linux-kernel - Re: [PATCH v5 2/4] iio: core: Introduce IIO configfs support

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Message-ID: <5547CF8A.9060609@metafoo.de>
Date:	Mon, 04 May 2015 21:59:06 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Daniel Baluta <daniel.baluta@...el.com>, jic23@...nel.org
CC:	jlbec@...lplan.org, knaack.h@....de, linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org, octavian.purdila@...el.com,
	pebolle@...cali.nl, patrick.porlan@...el.com,
	adriana.reus@...el.com, constantin.musca@...el.com,
	marten@...uitiveaerial.com
Subject: Re: [PATCH v5 2/4] iio: core: Introduce IIO configfs support

On 05/04/2015 12:50 PM, Daniel Baluta wrote:
> This creates an IIO configfs subystem named "iio", with a default "triggers"
> group.
>
> Triggers group is used for handling software triggers. To create a new software
> trigger one must create a directory inside the trigger directory.
>
> Software trigger name MUST follow the following convention:
> 	* <trigger-type>-<trigger-name>
> Where:
> 	* <trigger_type>, specifies the interrupt source (e.g: hrtimer)
> 	* <trigger-name>, specifies the IIO device trigger name
>
> Failing to follow this convention will result in an directory creation error.
>
> E.g, assuming that hrtimer trigger type is registered with IIO software
> trigger core:
>
> $ mkdir /config/iio/triggers/hrtimer-instance1
>

Nice, short and clean. Looks pretty good. It's a bit of a shame that we 
can't have a per type directory, but if that's how configfs works I guess 
there is not much choice.

[...]
> +static struct config_group *trigger_make_group(struct config_group *group,
> +					       const char *name)
> +{
> +	char *type_name;
> +	char *trigger_name;
> +	char buf[MAX_NAME_LEN];
> +	struct iio_sw_trigger *t;
> +
> +	snprintf(buf, MAX_NAME_LEN, "%s", name);
> +
> +	/* group name should have the form <trigger-type>-<trigger-name> */
> +	type_name = buf;
> +	trigger_name = strchr(buf, '-');
> +	if (!trigger_name) {
> +		pr_err("Unable to locate '-' in %s. Use <type>-<name>.\n", buf);

Do we want to print this side channel message? Makes it pretty easy to spam 
the kernel log with a rouge application.

> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	/* replace - with \0, this nicely separates the two strings */
> +	*trigger_name = '\0';
> +	trigger_name++;
> +
> +	t = iio_sw_trigger_create(type_name, trigger_name);
> +	if (IS_ERR(t))
> +		return ERR_CAST(t);
> +
> +	config_item_set_name(&t->group.cg_item, name);
> +
> +	return &t->group;
> +}
> +
> +static void trigger_drop_group(struct config_group *group,
> +			       struct config_item *item)
> +{
> +	struct iio_sw_trigger *t = to_iio_sw_trigger(item);
> +
> +	if (t)

t will never be NULL.

> +		iio_sw_trigger_destroy(t);
> +	config_item_put(item);
> +}

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