linux-kernel - Re: [PATCH net-next v6 4/4] eventpoll: Add epoll ioctl for epoll

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Date: Wed, 7 Feb 2024 09:37:14 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: Joe Damato <jdamato@...tly.com>, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org
Cc: chuck.lever@...cle.com, jlayton@...nel.org, linux-api@...r.kernel.org,
 brauner@...nel.org, edumazet@...gle.com, davem@...emloft.net,
 alexander.duyck@...il.com, sridhar.samudrala@...el.com, kuba@...nel.org,
 willemdebruijn.kernel@...il.com, weiwan@...gle.com, David.Laight@...LAB.COM,
 arnd@...db.de, sdf@...gle.com, amritha.nambiar@...el.com,
 Jonathan Corbet <corbet@....net>, Alexander Viro <viro@...iv.linux.org.uk>,
 Jan Kara <jack@...e.cz>, Nathan Lynch <nathanl@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Namjae Jeon <linkinjeon@...nel.org>, Steve French <stfrench@...rosoft.com>,
 Thomas Zimmermann <tzimmermann@...e.de>, Julien Panis <jpanis@...libre.com>,
 Andrew Waterman <waterman@...s.berkeley.edu>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
 "open list:FILESYSTEMS (VFS and infrastructure)"
 <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH net-next v6 4/4] eventpoll: Add epoll ioctl for
 epoll_params

On 05. 02. 24, 22:04, 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, packet budget, and
> prefer busy poll params for a specific epoll context.
> 
> Parameters are limited:
>    - busy_poll_usecs is limited to <= u32_max
>    - busy_poll_budget is limited to <= NAPI_POLL_WEIGHT by unprivileged
>      users (!capable(CAP_NET_ADMIN))
>    - prefer_busy_poll must be 0 or 1
>    - __pad must be 0
> 
> Signed-off-by: Joe Damato <jdamato@...tly.com>
..
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
..
> @@ -497,6 +498,50 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
>   	ep->napi_id = napi_id;
>   }
>   
> +static long ep_eventpoll_bp_ioctl(struct file *file, unsigned int cmd,
> +				  unsigned long arg)
> +{
> +	struct eventpoll *ep;
> +	struct epoll_params epoll_params;
> +	void __user *uarg = (void __user *) arg;
> +
> +	ep = file->private_data;

This might have been on the ep declaration line.

> +	switch (cmd) {
> +	case EPIOCSPARAMS:
> +		if (copy_from_user(&epoll_params, uarg, sizeof(epoll_params)))
> +			return -EFAULT;
> +
> +		if (memchr_inv(epoll_params.__pad, 0, sizeof(epoll_params.__pad)))
> +			return -EINVAL;
> +
> +		if (epoll_params.busy_poll_usecs > U32_MAX)
> +			return -EINVAL;
> +
> +		if (epoll_params.prefer_busy_poll > 1)
> +			return -EINVAL;
> +
> +		if (epoll_params.busy_poll_budget > NAPI_POLL_WEIGHT &&
> +		    !capable(CAP_NET_ADMIN))
> +			return -EPERM;
> +
> +		ep->busy_poll_usecs = epoll_params.busy_poll_usecs;
> +		ep->busy_poll_budget = epoll_params.busy_poll_budget;
> +		ep->prefer_busy_poll = !!epoll_params.prefer_busy_poll;

This !! is unnecessary. Nonzero values shall be "converted" to true.

But FWIW, the above is nothing which should be blocking, so:

Reviewed-by: Jiri Slaby <jirislaby@...nel.org>

> +		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;
> +		epoll_params.prefer_busy_poll = ep->prefer_busy_poll;
> +		if (copy_to_user(uarg, &epoll_params, sizeof(epoll_params)))
> +			return -EFAULT;
> +		return 0;
> +	default:
> +		return -ENOIOCTLCMD;
> +	}
> +}
..
thanks,
-- 
js
suse labs