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

[Yongji Xie <xieyongji@bytedance.com>]

Hi Greg,

Thanks a lot for the review!

On Mon, May 31, 2021 at 12:56 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> 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.
>

These two are both used by cdev_device_add(). Looks like I didn't find
any problem. Any suggestions?

> > +     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?
>

You are right. We don't need an atomic here.

> > +     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?
>

OK.

> > +};
> > +
> > +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.
>

These parameters will be used before the device is created. Or do you
mean add some attributes to the control device?

> > +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.
>

The misc device is the control device represented by
/dev/vduse/control. Then a VDUSE device represented by
/dev/vduse/$NAME can be created by the ioctl(VDUSE_CREATE_DEV) on this
control device.

> > +     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?
>

The misc device is used for controlling. And VDUSE devices are
allocated in a dynamic chardev range. Or do I need to reserve the
first minor for the control device instead?

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

Will do it.

Thanks,
Yongji