Re: [PATCH rdma-next 1/6] RDMA/uverbs: Introduce UCAP (User CAPabilities) API

[Leon Romanovsky <leon@kernel.org>]

On Wed, Feb 26, 2025 at 04:17:27PM +0200, Leon Romanovsky wrote:
> From: Chiara Meiohas <cmeiohas@nvidia.com>
> 
> Implement a new User CAPabilities (UCAP) API to provide fine-grained
> control over specific firmware features.
> 
> This approach offers more granular capabilities than the existing Linux
> capabilities, which may be too generic for certain FW features.
> 
> This mechanism represents each capability as a character device with
> root read-write access. Root processes can grant users special
> privileges by allowing access to these character devices (e.g., using
> chown).
> 
> UCAP character devices are located in /dev/infiniband and the class path
> is /sys/class/infiniband_ucaps.
> 
> Signed-off-by: Chiara Meiohas <cmeiohas@nvidia.com>
> Reviewed-by: Yishai Hadas <yishaih@nvidia.com>
> Signed-off-by: Leon Romanovsky <leon@kernel.org>
> ---
>  drivers/infiniband/core/Makefile      |   3 +-
>  drivers/infiniband/core/ucaps.c       | 255 ++++++++++++++++++++++++++
>  drivers/infiniband/core/uverbs_main.c |   2 +
>  include/rdma/ib_ucaps.h               |  25 +++
>  4 files changed, 284 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/infiniband/core/ucaps.c
>  create mode 100644 include/rdma/ib_ucaps.h

<...>

> +/**
> + * ib_remove_ucap - Remove a ucap character device
> + * @type: User cap type
> + *
> + * Removes the ucap character device according to type. The device is completely
> + * removed from the filesystem when its reference count reaches 0.
> + */
> +void ib_remove_ucap(enum rdma_user_cap type)
> +{
> +	struct ib_ucap *ucap;
> +
> +	mutex_lock(&ucaps_mutex);
> +	ucap = ucaps_list[type];
> +	if (WARN_ON(!ucap))
> +		goto end;
> +
> +	ucap->refcount--;
> +	if (ucap->refcount)
> +		goto end;
> +
> +	ucaps_list[type] = NULL;
> +	cdev_device_del(&ucap->cdev, &ucap->dev);
> +	put_device(&ucap->dev);

This is kref release pattern, please use it.

> +
> +end:
> +	mutex_unlock(&ucaps_mutex);
> +}
> +EXPORT_SYMBOL(ib_remove_ucap);

Thanks