virtbus_device *vdev);
> +void virtbus_unregister_device(struct virtbus_device *vdev);

I continue to think the alloc/register pattern, eg as demonstrated by
vdpa_alloc_device() and vdpa_register_device() is easier for drivers
to implement correctly.

> +int
> +__virtbus_register_driver(struct virtbus_driver *vdrv, struct module *owner);
> +void virtbus_unregister_driver(struct virtbus_driver *vdrv);
> +
> +#define virtbus_register_driver(vdrv) \
> +	__virtbus_register_driver(vdrv, THIS_MODULE)
> +

It is reasonable to also provide a module_driver() macro.

Jason