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Date: Thu, 29 Feb 2024 12:47:59 +0100
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH V4 3/5] misc: mlx5ctl: Add info ioctl
Content-Language: en-US
To: Saeed Mahameed <saeed@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-api@vger.kernel.org,
        Linux Documentation <linux-doc@vger.kernel.org>
Cc: Leon Romanovsky <leonro@nvidia.com>, Jason Gunthorpe <jgg@nvidia.com>,
        Jiri Pirko <jiri@nvidia.com>, Leonid Bloch <lbloch@nvidia.com>,
        Itay Avraham <itayavr@nvidia.com>, Jakub Kicinski <kuba@kernel.org>,
        Saeed Mahameed <saeedm@nvidia.com>, David Ahern <dsahern@kernel.org>,
        Aron Silverton <aron.silverton@oracle.com>,
        Christoph Hellwig <hch@infradead.org>, andrew.gospodarek@broadcom.com,
        linux-kernel@vger.kernel.org
References: <20240207072435.14182-1-saeed@kernel.org>
 <20240207072435.14182-4-saeed@kernel.org>
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On 07/02/2024 08:24, Saeed Mahameed wrote:
> +static int mlx5ctl_info_ioctl(struct file *file,
> +			      struct mlx5ctl_info __user *arg,
> +			      size_t usize)
> +{
> +	struct mlx5ctl_fd *mfd = file->private_data;
> +	size_t ksize = sizeof(struct mlx5ctl_info);
> +	struct mlx5ctl_dev *mcdev = mfd->mcdev;
> +	struct mlx5_core_dev *mdev = mcdev->mdev;
> +	struct mlx5ctl_info *info;
> +	int err = 0;
> +
> +	if (usize < ksize)
> +		return -EINVAL;
> +
> +	info = kzalloc(ksize, GFP_KERNEL);
> +	if (!info)
> +		return -ENOMEM;

struct mlx5ctl_info is small, why not put it on the stack or even copy
it directly from the original object, assuming it has no holes/padding?

> +
> +	info->dev_uctx_cap = MLX5_CAP_GEN(mdev, uctx_cap);
> +	info->uctx_cap = mfd->uctx_cap;
> +	info->uctx_uid = mfd->uctx_uid;
> +	info->ucap = mfd->ucap;
> +
> +	if (copy_to_user(arg, info, ksize))
> +		err = -EFAULT;
> +
> +	kfree(info);
> +	return err;
> +}

Is there even a remote possibility of extending this structure in the
future? If so the size check will not allow you to be backwards
compatible. Should there be a version field in there or would you
just add a new ioctl altogether? Adding linux-api@vger.kernel.org to Cc.

> diff --git a/include/uapi/misc/mlx5ctl.h b/include/uapi/misc/mlx5ctl.h
> new file mode 100644
> index 000000000000..9be944128025
> --- /dev/null
> +++ b/include/uapi/misc/mlx5ctl.h
> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0 WITH Linux-syscall-note */
> +/* Copyright (c) 2023, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
> +
> +#ifndef __MLX5CTL_IOCTL_H__
> +#define __MLX5CTL_IOCTL_H__
> +
> +struct mlx5ctl_info {
> +	__u16 uctx_uid; /* current process allocated UCTX UID */
> +	__u16 reserved1; /* explicit padding must be zero */
> +	__u32 uctx_cap; /* current process effective UCTX cap */
> +	__u32 dev_uctx_cap; /* device's UCTX capabilities */
> +	__u32 ucap; /* process user capability */
> +};
> +
> +#define MLX5CTL_IOCTL_MAGIC 0x5c
> +
> +#define MLX5CTL_IOCTL_INFO \
> +	_IOR(MLX5CTL_IOCTL_MAGIC, 0x0, struct mlx5ctl_info)
> +
> +#endif /* __MLX5CTL_IOCTL_H__ */

Should you add anything to Documentation/ABI/ ? (Or add other
documentation for this driver?)


Vegard