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

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Message-ID: <20190902190843.GB25019@kroah.com>
Date:   Mon, 2 Sep 2019 21:08:43 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Akinobu Mita <akinobu.mita@...il.com>, linux-leds@...r.kernel.org,
        linux-kernel@...r.kernel.org, Pavel Machek <pavel@....cz>,
        Dan Murphy <dmurphy@...com>
Subject: Re: [PATCH] leds: remove PAGE_SIZE limit of
 /sys/class/leds/<led>/trigger

On Mon, Sep 02, 2019 at 08:47:02PM +0200, Jacek Anaszewski wrote:
> On 9/2/19 8:12 PM, Greg KH wrote:
> > On Sun, Sep 01, 2019 at 06:53:34PM +0200, Jacek Anaszewski wrote:
> >> Hi Akinobu,
> >>
> >> Thank you for the patch.
> >>
> >> I have one nit below but in general it looks good to me.
> >> I've tested it with 2000 mtd triggers (~14kB file size)
> >> and it worked flawlessly.
> >>
> >> Still, I would like to have ack from Greg for it.
> >>
> >> Adding Greg on Cc.
> >>
> >> On 8/29/19 4:49 PM, 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.
> > 
> > But this is NOT a binary file.  A sysfs binary file is used for when the
> > kernel passes data to or from hardware without any parsing of the data
> > by the kernel.
> > 
> > You are not doing that here, you are abusing the "one value per file"
> > rule of sysfs so much that you are forced to work around the limitation
> > it put in place on purpose to keep you from doing stuff like this.
> > 
> > Please fix this "correctly" by creating a new api that works properly
> > and just live with the fact that this file will never work correctly and
> > move everyone to use the new api instead.
> > 
> > Don't keep on abusing the interface by workarounds like this, it is not
> > ok.
> 
> In the message [0] you pledged to give us exception for that, provided
> it will be properly documented in the code. I suppose you now object
> because the patch does not meet that condition.

Well, I honestly don't remember writing that email, but it was 5 months
and many thousands of emails ago :)

Also, you all didn't document the heck out of this.  So no, I really do
not want to see this patch accepted as-is.

> Provided that will be fixed, can we count on your ack for the
> implementation of the solution you proposed? :-)

Let's see the patch that actually implements what I suggested first :)

thanks,

greg k-h