Re: [PATCH 2/2] iio: core: Add "extended_name" attribute to all channels

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 10 Jun 2021 15:49:58 +0100
Paul Cercueil <paul@crapouillou.net> wrote:

> Le jeu., juin 10 2021 at 15:34:25 +0100, Jonathan Cameron 
> <Jonathan.Cameron@Huawei.com> a écrit :
> > On Thu, 10 Jun 2021 13:45:56 +0100
> > Paul Cercueil <paul@crapouillou.net> wrote:
> >   
> >>  The point of this new attribute is to make the IIO tree actually
> >>  parsable.
> >> 
> >>  Before, given this attribute as a filename:
> >>  in_voltage0_aux_sample_rate
> >> 
> >>  Userspace had no way to know if the attribute name was
> >>  "aux_sample_rate" with no extended name, or "sample_rate" with 
> >> "aux" as
> >>  the extended name, or just "rate" with "aux_sample" as the extended
> >>  name.
> >> 
> >>  This was somewhat possible to deduce when there was more than one
> >>  attribute present for a given channel, e.g:
> >>  in_voltage0_aux_sample_rate
> >>  in_voltage0_aux_frequency
> >> 
> >>  There, it was possible to deduce that "aux" was the extended name. 
> >> But
> >>  even with more than one attribute, this wasn't very robust, as two
> >>  attributes starting with the same prefix (e.g. "sample_rate" and
> >>  "sample_size") would result in the first part of the prefix being
> >>  interpreted as being part of the extended name.
> >> 
> >>  To address this issue, add an "extended_name" attribute to all 
> >> channels
> >>  that actually do have an extended name.  
> > 
> > Change the patch title to make it clear that it only applies to those
> > that have extended_name set.
> >   
> >>  For this attribute, the extended
> >>  name is not present in the filename; so in this example, the file 
> >> name
> >>  would be "in_voltage0_extended_name", and reading it would return 
> >> "aux".  
> > 
> > Ah. Now I see the slightly issue with my immediate thought that we 
> > should
> > just put this in the label attribute (and not allow both extended_name
> > and label to be provided).  
> 
> Are there cases where extended_name and label are both used?

Not yet and if we add a check as part of your series we can stop it
happening in future.  Simple checking for the read_label callback
should be enough.

> 
> If they are exclusive, then it would be fine to put it in the label 
> attribute. Parsing would be a bit more awkward because of the extended 
> name but still possible (e.g. libiio would read 'in_voltage0_foo_label' 
> and check that it returns 'foo').

That would be great!

Jonathan

> 
> -Paul
> 
> > Hmm. It's a bit ugly but given it hopefully doesn't effect that many 
> > drivers
> > I could probably live with it.
> > 
> > However, needs a patch to Documentation/ABI/testing/sysfs-bus-iio
> > and a clear statement that this is for backwards compatibility 
> > reasons.
> > I don't want to see extended_name getting added to new drivers!
> > 
> > Jonathan
> >   
> >> 
> >>  Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> >>  ---
> >>   drivers/iio/industrialio-core.c | 41 
> >> +++++++++++++++++++++++++++++++++
> >>   1 file changed, 41 insertions(+)
> >> 
> >>  diff --git a/drivers/iio/industrialio-core.c 
> >> b/drivers/iio/industrialio-core.c
> >>  index ec34d930920c..4cdf9f092d73 100644
> >>  --- a/drivers/iio/industrialio-core.c
> >>  +++ b/drivers/iio/industrialio-core.c
> >>  @@ -723,6 +723,16 @@ static ssize_t iio_read_channel_label(struct 
> >> device *dev,
> >>   	return indio_dev->info->read_label(indio_dev, this_attr->c, buf);
> >>   }
> >> 
> >>  +static ssize_t iio_read_channel_extended_name(struct device *dev,
> >>  +					      struct device_attribute *attr,
> >>  +					      char *buf)
> >>  +{
> >>  +	const struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
> >>  +	const struct iio_chan_spec *chan = this_attr->c;
> >>  +
> >>  +	return sprintf(buf, "%s\n", chan->extend_name);
> >>  +}
> >>  +
> >>   static ssize_t iio_read_channel_info(struct device *dev,
> >>   				     struct device_attribute *attr,
> >>   				     char *buf)
> >>  @@ -1185,6 +1195,32 @@ static int 
> >> iio_device_add_channel_label(struct iio_dev *indio_dev,
> >>   	return 1;
> >>   }
> >> 
> >>  +static int
> >>  +iio_device_add_channel_extended_name(struct iio_dev *indio_dev,
> >>  +				     struct iio_chan_spec const *chan)
> >>  +{
> >>  +	struct iio_dev_opaque *iio_dev_opaque = 
> >> to_iio_dev_opaque(indio_dev);
> >>  +	int ret;
> >>  +
> >>  +	if (!chan->extend_name)
> >>  +		return 0;
> >>  +
> >>  +	ret = __iio_add_chan_devattr("extended_name",
> >>  +				     chan,
> >>  +				     &iio_read_channel_extended_name,
> >>  +				     NULL,
> >>  +				     0,
> >>  +				     IIO_SEPARATE,
> >>  +				     &indio_dev->dev,
> >>  +				     NULL,
> >>  +				     &iio_dev_opaque->channel_attr_list,
> >>  +				     false);
> >>  +	if (ret < 0)
> >>  +		return ret;
> >>  +
> >>  +	return 1;
> >>  +}
> >>  +
> >>   static int iio_device_add_info_mask_type(struct iio_dev *indio_dev,
> >>   					 struct iio_chan_spec const *chan,
> >>   					 enum iio_shared_by shared_by,
> >>  @@ -1327,6 +1363,11 @@ static int 
> >> iio_device_add_channel_sysfs(struct iio_dev *indio_dev,
> >>   		return ret;
> >>   	attrcount += ret;
> >> 
> >>  +	ret = iio_device_add_channel_extended_name(indio_dev, chan);
> >>  +	if (ret < 0)
> >>  +		return ret;
> >>  +	attrcount += ret;
> >>  +
> >>   	if (chan->ext_info) {
> >>   		unsigned int i = 0;
> >>   		for (ext_info = chan->ext_info; ext_info->name; ext_info++) {  
> >   
> 
>