linux-kernel - Re: [PATCH 1/5] leds: remove PAGE_SIZE limit of /sys/class/leds/<led>/trigger

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Message-ID: <20190911153602.GB13865@kroah.com>
Date:   Wed, 11 Sep 2019 16:36:02 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Akinobu Mita <akinobu.mita@...il.com>
Cc:     linux-leds@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, Dan Murphy <dmurphy@...com>
Subject: Re: [PATCH 1/5] leds: remove PAGE_SIZE limit of
 /sys/class/leds/<led>/trigger

On Thu, Sep 12, 2019 at 12:25:28AM +0900, Akinobu Mita wrote:
> 2019年9月8日(日) 22:10 Greg Kroah-Hartman <gregkh@...uxfoundation.org>:
> >
> > On Sun, Sep 08, 2019 at 09:41:08PM +0900, Akinobu Mita wrote:
> > > Reading /sys/class/leds/<led>/trigger returns all available LED triggers.
> > > However, the size of this file is limited to PAGE_SIZE because of the
> > > limitation for sysfs attribute.
> > >
> > > Enabling LED CPU trigger on systems with thousands of CPUs easily hits
> > > PAGE_SIZE limit, and makes it impossible to see all available LED triggers
> > > and which trigger is currently activated.
> > >
> > > This converts /sys/class/leds/<led>/trigger to bin attribute and removes
> > > the PAGE_SIZE limitation.
> > >
> > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> > > Cc: Jacek Anaszewski <jacek.anaszewski@...il.com>
> > > Cc: Pavel Machek <pavel@....cz>
> > > Cc: Dan Murphy <dmurphy@...com>
> > > Acked-by: Pavel Machek <pavel@....cz>
> > > Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> > > ---
> > >  drivers/leds/led-class.c    |  8 ++--
> > >  drivers/leds/led-triggers.c | 90 ++++++++++++++++++++++++++++++++++-----------
> > >  drivers/leds/leds.h         |  6 +++
> > >  include/linux/leds.h        |  5 ---
> > >  4 files changed, 79 insertions(+), 30 deletions(-)
> > >
> > > diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> > > index 4793e77..8b5a1d1 100644
> > > --- a/drivers/leds/led-class.c
> > > +++ b/drivers/leds/led-class.c
> > > @@ -73,13 +73,13 @@ static ssize_t max_brightness_show(struct device *dev,
> > >  static DEVICE_ATTR_RO(max_brightness);
> > >
> > >  #ifdef CONFIG_LEDS_TRIGGERS
> > > -static DEVICE_ATTR(trigger, 0644, led_trigger_show, led_trigger_store);
> > > -static struct attribute *led_trigger_attrs[] = {
> > > -     &dev_attr_trigger.attr,
> > > +static BIN_ATTR(trigger, 0644, led_trigger_read, led_trigger_write, 0);
> >
> > BIN_ATTR_RW()?
> 
> We can use BIN_ATTR_RW() by renaming led_trigger_{read,write}() to
> trigger_{read,write}().  But led_trigger_{read,write}() are not static
> functions.  These are defined as export symbols for led-class module.
> 
> So trigger_{read,write}() will be too generic symbol names, won't they?

Yes they would, sorry I didn't notice that.

Wait, why are those functions being exported?  Who is calling a sysfs
function from a different code path than sysfs?

thanks,

greg k-h