Re: [RFC 02/20] vfio: Add device class for /dev/vfio/devices

David Gibson
2021-09-29T03:34:01Z

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On Sun, Sep 19, 2021 at 02:38:30PM +0800, Liu Yi L wrote:
> This patch introduces a new interface (/dev/vfio/devices/$DEVICE) for
> userspace to directly open a vfio device w/o relying on container/group
> (/dev/vfio/$GROUP). Anything related to group is now hidden behind
> iommufd (more specifically in iommu core by this RFC) in a device-centric
> manner.
>
> In case a device is exposed in both legacy and new interfaces (see next
> patch for how to decide it), this patch also ensures that when the device
> is already opened via one interface then the other one must be blocked.
>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
[snip]

> +static bool vfio_device_in_container(struct vfio_device *device)
> +{
> + return !!(device->group && device->group->container);

You don't need !! here. && is already a logical operation, so returns
a valid bool.

> +}
> +
> static int vfio_device_fops_release(struct inode *inode, struct file *filep)
> {
> struct vfio_device *device = filep->private_data;
> @@ -1560,7 +1691,16 @@ static int vfio_device_fops_release(struct inode *inode, struct file *filep)
>
> module_put(device->dev->driver->owner);
>
> - vfio_group_try_dissolve_container(device->group);
> + if (vfio_device_in_container(device)) {
> + vfio_group_try_dissolve_container(device->group);
> + } else {
> + atomic_dec(&device->opened);
> + if (device->group) {
> + mutex_lock(&device->group->opened_lock);
> + device->group->opened--;
> + mutex_unlock(&device->group->opened_lock);
> + }
> + }
>
> vfio_device_put(device);
>
> @@ -1613,6 +1753,7 @@ static int vfio_device_fops_mmap(struct file *filep, struct vm_area_struct *vma)
>
> static const struct file_operations vfio_device_fops = {
> .owner = THIS_MODULE,
> + .open = vfio_device_fops_open,
> .release = vfio_device_fops_release,
> .read = vfio_device_fops_read,
> .write = vfio_device_fops_write,
> @@ -2295,6 +2436,52 @@ static struct miscdevice vfio_dev = {
> .mode = S_IRUGO | S_IWUGO,
> };
>
> +static char *vfio_device_devnode(struct device *dev, umode_t *mode)
> +{
> + return kasprintf(GFP_KERNEL, "vfio/devices/%s", dev_name(dev));

Others have pointed out some problems with the use of dev_name()
here. I'll add that I think you'll make things much easier if instead
of using one huge "devices" subdir, you use a separate subdir for each
vfio sub-driver (so, one for PCI, one for each type of mdev, one for
platform, etc.). That should make avoiding name conflicts a lot simpler.

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson

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