Re: [PATCH v2] leds: Introduce userspace leds driver

[Jacek Anaszewski]

Hi David,

On 09/15/2016 05:25 PM, David Lechner wrote:
> On 09/15/2016 09:54 AM, Jacek Anaszewski wrote:
> > Hi Pavel,
> >
> > On 09/15/2016 03:01 PM, Pavel Machek wrote:
> > > Hi!
> > >
> > > > > @@ -0,0 +1,23 @@
> > > > > +/*
> > > > > + * Userspace driver support for leds subsystem
> > > > > + *
> > > > > + * This program is free software; you can redistribute it and/or
> > > > > modify
> > > > > + * it under the terms of the GNU General Public License as
> > > > > published by
> > > > > + * the Free Software Foundation; either version 2 of the License, or
> > > > > + * (at your option) any later version.
> > > > > + *
> > > > > + * This program is distributed in the hope that it will be useful,
> > > > > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > > > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > > > > + * GNU General Public License for more details.
> > > > > + */
> > > > > +#ifndef _UAPI__ULEDS_H_
> > > > > +#define _UAPI__ULEDS_H_
> > > > > +
> > > > > +#define ULEDS_MAX_NAME_SIZE    80
> > > > > +
> > > > > +struct uleds_user_dev {
> > > > > +    char name[ULEDS_MAX_NAME_SIZE];
> > > > > +};
> > >
> > > We already have path component length limit somewhere, right? Just use
> > > it?
> > >
> > > (And is struct with char array good idea at all? Perphaps it can just
> > > use write() length up to something reasonable, and not bother with new
> > > header file for userspace?)
> >
> > In fact in this case the addition of another public header can be
> > avoided.
>
> The main reason I did it this way is in case someone wants to extend
> this to also, for example, set the max_brightness value. If we use an
> arbitrary size string, we could never add max_brightness without
> breaking userspace.
>
> If we are sure we will never want to pass any other parameters other
> than name, then we can do away with the struct.

This is sound argument. Let's limit the name size to 64, as in case
of name variable in led_classdev_register(). This patch could also
add include directive "#include <uapi/leds/uleds.h>" to
drivers/leds/led-class.c and replace 64 with a new LED_MAX_NAME_LEN 
macro defined in the uleds.h header.

--
Best regards,
Jacek Anaszewski