Re: [PATCH v2 10/11] gpiolib: add new ioctl() for monitoring changes in line info

From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Bartosz Golaszewski <brgl@bgdev.pl>,
	Kent Gibson <warthog618@gmail.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 10/11] gpiolib: add new ioctl() for monitoring changes in line info
Date: Thu, 5 Dec 2019 10:42:14 +0100	[thread overview]
Message-ID: <CAMpxmJVXVVVMPA_hRbs3mUsFs=s_VtQK9SvvYK3Xc5X27NPTKw@mail.gmail.com> (raw)
In-Reply-To: <CAHp75VdiAtHtdrUP2EmLULh86oO37ha8si10gFKYRavXCEwRRQ@mail.gmail.com>

śr., 4 gru 2019 o 23:34 Andy Shevchenko <andy.shevchenko@gmail.com> napisał(a):
>
> On Wed, Dec 4, 2019 at 6:03 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> >
> > From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> >
> > Currently there is no way for user-space to be informed about changes
> > in status of GPIO lines e.g. when someone else requests the line or its
> > config changes. We can only periodically re-read the line-info. This
> > is fine for simple one-off user-space tools, but any daemon that provides
> > a centralized access to GPIO chips would benefit hugely from an event
> > driven line info synchronization.
> >
> > This patch adds a new ioctl() that allows user-space processes to reuse
> > the file descriptor associated with the character device for watching
> > any changes in line properties. Every such event contains the updated
> > line information.
> >
> > Currently the events are generated on three types of status changes: when
> > a line is requested, when it's released and when its config is changed.
> > The first two are self-explanatory. For the third one: this will only
> > happen when another user-space process calls the new SET_CONFIG ioctl()
> > as any changes that can happen from within the kernel (i.e.
> > set_transitory() or set_debounce()) are of no interest to user-space.
>
> > +/**
> > + * struct gpioline_info_changed - Information about a change in status
> > + * of a GPIO line
> > + * @timestamp: estimate of time of status change occurrence, in nanoseconds
> > + * @event_type: one of GPIOLINE_CHANGED_REQUESTED, GPIOLINE_CHANGED_RELEASED
> > + * and GPIOLINE_CHANGED_CONFIG
> > + * @info: updated line information
> > + */
> > +struct gpioline_info_changed {
> > +       __u64 timestamp;
> > +       __u32 event_type;
> > +       struct gpioline_info info;
> > +       __u32 padding[4]; /* for future use */
> > +};
>
> Has this been tested against 64-bit kernel / 32-bit userspace case?
>

No. Since this is a new thing - do you think it's possible to simply
arrange the fields or add padding such that the problem doesn't even
appear in the first place?

Bart