Re: [PATCH v2 4/4] hwmon: iio: add label for channels read by iio_hwmon

[Quentin Schulz]

On 15/07/2016 16:03, Guenter Roeck wrote:
> On 07/15/2016 02:59 AM, Quentin Schulz wrote:
[...]
>> +static ssize_t iio_hwmon_read_label(struct device *dev,
>> +                    struct device_attribute *attr,
>> +                    char *buf)
>> +{
>> +    struct sensor_device_attribute *sattr = to_sensor_dev_attr(attr);
>> +    struct iio_hwmon_state *state = dev_get_drvdata(dev);
>> +    const char *label =
>> state->channels[sattr->index].channel->extend_name;
>> +
>> +    if (label)
>> +        return sprintf(buf, "%s\n", label);
>> +
> Can the name disappear on the fly, or be changed on the fly ?
> Then this is unusable. We should and can only provide labels
> if a name exists and is permanent. Otherwise all we do is
> to confuse user space.

It cannot, the extend_name field is const char* in the struct:
http://lxr.free-electrons.com/source/include/linux/iio/iio.h#L247

[...]
>> @@ -107,6 +123,18 @@ static int iio_hwmon_probe(struct platform_device
>> *pdev)
>>           }
>>
>>           sysfs_attr_init(&a->dev_attr.attr);
>> +
>> +        b = NULL;
>> +        if (st->channels[i].channel->extend_name) {
>> +            b = devm_kzalloc(dev, sizeof(*b), GFP_KERNEL);
>> +            if (b == NULL) {
>> +                ret = -ENOMEM;
>> +                goto error_release_channels;
>> +            }
>> +
>> +            sysfs_attr_init(&b->dev_attr.attr);
> 
> Why is this initialization here and not with the rest of the initialization
> of this attribute ?

I don't get your question. I've followed the exact same pattern as for
"a" variable's initialization.
The initialization is before the switch case because the name of the
exposed sysfs file depends on the type of the IIO channel. If I move the
initialization in the switch case, I'll have duplicated code.

>> +        }
>> +
>>           ret = iio_get_channel_type(&st->channels[i], &type);
>>           if (ret < 0)
>>               goto error_release_channels;
>> @@ -115,35 +143,66 @@ static int iio_hwmon_probe(struct
>> platform_device *pdev)
>>           case IIO_VOLTAGE:
>>               a->dev_attr.attr.name = kasprintf(GFP_KERNEL,
>>                                 "in%d_input",
>> -                              in_i++);
>> +                              in_i);
>> +            if (b)
>> +                b->dev_attr.attr.name = kasprintf(GFP_KERNEL,
>> +                                  "in%d_label",
>> +                                  in_i);
>> +            in_i++;
>>               break;
>>           case IIO_TEMP:
>>               a->dev_attr.attr.name = kasprintf(GFP_KERNEL,
>>                                 "temp%d_input",
>> -                              temp_i++);
>> +                              temp_i);
>> +
>> +            if (b)
>> +                b->dev_attr.attr.name = kasprintf(GFP_KERNEL,
>> +                                  "temp%d_label",
>> +                                  temp_i);
>> +            temp_i++;
>>               break;
>>           case IIO_CURRENT:
>>               a->dev_attr.attr.name = kasprintf(GFP_KERNEL,
>>                                 "curr%d_input",
>> -                              curr_i++);
>> +                              curr_i);
>> +
>> +            if (b)
>> +                b->dev_attr.attr.name = kasprintf(GFP_KERNEL,
>> +                                  "curr%d_label",
>> +                                  curr_i);
>> +            curr_i++;
>>               break;
>>           case IIO_HUMIDITYRELATIVE:
>>               a->dev_attr.attr.name = kasprintf(GFP_KERNEL,
>>                                 "humidity%d_input",
>> -                              humidity_i++);
>> +                              humidity_i);
>> +
>> +            if (b)
>> +                b->dev_attr.attr.name = kasprintf(GFP_KERNEL,
>> +                                  "humidity%d_label",
>> +                                  humidity_i);
>> +            humidity_i++;
>>               break;
>>           default:
>>               ret = -EINVAL;
>>               goto error_release_channels;
>>           }
>> -        if (a->dev_attr.attr.name == NULL) {
>> +        if (a->dev_attr.attr.name == NULL ||
>> +            (b && b->dev_attr.attr.name == NULL)) {
>>               ret = -ENOMEM;
>>               goto error_release_channels;
>>           }
> 
> Just realized that we have a memory leak here. The 'name' memory is
> never released.
> 

I don't know if we have to do something to revert the effects of
sysfs_attr_init but you sure are right that the a and b's attribute's
name is never freed. This case would be handled with devm_kasprintf, I
guess? Thanks.

>>           a->dev_attr.show = iio_hwmon_read_val;
>>           a->dev_attr.attr.mode = S_IRUGO;
>>           a->index = i;
>> -        st->attrs[i] = &a->dev_attr.attr;
>> +        st->attrs[j++] = &a->dev_attr.attr;
>> +
>> +        if (b) {
>> +            b->dev_attr.show = iio_hwmon_read_label;
>> +            b->dev_attr.attr.mode = S_IRUGO;
>> +            b->index = i;
>> +            st->attrs[j++] = &b->dev_attr.attr;
>> +        }
>>       }
>>
>>       st->attr_group.attrs = st->attrs;
>>
> 

Quentin