Re: [libgpiod] feature request: output state read and sustain

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Wed, Jun 29, 2022 at 1:20 PM Kent Gibson <warthog618@xxxxxxxxx> wrote:
> On Wed, Jun 29, 2022 at 12:58:18PM +0200, Andy Shevchenko wrote:
> > On Wed, Jun 29, 2022 at 12:48 PM Kent Gibson <warthog618@xxxxxxxxx> wrote:
> > > On Wed, Jun 29, 2022 at 12:27:13PM +0200, Andy Shevchenko wrote:
> > > > On Wed, Jun 29, 2022 at 11:27 AM Jiří Prchal <jiri.prchal@xxxxxxxxxxx> wrote:

...

> > > > Do not use shell. Use proper programming language that may give you an
> > > > easier way of handling this, i.e. _context_. Shell tools are
> > > > _context-less_ and here is the problem you are trying to solve, but
> > > > from the wrong end.
> > >
> > > Actually my proposed gpioset for v2 will support running interactively
> > > so it can maintain context and be driven from shell - for cases where
> > > basic scripting will suffice.
> >
> > Dunno if it's the right direction and if I missed any (additional) discussion.
> > As far as I remember the idea was to introduce DBus aware daemon that
> > should handle the context of the line and at the same time consider security
> > implications. Allowing shell to be context-aware is a hidden mine
> > field. What will happen if the script/user forgets to move the line to
> > the proper state and the chip will drain a lot of current? So, at
> > least PM concerns just popped up immediately to my mind. What else can
> > be problematic? So, I dunno, it's a good idea to allow shell to leave
> > a line in some state when the user actually doesn't care about it
> > anymore. At the bare minimum this mustn't be default behaviour.
>
> I don't think it is what you think it is.
> Take a look.  If you don't like it then get Bart to bin it.
>
> There was no on-list discussion.  I had preliminary disussions with Bart,
> and had intended to float it as an RFC, but got distracted by other
> things and ended up going direct to an implementation.
>
> Last I heard the DBus daemon is still on the cards, but not sure where
> Bart is with it, and the gpioset addition is for simpler cases where
> DBus is overkill or where there is no daemon.
>
> It is not the default behaviour, it is an optional mode.

Good!

> gpioset maintains the context, not shell.

A-ha, that's cool, it pleases me.

> "User's forgetting" is language independent.  Shell scripts matter!

:-)

> What else have I missed replying to? I don't know.
>
> And good to see our apparent agreement in the previous mails was just an
> aberation.  I was starting to think there was something wrong with the
> universe :-|.

Ha-ha.

-- 
With Best Regards,
Andy Shevchenko