linux-kernel - Re: [PATCHv4 10/17] pps: use BUG_ON for kernel API safety checks

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Date:	Sat, 20 Nov 2010 17:13:51 +0100
From:	Rodolfo Giometti <giometti@...eenne.com>
To:	Alexander Gordeev <lasaine@....cs.msu.su>
Cc:	linux-kernel@...r.kernel.org,
	"Nikita V. Youshchenko" <yoush@...msu.su>,
	linuxpps@...enneenne.com, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCHv4 10/17] pps: use BUG_ON for kernel API safety checks

On Thu, Nov 18, 2010 at 07:01:03PM +0300, Alexander Gordeev wrote:
> This way less overhead is involved when running production kernel.
> If you want to debug a pps client module please define DEBUG to enable
> the checks.
> 
> Signed-off-by: Alexander Gordeev <lasaine@....cs.msu.su>
> ---
>  drivers/pps/kapi.c |   33 ++++++++++-----------------------
>  1 files changed, 10 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c
> index fe832aa..54261c4 100644
> --- a/drivers/pps/kapi.c
> +++ b/drivers/pps/kapi.c
> @@ -81,25 +81,14 @@ struct pps_device *pps_register_source(struct pps_source_info *info,
>  	int err;
>  
>  	/* Sanity checks */
> -	if ((info->mode & default_params) != default_params) {
> -		pr_err("pps: %s: unsupported default parameters\n",
> -					info->name);
> -		err = -EINVAL;
> -		goto pps_register_source_exit;
> -	}
> -	if ((info->mode & (PPS_ECHOASSERT | PPS_ECHOCLEAR)) != 0 &&
> -			info->echo == NULL) {
> -		pr_err("pps: %s: echo function is not defined\n",
> -					info->name);
> -		err = -EINVAL;
> -		goto pps_register_source_exit;
> -	}
> -	if ((info->mode & (PPS_TSFMT_TSPEC | PPS_TSFMT_NTPFP)) == 0) {
> -		pr_err("pps: %s: unspecified time format\n",
> -					info->name);
> -		err = -EINVAL;
> -		goto pps_register_source_exit;
> -	}
> +
> +	/* default_params should be supported */
> +	BUG_ON((info->mode & default_params) != default_params);
> +	/* echo function should be defined if we are asked to call it */
> +	BUG_ON((info->mode & (PPS_ECHOASSERT | PPS_ECHOCLEAR)) != 0 &&
> +			info->echo == NULL);
> +	/* time format should be specified */
> +	BUG_ON((info->mode & (PPS_TSFMT_TSPEC | PPS_TSFMT_NTPFP)) == 0);

Nack.

If the userland gives us some wrong parameters this is not the same of
a kernel bug (which BUG_ON is used for). The userland must be notified
about the wrong input.

>  	/* Allocate memory for the new PPS source struct */
>  	pps = kzalloc(sizeof(struct pps_device), GFP_KERNEL);
> @@ -179,10 +168,8 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event,
>  	int captured = 0;
>  	struct pps_ktime ts_real;
>  
> -	if ((event & (PPS_CAPTUREASSERT | PPS_CAPTURECLEAR)) == 0) {
> -		dev_err(pps->dev, "unknown event (%x)\n", event);
> -		return;
> -	}
> +	/* check event type */
> +	BUG_ON((event & (PPS_CAPTUREASSERT | PPS_CAPTURECLEAR)) == 0);

Ack.

This is a correct usage of BUG_ON. :)

>  	dev_dbg(pps->dev, "PPS event at %ld.%09ld\n",
>  			ts->ts_real.tv_sec, ts->ts_real.tv_nsec);
> -- 
> 1.7.2.3
> 

Ciao,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail: giometti@...eenne.com
Linux Device Driver                          giometti@...ux.it
Embedded Systems                     phone:  +39 349 2432127
UNIX programming                     skype:  rodolfo.giometti
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