Re: [PATCH v2 2/2] iio: core: Support reading extended name as label

[Paul Cercueil]

Hi Alexandru,

Le jeu., juin 17 2021 at 10:22:35 +0300, Alexandru Ardelean 
<ardeleanalex@xxxxxxxxx> a écrit :
> On Wed, Jun 16, 2021 at 7:00 PM Paul Cercueil <paul@xxxxxxxxxxxxxxx> 
> wrote:
> >  The point of this new change 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 the issue, knowing that channels will never have both a 
> > label
> >  and an extended name, set the channel's label to the extended name.
> >  In this case, the label's attribute will also have the extended 
> > name in
> >  its filename, but we can live with that - userspace can open
> >  in_voltage0_<prefix>_label and verify that it returns <prefix> to 
> > obtain
> >  the extended name.
>
> The best way would have been for all drivers [using extend_name] to
> implement their own read_label hook.

Let's agree to disagree :)

> But this can work fine as well [as the other method would add some 
> duplication].
>
> >  Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> >  ---
> >   drivers/iio/industrialio-core.c | 10 +++++++---
> >   1 file changed, 7 insertions(+), 3 deletions(-)
> >
> >  diff --git a/drivers/iio/industrialio-core.c 
> > b/drivers/iio/industrialio-core.c
> >  index 81f40dab778a..9b37e96538c2 100644
> >  --- a/drivers/iio/industrialio-core.c
> >  +++ b/drivers/iio/industrialio-core.c
> >  @@ -717,8 +717,12 @@ static ssize_t iio_read_channel_label(struct 
> > device *dev,
> >          struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> >          struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
> >
> >  -       if (!indio_dev->info->read_label)
> >  -               return -EINVAL;
> >  +       if (!indio_dev->info->read_label) {
> >  +               if (this_attr->c->extend_name)
> >  +                       return sprintf(buf, "%s\n", 
> > this_attr->c->extend_name);
> >  +               else
>
> nitpick: else statement has no effect
>
> well, this block could be reworked a bit as:
>
> ----------------------------------------------------
> if (indio_dev->info->read_label)
>    return indio_dev->info->read_label(indio_dev, this_attr->c, buf);
>
> if (this_attr->c->extend_name)
>     return sprintf(buf, "%s\n", this_attr->c->extend_name);
>
> return -EINVAL;
> ----------------------------------------------------

I generally prefer to make the diff as small as possible so that the 
changes are more obvious. But this does look better.

-Paul

> >  +                       return -EINVAL;
> >  +       }
> >
> >          return indio_dev->info->read_label(indio_dev, this_attr->c, 
> > buf);
> >   }
> >  @@ -1160,7 +1164,7 @@ static int 
> > iio_device_add_channel_label(struct iio_dev *indio_dev,
> >          struct iio_dev_opaque *iio_dev_opaque = 
> > to_iio_dev_opaque(indio_dev);
> >          int ret;
> >
> >  -       if (!indio_dev->info->read_label)
> >  +       if (!indio_dev->info->read_label && !chan->extend_name)
> >                  return 0;
> >
> >          ret = __iio_add_chan_devattr("label",
> >  --
> >  2.30.2