linux-kernel - Re: [PATCH 8/9] rfkill: Userspace control for airplane mode

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Message-ID: <1455826364.2084.22.camel@sipsolutions.net>
Date:	Thu, 18 Feb 2016 21:12:44 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	João Paulo Rechi Vita <jprvita@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Darren Hart <dvhart@...radead.org>,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
	platform-driver-x86@...r.kernel.org, linux-api@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux@...lessm.com,
	João Paulo Rechi Vita 
	<jprvita@...lessm.com>
Subject: Re: [PATCH 8/9] rfkill: Userspace control for airplane mode

Hi,

Sorry for the delay reviewing this.



On Mon, 2016-02-08 at 10:41 -0500, João Paulo Rechi Vita wrote:
> Provide an interface for the airplane-mode indicator be controlled
> from
> userspace. User has to first acquire the control through
> RFKILL_OP_AIRPLANE_MODE_ACQUIRE and keep the fd open for the whole
> time
> it wants to be in control of the indicator. Closing the fd or using
> RFKILL_OP_AIRPLANE_MODE_RELEASE restores the default policy.

I've come to the conclusion that the new ops are probably the best
thing to do here.

> +Userspace can also override the default airplane-mode indicator
> policy through
> +/dev/rfkill. Control of the airplane mode indicator has to be
> acquired first,
> +using RFKILL_OP_AIRPLANE_MODE_ACQUIRE, and is only available for one
> userspace
> +application at a time. Closing the fd or using
> RFKILL_OP_AIRPLANE_MODE_RELEASE
> +reverts the airplane-mode indicator back to the default kernel
> policy and makes
> +it available for other applications to take control. Changes to the
> +airplane-mode indicator state can be made using
> RFKILL_OP_AIRPLANE_MODE_CHANGE,
> +passing the new value in the 'soft' field of 'struct rfkill_event'.

I don't really see any value in _RELEASE, since an application can just
close the fd? I'd prefer not having the duplicate functionality
and force us to exercise the single code path every time.

>  For further details consult Documentation/ABI/stable/sysfs-class-
> rfkill.
> diff --git a/include/uapi/linux/rfkill.h
> b/include/uapi/linux/rfkill.h
> index 2e00dce..9cb999b 100644
> --- a/include/uapi/linux/rfkill.h
> +++ b/include/uapi/linux/rfkill.h
> @@ -67,6 +67,9 @@ enum rfkill_operation {
>  	RFKILL_OP_DEL,
>  	RFKILL_OP_CHANGE,
>  	RFKILL_OP_CHANGE_ALL,
> +	RFKILL_OP_AIRPLANE_MODE_ACQUIRE,
> +	RFKILL_OP_AIRPLANE_MODE_RELEASE,
> +	RFKILL_OP_AIRPLANE_MODE_CHANGE,
>  };
 
> @@ -1199,7 +1202,7 @@ static ssize_t rfkill_fop_write(struct file
> *file, const char __user *buf,
>  	if (copy_from_user(&ev, buf, count))
>  		return -EFAULT;
>  
> -	if (ev.op != RFKILL_OP_CHANGE && ev.op !=
> RFKILL_OP_CHANGE_ALL)
> +	if (ev.op < RFKILL_OP_CHANGE)
>  		return -EINVAL;

You need to also reject invalid high values, like 27.

>  	mutex_lock(&rfkill_global_mutex);
>  
> +	if (ev.op == RFKILL_OP_AIRPLANE_MODE_ACQUIRE) {
> +		if (rfkill_apm_owned && !data->is_apm_owner) {
> +			count = -EACCES;
> +		} else {
> +			rfkill_apm_owned = true;
> +			data->is_apm_owner = true;
> +		}
> +	}
> +
> +	if (ev.op == RFKILL_OP_AIRPLANE_MODE_RELEASE) {

It would probably be better to simply use "switch (ev.op)" and make the
default case do a reject.

>  	if (ev.op == RFKILL_OP_CHANGE_ALL)
>  		rfkill_update_global_state(ev.type, ev.soft);

Also moving the existing code inside the switch, of course.

johannes