linux-kernel - Re: [PATCH v3 12/13] gpiolib: add new ioctl() for monitoring changes in line info

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Date:   Tue, 24 Dec 2019 13:08:41 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Kent Gibson <warthog618@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v3 12/13] gpiolib: add new ioctl() for monitoring changes
 in line info

czw., 19 gru 2019 o 19:17 Andy Shevchenko <andy.shevchenko@...il.com>
napisał(a):
>
> On Thu, Dec 19, 2019 at 7:17 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> >
> > From: Bartosz Golaszewski <bgolaszewski@...libre.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.
>
> > -       } else if (cmd == GPIO_GET_LINEINFO_IOCTL) {
> > +       } else if (cmd == GPIO_GET_LINEINFO_IOCTL ||
> > +                  cmd == GPIO_GET_LINEINFO_WATCH_IOCTL) {
>
> Wouldn't be better for maintenance to have them separated from the day 1?
>

I think this would lead to a lot of code duplication. I left it as it is is v4.

Bart