Re: [PATCH v2 03/14] vfio: Split creation of a vfio_device into init and register ops

On 3/13/2021 2:55 AM, Jason Gunthorpe wrote:

This makes the struct vfio_pci_device part of the public interface so it
can be used with container_of and so forth, as is typical for a Linux
subystem.

This is the first step to bring some type-safety to the vfio interface by
allowing the replacement of 'void *' and 'struct device *' inputs with a
simple and clear 'struct vfio_pci_device *'

For now the self-allocating vfio_add_group_dev() interface is kept so each
user can be updated as a separate patch.

The expected usage pattern is

   driver core probe() function:
      my_device = kzalloc(sizeof(*mydevice));
      vfio_init_group_dev(&my_device->vdev, dev, ops, mydevice);
      /* other driver specific prep */
      vfio_register_group_dev(&my_device->vdev);
      dev_set_drvdata(my_device);

   driver core remove() function:
      my_device = dev_get_drvdata(dev);
      vfio_unregister_group_dev(&my_device->vdev);
      /* other driver specific tear down */
      kfree(my_device);

Allowing the driver to be able to use the drvdata and vifo_device to go
to/from its own data.

The pattern also makes it clear that vfio_register_group_dev() must be
last in the sequence, as once it is called the core code can immediately
start calling ops. The init/register gap is provided to allow for the
driver to do setup before ops can be called and thus avoid races.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Liu Yi L <redacted>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
  Documentation/driver-api/vfio.rst |  31 ++++----
  drivers/vfio/vfio.c               | 123 ++++++++++++++++--------------
  include/linux/vfio.h              |  16 ++++
  3 files changed, 98 insertions(+), 72 deletions(-)

With comments from Cornelia and Kevin, looks good.

Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com>