linux-kernel - Re: [PATCH v1] leds: trigger: pattern: notify userpace if pattern finished

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Date:   Fri, 2 Sep 2022 01:43:45 +0300
From:   Dmitry Rokosov <ddrokosov@...rdevices.ru>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Martin Kurbanov <mmkurbanov@...rdevices.ru>,
        Pavel Machek <pavel@....cz>,
        Raphael Teysseyre <rteysseyre@...il.com>,
        Baolin Wang <baolin.wang@...aro.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel <kernel@...rdevices.ru>
Subject: Re: [PATCH v1] leds: trigger: pattern: notify userpace if pattern
 finished

[...]

> > +static int pattern_trig_add_pattern_ended(struct led_classdev *led_cdev)
> > +{
> > +       struct pattern_trig_data *data = led_get_trigger_data(led_cdev);
> > +       struct device *dev = led_cdev->dev;
> > +       int ret;
> > +
> > +       ret = device_create_file(dev, &dev_attr_pattern_ended);
> > +       if (ret) {
> > +               dev_err(dev,
> > +                       "Error creating pattern_ended (%pe)\n", ERR_PTR(ret));
> > +               return ret;
> > +       }
> > +
> > +       data->pattern_ended = sysfs_get_dirent(dev->kobj.sd, "pattern_ended");
> > +       if (!data->pattern_ended) {
> > +               dev_err(dev, "Error getting pattern_ended kernelfs\n");
> > +               device_remove_file(dev, &dev_attr_pattern_ended);
> > +               return -ENXIO;
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static void pattern_trig_remove_pattern_ended(struct led_classdev *led_cdev)
> > +{
> > +       struct pattern_trig_data *data = led_get_trigger_data(led_cdev);
> > +
> > +       sysfs_put(data->pattern_ended);
> > +       device_remove_file(led_cdev->dev, &dev_attr_pattern_ended);
> > +}
> 
> I'm wondering if you can always have a file and instead provide a
> value there, so user space may use epoll() mechanism on that. It will
> simplify your code here.

Could you please explain what you mean? In the current implementation
userspace can use epoll() already.

-- 
Thank you,
Dmitry