Re: [libgpiod][PATCH] treewide: rework struct gpiod_line_bulk

From: Bartosz Golaszewski <brgl@bgdev.pl>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Kent Gibson <warthog618@gmail.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Jack Winch <sunt.un.morcov@gmail.com>,
	Helmut Grohne <helmut.grohne@intenta.de>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>
Subject: Re: [libgpiod][PATCH] treewide: rework struct gpiod_line_bulk
Date: Fri, 23 Oct 2020 13:38:49 +0200	[thread overview]
Message-ID: <CAMRc=McD7jtBQ_CPV26Pzr63T6-o_aPpYt_CT-48H_mGuhxrGw@mail.gmail.com> (raw)
In-Reply-To: <CAHp75VeiGSJO5XnpQLMs=0nT=otVjC1tOsR7xp1gJ3tLHwUTaA@mail.gmail.com>

On Fri, Oct 23, 2020 at 12:24 PM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
>
> On Fri, Oct 23, 2020 at 12:31 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> >

[snip]

>
> > +struct gpiod_line_bulk {
> > +       struct gpiod_chip *owner;
> > +       unsigned int num_lines;
> > +       unsigned int max_lines;
> > +       struct gpiod_line *lines[1];
>
> Why not '[]' as we do in the kernel?
>

Because I want to be able to store a single line in this structure if I do:

    struct gpiod_line_bulk bulk;

Using [] makes the size of this structure not take into account the
last array member.

> > +};
>
> > +#define BULK_SINGLE_LINE_INIT(line) \
> > +               { gpiod_line_get_chip(line), 1, 1, { (line) } }
>
> Hmm... Perhaps union can help here?
>
> union {
>   struct *lines[];
>   struct *line;
> }
>
> num_lines == 1 exactly defines this.
>

Nope because gcc will scream:

error: flexible array member in union

Bartosz