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

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Date:   Thu, 17 Jun 2021 10:22:35 +0300
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-iio <linux-iio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] iio: core: Support reading extended name as label

On Wed, Jun 16, 2021 at 7:00 PM Paul Cercueil <paul@...pouillou.net> 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.
But this can work fine as well [as the other method would add some duplication].

> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  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;
----------------------------------------------------


> +                       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
>