linux-kernel - Re: [PATCH v3 06/11] iio: core: merge buffer/ & scan

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Date:   Thu, 4 Feb 2021 15:41:37 +0200
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Alexandru Ardelean <alexandru.ardelean@...log.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Nuno Sá <nuno.sa@...log.com>,
        "Bogdan, Dragos" <dragos.bogdan@...log.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v3 06/11] iio: core: merge buffer/ & scan_elements/ attributes

On Wed, Feb 3, 2021 at 12:04 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Mon, Feb 1, 2021 at 5:28 PM Alexandru Ardelean
> <alexandru.ardelean@...log.com> wrote:
> >
> > With this change, we create a new directory for the IIO device called
> > buffer0, under which both the old buffer/ and scan_elements/ are stored.
> >
> > This is done to simplify the addition of multiple IIO buffers per IIO
> > device. Otherwise we would need to add a bufferX/ and scan_elementsX/
> > directory for each IIO buffer.
> > With the current way of storing attribute groups, we can't have directories
> > stored under each other (i.e. scan_elements/ under buffer/), so the best
> > approach moving forward is to merge their attributes.
> >
> > The old/legacy buffer/ & scan_elements/ groups are not stored on the opaque
> > IIO device object. This way the IIO buffer can have just a single
> > attribute_group object, saving a bit of memory when adding multiple IIO
> > buffers.
>
> ...
>
> > +static int iio_buffer_register_legacy_sysfs_groups(struct iio_dev *indio_dev,
> > +                                                  struct attribute **buffer_attrs,
> > +                                                  int buffer_attrcount,
> > +                                                  int scan_el_attrcount)
> > +{
> > +       struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> > +       struct attribute_group *group;
> > +       int ret;
> > +
> > +       group = &iio_dev_opaque->legacy_buffer_group;
>
> > +       group->attrs = kcalloc(buffer_attrcount + 1,
> > +                              sizeof(struct attribute *), GFP_KERNEL);
> > +       if (!group->attrs)
> > +               return -ENOMEM;
> > +
> > +       memcpy(group->attrs, buffer_attrs,
> > +              buffer_attrcount * sizeof(struct attribute *));
>
> kmemdup() ?
> Perhaps introduce kmemdup_array().

doesn't add much benefit from what i can tell;
and it complicates things with the fact that we need to add the extra
null terminator element;
[1] if we kmemdup(buffer_attrcount + 1) , the copy an extra element we
don't need, which needs to be null-ed

>
> > +       group->name = "buffer";
> > +
> > +       ret = iio_device_register_sysfs_group(indio_dev, group);
> > +       if (ret)
> > +               goto error_free_buffer_attrs;
> > +
> > +       group = &iio_dev_opaque->legacy_scan_el_group;
>
> > +       group->attrs = kcalloc(scan_el_attrcount + 1,
> > +                              sizeof(struct attribute *), GFP_KERNEL);
> > +       if (!group->attrs) {
> > +               ret = -ENOMEM;
> > +               goto error_free_buffer_attrs;
> > +       }
> > +
> > +       memcpy(group->attrs, &buffer_attrs[buffer_attrcount],
> > +              scan_el_attrcount * sizeof(struct attribute *));
>
> Ditto.

continuing from [1]
here it may be worse, because kmemdup() would copy 1 element from
undefined memory;

>
> > +       group->name = "scan_elements";
> > +
> > +       ret = iio_device_register_sysfs_group(indio_dev, group);
> > +       if (ret)
> > +               goto error_free_scan_el_attrs;
> > +
> > +       return 0;
> > +
> > +error_free_buffer_attrs:
> > +       kfree(iio_dev_opaque->legacy_buffer_group.attrs);
> > +error_free_scan_el_attrs:
> > +       kfree(iio_dev_opaque->legacy_scan_el_group.attrs);
> > +
> > +       return ret;
> > +}
>
> --
> With Best Regards,
> Andy Shevchenko