Re: [PATCH for-next 1/2] RDMA/uverbs: Add a common way to create CQ with umem

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Jul 01, 2025 at 11:15:44PM +0000, Michael Margolin wrote:
> Add ioctl command attributes and a common handling for the option to
> create CQs with memory buffers passed from userspace. When required
> attributes are supplied, create umem for driver use and store it in CQ
> context.
> The extension enables creation of CQs on top of preallocated CPU
> virtual or device memory buffers, by supplying VA or dmabuf fd, in a
> common way. At first stage the command fails for any driver that didn't
> explicitly state its support by setting a flag in the ops struct.
> 
> Signed-off-by: Michael Margolin <mrgolin@amazon.com>
> ---
>  drivers/infiniband/core/device.c              |  3 +
>  drivers/infiniband/core/uverbs_std_types_cq.c | 82 ++++++++++++++++++-
>  include/rdma/ib_verbs.h                       |  6 ++
>  include/uapi/rdma/ib_user_ioctl_cmds.h        |  4 +
>  4 files changed, 91 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
> index 468ed6bd4722..8b0ce0ec15dd 100644
> --- a/drivers/infiniband/core/device.c
> +++ b/drivers/infiniband/core/device.c
> @@ -2667,6 +2667,9 @@ void ib_set_device_ops(struct ib_device *dev, const struct ib_device_ops *ops)
>  	dev_ops->uverbs_no_driver_id_binding |=
>  		ops->uverbs_no_driver_id_binding;
>  
> +	dev_ops->uverbs_support_cq_with_umem |=
> +		ops->uverbs_support_cq_with_umem;

This seems to have turned out quite nice!

I might just suggest a tweak to streamline this flow

Add:

+       int (*create_cq_umem)(struct ib_cq *cq,
+                             const struct ib_cq_init_attr *attr,
+                             struct ib_umem *umem,
+                             struct uverbs_attr_bundle *attrs);


Instead of the uverbs_support_cq_with_umem

Then the core code would check the two ops and if only umem is present
it will insist on the new attributes, if it is not present it will
refuse them otherwise it will call the correct op.

In the driver the create_cq would obtain the umem from the private
attrs and then call create_cq_umem() in the same way

So it becomes quite easy to just reorganize the drivers to support
this.

Jason