On Fri, Mar 20, 2020 at 11:34 AM Alex Williamson
<alex.williamson@xxxxxxxxxx> wrote:
>
> On Fri, 20 Mar 2020 10:59:10 -0700
> Yonghyun Hwang <yonghyun@xxxxxxxxxx> wrote:
>
> > To enable a mediated device, a device driver registers its device to VFIO
> > MDev framework. Once the mediated device gets enabled, UUID gets fed onto
> > the sysfs attribute, "create", to create the mediated device. This
> > additional step happens after boot-up gets complete. If the driver knows
> > how many mediated devices need to be created during probing time, the
> > additional step becomes cumbersome. This commit implements a new function
> > to allow the driver to create a mediated device in kernel.
>
> But pre-creating mdev devices seems like a policy decision. Why can't
> userspace make such a policy decision, and do so with persistent uuids,
> via something like mdevctl? Thanks,
>
> Alex
Yep, it can be viewed as the policy decision and userspace can make
the decision. However, it would be handy and plausible, if a device
driver can pre-create "fixed or default" # of mdev devices, while
allowing the device policy to come into play after bootup gets
complete. Without this patch, a device driver should release the
policy and the policy should be aligned with the driver, which would
be cumbersome (sometimes painful) in a cloud environment. My use case
with mdev is to enable a subset of vfio-pci features without losing my
device driver.
Thank you,
Yonghyun
>
>
> > Signed-off-by: Yonghyun Hwang <yonghyun@xxxxxxxxxx>
> > ---
> > drivers/vfio/mdev/mdev_core.c | 45 +++++++++++++++++++++++++++++++++++
> > include/linux/mdev.h | 3 +++
> > 2 files changed, 48 insertions(+)
> >
> > diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> > index b558d4cfd082..a6d32516de42 100644
> > --- a/drivers/vfio/mdev/mdev_core.c
> > +++ b/drivers/vfio/mdev/mdev_core.c
> > @@ -350,6 +350,51 @@ int mdev_device_create(struct kobject *kobj,
> > return ret;
> > }
> >
> > +/*
> > + * mdev_create_device : Create a mdev device
> > + * @dev: device structure representing parent device.
> > + * @uuid: uuid char string for a mdev device.
> > + * @group: index to supported type groups for a mdev device.
> > + *
> > + * Create a mdev device in kernel.
> > + * Returns a negative value on error, otherwise 0.
> > + */
> > +int mdev_create_device(struct device *dev,
> > + const char *uuid, int group)
> > +{
> > + struct mdev_parent *parent = NULL;
> > + struct mdev_type *type = NULL;
> > + guid_t guid;
> > + int i = 1;
> > + int ret;
> > +
> > + ret = guid_parse(uuid, &guid);
> > + if (ret) {
> > + dev_err(dev, "Failed to parse UUID");
> > + return ret;
> > + }
> > +
> > + parent = __find_parent_device(dev);
> > + if (!parent) {
> > + dev_err(dev, "Failed to find parent mdev device");
> > + return -ENODEV;
> > + }
> > +
> > + list_for_each_entry(type, &parent->type_list, next) {
> > + if (i == group)
> > + break;
> > + i++;
> > + }
> > +
> > + if (!type || i != group) {
> > + dev_err(dev, "Failed to find mdev device");
> > + return -ENODEV;
> > + }
> > +
> > + return mdev_device_create(&type->kobj, parent->dev, &guid);
> > +}
> > +EXPORT_SYMBOL(mdev_create_device);
> > +
> > int mdev_device_remove(struct device *dev)
> > {
> > struct mdev_device *mdev, *tmp;
> > diff --git a/include/linux/mdev.h b/include/linux/mdev.h
> > index 0ce30ca78db0..b66f67998916 100644
> > --- a/include/linux/mdev.h
> > +++ b/include/linux/mdev.h
> > @@ -145,4 +145,7 @@ struct device *mdev_parent_dev(struct mdev_device *mdev);
> > struct device *mdev_dev(struct mdev_device *mdev);
> > struct mdev_device *mdev_from_dev(struct device *dev);
> >
> > +extern int mdev_create_device(struct device *dev,
> > + const char *uuid, int group_idx);
> > +
> > #endif /* MDEV_H */
>
