On Fri, 20 Mar 2020 13:46:04 -0700 Yonghyun Hwang <yonghyun@xxxxxxxxxx> wrote: > 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. Does this last comment suggest the parent device is not being multiplexed through mdev, but only mediated? If so, would something like Yan's vendor-ops approach[1] be better? Without a multiplexed device, the lifecycle management of an mdev device doesn't make a lot of sense, and I wonder if that's what you're trying to bypass here. Even SR-IOV devices have moved to userspace enablement with most module options to enable a default number of VFs being deprecated. I do see that that transition left a gap, but I'm not sure that heading in the opposite direction with mdevs is a good idea either. Thanks, Alex [1]https://lore.kernel.org/kvm/20200131020803.27519-1-yan.y.zhao@xxxxxxxxx/ > > > 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 */ > > >
