On 12/06/2015 19:01, Steve Litt wrote:
> The one thing I *do* know is that we need to provide a sd_notify
> interface, even if it does nothing at all and drops passed information
> on the floor.

Please don't do this.
The more you bend to the systemd interfaces, the more it gets a foot
in the door. By implementing a dummy sd_notify, you acknowledge the
validity of the interface; you accept that the systemd people have
created something worth using, and you validate the existence of
(a part of) systemd.

The thing is, the sd_notify interface is not *too* bad, but like
the rest of systemd, it is overengineered, too complex, and mixes
several different things in a monolithic way so that people who are
trying to actually implement real support for sd_notify are bound
to reinvent systemd one way or another.

It's absolutely like the old Microsoft "embrace and extend" strategy,
you know. They get one foot in the door by providing something useful,
but then pile their own crap onto it, and people are already relying
on it, so you want to implement support for it, and then you're captive,
and the only way to be 100%-compatible is to use the original product.

  There's a much simpler mechanism that can be used to provide
readiness notification, and that I suggest in
    http://skarnet.org/software/s6/notifywhenup.html
and that is: write a given character on a descriptor, then close that
descriptor.
  It doesn't get any simpler than that, it doesn't require linking
daemons against any library, and it can be made to be compatible
with *everything*. If a daemon supports that mechanism, it is very easy
to write a systemd-notify program that would wrap that daemon and
communicate with systemd via sd_notify to inform it of the daemon's
readiness, the way s6-notifywhenup does for s6.

Please KISS, and design good interfaces to be adopted, instead of
letting yourselves get bullied by systemd forcing its interfaces down
your throats and jumping through hoops to adapt to them. With a
simpler interface and a trivial wrapper program, the influence of
systemd only extends to the wrapper program, and not to the daemons
themselves.

--
Laurent