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

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Date:	Wed, 06 May 2015 19:15:27 +0300
From:	Daniel Baluta <daniel.baluta@...el.com>
To:	Lars-Peter Clausen <lars@...afoo.de>, 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 10:59 PM, Lars-Peter Clausen wrote:
> 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.

I think this is useful, people can get crazy for random -EINVAL errors 
:). Also the same is done in drivers/usb/gadget/configfs.c.


>
>> +        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.

Agree, will fix in v6.
>
>> +        iio_sw_trigger_destroy(t);
>> +    config_item_put(item);
>> +}
>
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