Subject: Re: [net-next 3/3] eventpoll: Add epoll ioctl for epoll_params

From: Joe Damato <[email-masked]>
Date: Wed, 24 Jan 2024 07:37:43 -0800

On Wed, Jan 24, 2024 at 02:53:59AM +0000, Joe Damato wrote:
> Add an ioctl for getting and setting epoll_params. User programs can use
> this ioctl to get and set the busy poll usec time or packet budget
> params for a specific epoll context.
> 
> Signed-off-by: Joe Damato <[email-masked]>
> ---
>  .../userspace-api/ioctl/ioctl-number.rst      |  1 +
>  fs/eventpoll.c                                | 41 +++++++++++++++++++
>  include/uapi/linux/eventpoll.h                | 12 ++++++
>  3 files changed, 54 insertions(+)
> 
> diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
> index 457e16f06e04..b33918232f78 100644
> --- a/Documentation/userspace-api/ioctl/ioctl-number.rst
> +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
> @@ -309,6 +309,7 @@ Code  Seq#    Include File                                           Comments
>  0x89  0B-DF  linux/sockios.h
>  0x89  E0-EF  linux/sockios.h                                         SIOCPROTOPRIVATE range
>  0x89  F0-FF  linux/sockios.h                                         SIOCDEVPRIVATE range
> +0x8A  00-1F  linux/eventpoll.h
>  0x8B  all    linux/wireless.h
>  0x8C  00-3F                                                          WiNRADiO driver
>                                                                       <http://www.winradio.com.au/>
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index 40bd97477b91..d973147c015c 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -869,6 +869,45 @@ static void ep_clear_and_put(struct eventpoll *ep)
>  		ep_free(ep);
>  }
>  
> +static long ep_eventpoll_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> +{
> +	int ret;
> +	struct eventpoll *ep;
> +	struct epoll_params epoll_params;
> +	void __user *uarg = (void __user *) arg;
> +
> +	if (!is_file_epoll(file))
> +		return -EINVAL;
> +
> +	ep = file->private_data;
> +
> +	switch (cmd) {
> +#ifdef CONFIG_NET_RX_BUSY_POLL
> +	case EPIOCSPARAMS:
> +		if (copy_from_user(&epoll_params, uarg, sizeof(epoll_params)))
> +			return -EFAULT;
> +
> +		ep->busy_poll_usecs = epoll_params.busy_poll_usecs;
> +		ep->busy_poll_budget = epoll_params.busy_poll_budget;
> +		return 0;
> +
> +	case EPIOCGPARAMS:
> +		memset(&epoll_params, 0, sizeof(epoll_params));
> +		epoll_params.busy_poll_usecs = ep->busy_poll_usecs;
> +		epoll_params.busy_poll_budget = ep->busy_poll_budget;
> +		if (copy_to_user(uarg, &epoll_params, sizeof(epoll_params)))
> +			return -EFAULT;
> +
> +		return 0;
> +#endif
> +	default:
> +		ret = -EINVAL;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
>  static int ep_eventpoll_release(struct inode *inode, struct file *file)
>  {
>  	struct eventpoll *ep = file->private_data;
> @@ -975,6 +1014,8 @@ static const struct file_operations eventpoll_fops = {
>  	.release	= ep_eventpoll_release,
>  	.poll		= ep_eventpoll_poll,
>  	.llseek		= noop_llseek,
> +	.unlocked_ioctl	= ep_eventpoll_ioctl,
> +	.compat_ioctl   = compat_ptr_ioctl,
>  };
>  
>  /*
> diff --git a/include/uapi/linux/eventpoll.h b/include/uapi/linux/eventpoll.h
> index cfbcc4cc49ac..9211103779c4 100644
> --- a/include/uapi/linux/eventpoll.h
> +++ b/include/uapi/linux/eventpoll.h
> @@ -85,4 +85,16 @@ struct epoll_event {
>  	__u64 data;
>  } EPOLL_PACKED;
>  
> +struct epoll_params {
> +	u64 busy_poll_usecs;
> +	u16 busy_poll_budget;
> +
> +	/* for future fields */
> +	uint8_t data[118];

Err, just noticed that this should be a u8, instead. Sorry I missed this.

I assume there will be other feedback to address, but if not, I've noted
that I need to fix this in the v2.