linux-kernel - Re: [PATCH V2 3/5] vDPA: introduce vDPA bus

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Message-ID: <20200211134746.GI4271@mellanox.com>
Date:   Tue, 11 Feb 2020 09:47:46 -0400
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        tiwei.bie@...el.com, maxime.coquelin@...hat.com,
        cunming.liang@...el.com, zhihong.wang@...el.com,
        rob.miller@...adcom.com, xiao.w.wang@...el.com,
        haotian.wang@...ive.com, lingshan.zhu@...el.com,
        eperezma@...hat.com, lulu@...hat.com, parav@...lanox.com,
        kevin.tian@...el.com, stefanha@...hat.com, rdunlap@...radead.org,
        hch@...radead.org, aadam@...hat.com, jiri@...lanox.com,
        shahafs@...lanox.com, hanand@...inx.com, mhabets@...arflare.com
Subject: Re: [PATCH V2 3/5] vDPA: introduce vDPA bus

On Mon, Feb 10, 2020 at 11:56:06AM +0800, Jason Wang wrote:
> +/**
> + * vdpa_register_device - register a vDPA device
> + * Callers must have a succeed call of vdpa_init_device() before.
> + * @vdev: the vdpa device to be registered to vDPA bus
> + *
> + * Returns an error when fail to add to vDPA bus
> + */
> +int vdpa_register_device(struct vdpa_device *vdev)
> +{
> +	int err = device_add(&vdev->dev);
> +
> +	if (err) {
> +		put_device(&vdev->dev);
> +		ida_simple_remove(&vdpa_index_ida, vdev->index);
> +	}

This is a very dangerous construction, I've seen it lead to driver
bugs. Better to require the driver to always do the put_device on
error unwind

The ida_simple_remove should probably be part of the class release
function to make everything work right

> +/**
> + * vdpa_unregister_driver - unregister a vDPA device driver
> + * @drv: the vdpa device driver to be unregistered
> + */
> +void vdpa_unregister_driver(struct vdpa_driver *drv)
> +{
> +	driver_unregister(&drv->driver);
> +}
> +EXPORT_SYMBOL_GPL(vdpa_unregister_driver);
> +
> +static int vdpa_init(void)
> +{
> +	if (bus_register(&vdpa_bus) != 0)
> +		panic("virtio bus registration failed");
> +	return 0;
> +}

Linus will tell you not to kill the kernel - return the error code and
propagate it up to the module init function.

> +/**
> + * vDPA device - representation of a vDPA device
> + * @dev: underlying device
> + * @dma_dev: the actual device that is performing DMA
> + * @config: the configuration ops for this device.
> + * @index: device index
> + */
> +struct vdpa_device {
> +	struct device dev;
> +	struct device *dma_dev;
> +	const struct vdpa_config_ops *config;
> +	int index;

unsigned values shuld be unsigned int

Jason