Re: [PATCH V4 3/6] mdev: introduce device specific ops

Alex Williamson
2019-10-17T17:53:23Z

On Thu, 17 Oct 2019 17:07:55 +0200
Cornelia Huck <cohuck@redhat.com> wrote:

> On Thu, 17 Oct 2019 18:48:33 +0800
> Jason Wang <jasowang@redhat.com> wrote:
>
> > Currently, except for the create and remove, the rest of
> > mdev_parent_ops is designed for vfio-mdev driver only and may not help
> > for kernel mdev driver. With the help of class id, this patch
> > introduces device specific callbacks inside mdev_device
> > structure. This allows different set of callback to be used by
> > vfio-mdev and virtio-mdev.
> >
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > ---
> > .../driver-api/vfio-mediated-device.rst | 25 +++++----
> > MAINTAINERS | 1 +
> > drivers/gpu/drm/i915/gvt/kvmgt.c | 18 ++++---
> > drivers/s390/cio/vfio_ccw_ops.c | 18 ++++---
> > drivers/s390/crypto/vfio_ap_ops.c | 14 +++--
> > drivers/vfio/mdev/mdev_core.c | 18 +++++--
> > drivers/vfio/mdev/mdev_private.h | 1 +
> > drivers/vfio/mdev/vfio_mdev.c | 37 ++++++-------
> > include/linux/mdev.h | 45 ++++------------
> > include/linux/vfio_mdev.h | 52 +++++++++++++++++++
> > samples/vfio-mdev/mbochs.c | 20 ++++---
> > samples/vfio-mdev/mdpy.c | 20 ++++---
> > samples/vfio-mdev/mtty.c | 18 ++++---
> > 13 files changed, 184 insertions(+), 103 deletions(-)
> > create mode 100644 include/linux/vfio_mdev.h
> >
> > diff --git a/Documentation/driver-api/vfio-mediated-device.rst b/Documentation/driver-api/vfio-mediated-device.rst
> > index f9a78d75a67a..0cca84d19603 100644
> > --- a/Documentation/driver-api/vfio-mediated-device.rst
> > +++ b/Documentation/driver-api/vfio-mediated-device.rst
> > @@ -152,11 +152,22 @@ callbacks per mdev parent device, per mdev type, or any other categorization.
> > Vendor drivers are expected to be fully asynchronous in this respect or
> > provide their own internal resource protection.)
> >
> > -The callbacks in the mdev_parent_ops structure are as follows:
> > -
> > -* open: open callback of mediated device
> > -* close: close callback of mediated device
> > -* ioctl: ioctl callback of mediated device
> > +As multiple types of mediated devices may be supported, the device
> > +must set up the class id and the device specific callbacks in create()
>
> s/in create()/in the create()/
>
> > +callback. E.g for vfio-mdev device it needs to be done through:
>
> "Each class provides a helper function to do so; e.g. for vfio-mdev
> devices, the function to be called is:"
>
> ?
>
> > +
> > + int mdev_set_vfio_ops(struct mdev_device *mdev,
> > + const struct vfio_mdev_ops *vfio_ops);
> > +
> > +The class id (set to MDEV_CLASS_ID_VFIO) is used to match a device
>
> "(set by this helper function to MDEV_CLASS_ID_VFIO)" ?
>
> > +with an mdev driver via its id table. The device specific callbacks
> > +(specified in *ops) are obtainable via mdev_get_dev_ops() (for use by
>
> "(specified in *vfio_ops by the caller)" ?
>
> > +the mdev bus driver). A vfio-mdev device (class id MDEV_CLASS_ID_VFIO)
> > +uses the following device-specific ops:
> > +
> > +* open: open callback of vfio mediated device
> > +* close: close callback of vfio mediated device
> > +* ioctl: ioctl callback of vfio mediated device
> > * read : read emulation callback
> > * write: write emulation callback
> > * mmap: mmap emulation callback
> > @@ -167,10 +178,6 @@ register itself with the mdev core driver::
> > extern int mdev_register_device(struct device *dev,
> > const struct mdev_parent_ops *ops);
> >
> > -It is also required to specify the class_id in create() callback through::
> > -
> > - int mdev_set_class(struct mdev_device *mdev, u16 id);
> > -
>
> I'm wondering if this patch set should start out with introducing
> helper functions already (i.e. don't introduce mdev_set_class(), but
> start out with mdev_set_class_vfio() which will gain the *vfio_ops
> argument in this patch.)

Yes, it would be cleaner, but is it really worth the churn? Correct me
if I'm wrong, but I think we get to the same point after this patch and
aside from the function name itself, the difference is really just that
the class_id is briefly exposed to the parent driver, right? Thanks,

Alex

> > However, the mdev_parent_ops structure is not required in the function call
> > that a driver should use to unregister itself with the mdev core driver::
> >
>
> (...)
>
> > diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> > index 3a9c52d71b4e..d0f3113c8071 100644
> > --- a/drivers/vfio/mdev/mdev_core.c
> > +++ b/drivers/vfio/mdev/mdev_core.c
> > @@ -45,15 +45,23 @@ void mdev_set_drvdata(struct mdev_device *mdev, void *data)
> > }
> > EXPORT_SYMBOL(mdev_set_drvdata);
> >
> > -/* Specify the class for the mdev device, this must be called during
> > - * create() callback.
> > +/* Specify the VFIO device ops for the mdev device, this
> > + * must be called during create() callback for VFIO mdev device.
> > */
>
> /*
> * Specify the mdev device to be a VFIO mdev device, and set the
> * VFIO devices ops for it. This must be called from the create()
> * callback for VFIO mdev devices.
> */
>
> ?
>
> > -void mdev_set_class(struct mdev_device *mdev, u16 id)
> > +void mdev_set_vfio_ops(struct mdev_device *mdev,
> > + const struct vfio_mdev_device_ops *vfio_ops)
> > {
> > WARN_ON(mdev->class_id);
> > - mdev->class_id = id;
> > + mdev->class_id = MDEV_CLASS_ID_VFIO;
> > + mdev->device_ops = vfio_ops;
> > }
> > -EXPORT_SYMBOL(mdev_set_class);
> > +EXPORT_SYMBOL(mdev_set_vfio_ops);
> > +
> > +const void *mdev_get_dev_ops(struct mdev_device *mdev)
> > +{
> > + return mdev->device_ops;
> > +}
> > +EXPORT_SYMBOL(mdev_get_dev_ops);
> >
> > struct device *mdev_dev(struct mdev_device *mdev)
> > {
>
> (...)
>
> The code change looks good to me; I'm just wondering if we should
> introduce mdev_set_class() at all (see above).