Re: [PATCH 10/11] iio: buffer: Make length attribute read only for buffers without set_length

[Jonathan Cameron <jic23@kernel.org>]

On 26/11/14 17:55, Lars-Peter Clausen wrote:
> If a buffer implementation does not implement the set_length() callback the
> length will be static and can not be changed by userspace. Mark the length
> attribute as a read only property in this case so userspace is aware of this
> rather than just silently accepting any length value.
> 
> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Nice little change.

Thanks
Jonathan
> ---
>  drivers/iio/industrialio-buffer.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index a4d3ff6..3e0c3a9 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> @@ -416,8 +416,7 @@ static ssize_t iio_buffer_write_length(struct device *dev,
>  	if (iio_buffer_is_active(indio_dev->buffer)) {
>  		ret = -EBUSY;
>  	} else {
> -		if (buffer->access->set_length)
> -			buffer->access->set_length(buffer, val);
> +		buffer->access->set_length(buffer, val);
>  		ret = 0;
>  	}
>  	mutex_unlock(&indio_dev->mlock);
> @@ -755,6 +754,8 @@ static const char * const iio_scan_elements_group_name = "scan_elements";
>  
>  static DEVICE_ATTR(length, S_IRUGO | S_IWUSR, iio_buffer_read_length,
>  	iio_buffer_write_length);
> +static struct device_attribute dev_attr_length_ro = __ATTR(length,
> +	S_IRUGO, iio_buffer_read_length, NULL);
>  static DEVICE_ATTR(enable, S_IRUGO | S_IWUSR,
>  	iio_buffer_show_enable, iio_buffer_store_enable);
>  
> @@ -781,7 +782,10 @@ int iio_buffer_alloc_sysfs(struct iio_dev *indio_dev)
>  	if (!buffer->buffer_group.attrs)
>  		return -ENOMEM;
>  
> -	buffer->buffer_group.attrs[0] = &dev_attr_length.attr;
> +	if (buffer->access->set_length)
> +		buffer->buffer_group.attrs[0] = &dev_attr_length.attr;
> +	else
> +		buffer->buffer_group.attrs[0] = &dev_attr_length_ro.attr;
>  	buffer->buffer_group.attrs[1] = &dev_attr_enable.attr;
>  	if (buffer->attrs)
>  		memcpy(&buffer->buffer_group.attrs[2], buffer->attrs,
>