linux-kernel - Re: [PATCH v4 07/20] gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL and GPIO_V2_LINE_GET_VALUES

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Message-ID: <CAMpxmJVMJYJ71z59Mu-mCTQPNqV9N9sXJXNBjYazGo0tmXthfg@mail.gmail.com>
Date:   Sat, 15 Aug 2020 09:21:22 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Kent Gibson <warthog618@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v4 07/20] gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL
 and GPIO_V2_LINE_GET_VALUES_IOCTL

On Sat, Aug 15, 2020 at 8:53 AM Kent Gibson <warthog618@...il.com> wrote:
>
> On Fri, Aug 14, 2020 at 09:31:29PM +0200, Bartosz Golaszewski wrote:
> > On Fri, Aug 14, 2020 at 5:04 AM Kent Gibson <warthog618@...il.com> wrote:
> > >
> > > Add support for requesting lines using the GPIO_V2_GET_LINE_IOCTL, and
> > > returning their current values using GPIO_V2_LINE_GET_VALUES_IOCTL.
> > >
> > > Signed-off-by: Kent Gibson <warthog618@...il.com>
> > > ---
> >
> > Hi Kent,
> >
> > not many comments here, just a couple minor details below.
> >
>
> [snip]
>
> > > +
> > > +/**
> > > + * struct line - contains the state of a userspace line request
> > > + * @gdev: the GPIO device the line request pertains to
> > > + * @label: consumer label used to tag descriptors
> > > + * @num_descs: the number of descriptors held in the descs array
> > > + * @descs: the GPIO descriptors held by this line request, with @num_descs
> > > + * elements.
> > > + */
> > > +struct line {
> >
> > How about line_request, line_request_data or line_req_ctx? Something
> > more intuitive than struct line that doesn't even refer to a single
> > line. Same for relevant functions below.
> >
>
> As I've mentioned previously, I'm not a fan of names that include _data,
> _ctx, _state, or similar that don't really add anything.
>

I certainly disagree with you on this. I think it's useful to discern
the object itself from data associated with it. Let's consider struct
irq_data and let's imagine it would be called struct irq instead. The
latter would be misleading - as this struct contains a lot additional
fields that form the context for the irq but aren't logically part of
the "irq object". And then you have irq_common_data which is even more
disconnected from the irq. This also would make using the name "irq"
for the variables containing the global irq number confusing.

I think the same happens here: we may want to use the name "line" for
local variables and then having "struct line_data" (or similar) would
make it easier to read.

I'll listen to other's suggestions/voices but personally I think that
_ctx, _data etc. suffixes actually make sense.

> I did consider line_request, but that was too close to the
> gpio_v2_line_request in gpio.d, not just the struct but also the
> resulting local variables, particularly in line_create() where they
> co-exist.
>
> Given the ioctl names, GPIO_V2_GET_LINE_IOCTL and
> GPIO_V2_LINE_GET/SET_xxx, that all create or operate on this struct, and
> that this is within the scope of gpiolib-cdev, the name 'line' seemed the
> best fit.
>

And that's why line_data or line_request_data do make sense IMO.

> And how does it not refer to a single line - what are the descs??
>

I meant the fact that it can refer to multiple lines while being
called "struct line". I do find this misleading.

Bart

> No problems with your other comments.
>
> Cheers,
> Kent.
>