Subject: Re: [PATCH v7 11/12] vduse: Introduce VDUSE - vDPA Device in Userspace

From: Greg KH <[email-masked]>
Date: Mon, 31 May 2021 06:56:26 +0200

On Mon, May 17, 2021 at 05:55:12PM +0800, Xie Yongji wrote:
> +struct vduse_dev {
> +	struct vduse_vdpa *vdev;
> +	struct device dev;
> +	struct cdev cdev;

You now have 2 reference counted devices controling the lifespace of a
single structure.  A mess that is guaranteed to go wrong.  Please never
do this.

> +	struct vduse_virtqueue *vqs;
> +	struct vduse_iova_domain *domain;
> +	char *name;
> +	struct mutex lock;
> +	spinlock_t msg_lock;
> +	atomic64_t msg_unique;

Why do you need an atomic and a lock?

> +	wait_queue_head_t waitq;
> +	struct list_head send_list;
> +	struct list_head recv_list;
> +	struct list_head list;
> +	struct vdpa_callback config_cb;
> +	struct work_struct inject;
> +	spinlock_t irq_lock;
> +	unsigned long api_version;
> +	bool connected;
> +	int minor;
> +	u16 vq_size_max;
> +	u32 vq_num;
> +	u32 vq_align;
> +	u32 config_size;
> +	u32 device_id;
> +	u32 vendor_id;
> +};
> +
> +struct vduse_dev_msg {
> +	struct vduse_dev_request req;
> +	struct vduse_dev_response resp;
> +	struct list_head list;
> +	wait_queue_head_t waitq;
> +	bool completed;
> +};
> +
> +struct vduse_control {
> +	unsigned long api_version;

u64?

> +};
> +
> +static unsigned long max_bounce_size = (64 * 1024 * 1024);
> +module_param(max_bounce_size, ulong, 0444);
> +MODULE_PARM_DESC(max_bounce_size, "Maximum bounce buffer size. (default: 64M)");
> +
> +static unsigned long max_iova_size = (128 * 1024 * 1024);
> +module_param(max_iova_size, ulong, 0444);
> +MODULE_PARM_DESC(max_iova_size, "Maximum iova space size (default: 128M)");
> +
> +static bool allow_unsafe_device_emulation;
> +module_param(allow_unsafe_device_emulation, bool, 0444);
> +MODULE_PARM_DESC(allow_unsafe_device_emulation, "Allow emulating unsafe device."
> +	" We must make sure the userspace device emulation process is trusted."
> +	" Otherwise, don't enable this option. (default: false)");
> +

This is not the 1990's anymore, please never use module parameters, make
these per-device attributes if you really need them.

> +static int vduse_init(void)
> +{
> +	int ret;
> +
> +	if (max_bounce_size >= max_iova_size)
> +		return -EINVAL;
> +
> +	ret = misc_register(&vduse_misc);
> +	if (ret)
> +		return ret;
> +
> +	vduse_class = class_create(THIS_MODULE, "vduse");

If you have a misc device, you do not need to create a class at the same
time.  Why are you doing both here?  Just stick with the misc device, no
need for anything else.

> +	if (IS_ERR(vduse_class)) {
> +		ret = PTR_ERR(vduse_class);
> +		goto err_class;
> +	}
> +	vduse_class->devnode = vduse_devnode;
> +
> +	ret = alloc_chrdev_region(&vduse_major, 0, VDUSE_DEV_MAX, "vduse");

Wait, you want a whole major?  What is the misc device for?

> +MODULE_VERSION(DRV_VERSION);

MODULE_VERSION() makes no sense when the code is merged into the kernel
tree, so you can just drop that.

thanks,

greg k-h