Re: [PATCH V3] leds: trigger: Introduce an USB port trigger

From	Greg KH <gregkh@linuxfoundation.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH V3] leds: trigger: Introduce an USB port trigger
Date	2016-08-25 15:00 +0200
Message-ID	<sa2qd-14L-13@gated-at.bofh.it> (permalink)
References	<s9s3o-1C3-23@gated-at.bofh.it> <s9CFs-gj-13@gated-at.bofh.it> <s9CP7-kO-13@gated-at.bofh.it> <s9NAS-7TC-15@gated-at.bofh.it> <s9Vf3-54s-7@gated-at.bofh.it>
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On Thu, Aug 25, 2016 at 07:14:52AM +0200, Rafał Miłecki wrote:
> On 24 August 2016 at 23:04, Greg KH <gregkh@linuxfoundation.org> wrote:
> > On Wed, Aug 24, 2016 at 11:29:51AM +0200, Rafał Miłecki wrote:
> >> On 24 August 2016 at 11:22, Greg KH <gregkh@linuxfoundation.org> wrote:
> >> > On Wed, Aug 24, 2016 at 12:03:29AM +0200, Rafał Miłecki wrote:
> >> >> +static ssize_t ports_show(struct device *dev, struct device_attribute *attr,
> >> >> +                       char *buf)
> >> >> +{
> >> >> +     struct led_classdev *led_cdev = dev_get_drvdata(dev);
> >> >> +     struct usbport_trig_data *usbport_data = led_cdev->trigger_data;
> >> >> +     struct usbport_trig_port *port;
> >> >> +     ssize_t ret = 0;
> >> >> +     int len;
> >> >> +
> >> >> +     list_for_each_entry(port, &usbport_data->ports, list) {
> >> >> +             len = sprintf(buf + ret, "%s\n", port->name);
> >> >> +             if (len >= 0)
> >> >> +                     ret += len;
> >> >> +     }
> >> >> +
> >> >> +     return ret;
> >> >> +}
> >> >
> >> > sysfs is "one value per file", here you are listing a bunch of things in
> >> > one sysfs file.  Please don't do that.
> >>
> >> OK. What do you think about creating "ports" subdirectory and creating
> >> file-per-port in it? Then I'd need to bring back something like
> >> "new_port" and "remove_port". Does it sound OK?
> >
> > Maybe, I don't know.  Why is "USB" somehow unique here?  Why isn't this
> > the same for PCI slots/ports?  pccard?  sdcard?  thunderbolt?
> 
> Good question. I would like to extend this USB port trigger in the
> future by reacting to USB activity. This involves playing with URBs
> and I believe that at that point it'd be getting too much USB specific
> to /rule them all/.

Oh that's never going to work, sorry.  USB "activity" happens deep in
USB host controller hardware, not up at the kernel level at all.  It's
just too fast, and would take up too much CPU to do it otherwise.  Heck,
even old UHCI 1.1 USB controllers did this.

USB "activity" happens all the time, look at a USB bus analyzer if you
want to see what goes on.  Teasing out what is "real data" and what is
just "normal bus activity" is impossible at the kernel level, and really
makes no sense at all (your led would just be "on" all the time.)

Are you sure you know how USB works?  Writing things like this makes me
really worry...

greg k-h

Thread

[PATCH V3] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-24 00:10 +0200
  Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Greg KH <gregkh@linuxfoundation.org> - 2016-08-24 11:30 +0200
    Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-24 11:40 +0200
      Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Greg KH <gregkh@linuxfoundation.org> - 2016-08-24 23:10 +0200
        Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-25 07:20 +0200
          Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Greg KH <gregkh@linuxfoundation.org> - 2016-08-25 15:00 +0200
            Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Bjørn Mork <bjorn@mork.no> - 2016-08-25 21:00 +0200
              Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Greg KH <gregkh@linuxfoundation.org> - 2016-08-25 23:10 +0200
  Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Greg KH <gregkh@linuxfoundation.org> - 2016-08-24 11:30 +0200
    Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-24 11:30 +0200
      Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Greg KH <gregkh@linuxfoundation.org> - 2016-08-24 23:20 +0200
  Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-24 13:10 +0200
    Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Matthias Brugger <mbrugger@suse.com> - 2016-08-24 14:00 +0200
  Re: [PATCH V3] leds: trigger: Introduce an USB port trigger Matthias Brugger <mbrugger@suse.com> - 2016-08-24 13:20 +0200
  [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-24 20:00 +0200
    Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Bjørn Mork <bjorn@mork.no> - 2016-08-24 21:20 +0200
      Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-24 22:50 +0200
    Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Jacek Anaszewski <j.anaszewski@samsung.com> - 2016-08-25 10:20 +0200
      Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Matthias Brugger <mbrugger@suse.com> - 2016-08-25 10:30 +0200
      Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-25 10:40 +0200
        Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Jacek Anaszewski <j.anaszewski@samsung.com> - 2016-08-25 11:10 +0200
          Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Alan Stern <stern@rowland.harvard.edu> - 2016-08-25 16:50 +0200
            Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Jacek Anaszewski <jacek.anaszewski@gmail.com> - 2016-08-25 20:50 +0200
              Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Alan Stern <stern@rowland.harvard.edu> - 2016-08-25 21:40 +0200
                Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Alan Stern <stern@rowland.harvard.edu> - 2016-08-25 22:10 +0200
              Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-26 18:00 +0200
                Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Jacek Anaszewski <j.anaszewski@samsung.com> - 2016-08-29 10:00 +0200
                Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Pavel Machek <pavel@ucw.cz> - 2016-08-29 10:10 +0200
                Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-29 10:30 +0200
                Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Pavel Machek <pavel@ucw.cz> - 2016-08-29 10:50 +0200
                Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-29 11:10 +0200
              Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Pavel Machek <pavel@ucw.cz> - 2016-08-26 22:00 +0200
                Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Jacek Anaszewski <j.anaszewski@samsung.com> - 2016-08-29 10:40 +0200
          Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Pavel Machek <pavel@ucw.cz> - 2016-08-26 21:50 +0200
      Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger Rafał Miłecki <zajec5@gmail.com> - 2016-08-25 10:50 +0200

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