[systemd-devel] Supporting ExecStartPre= and friends in `systemctl set-property` or `systemd-run -p`

[Ivan Shapovalov]

On 2015-05-06 at 09:16 +0300, Andrei Borzenkov wrote:
> On Wed, May 6, 2015 at 5:52 AM, Ivan Shapovalov <intelfx100 at gmail.com
> > wrote:
> > On 2015-04-24 at 11:10 +0200, Lennart Poettering wrote:
> > > On Fri, 24.04.15 04:07, Ivan Shapovalov (intelfx100 at gmail.com) 
> > > wrote:
> > > 
> > > > - do `systemd-run` twice and somehow set up the dependencies
> > > > between
> > > >   two transient units
> > > 
> > > I'd be happy to take a patch that allows configuring deps for
> > > transient units when constructing them.
> > 
> > Hi Lennart,
> > 
> > I've just done this (also added manager-side support for
> > JoinsNamespaceOf= and RequiresMountsFor=, while at it). However, 
> > this
> > turned out to be insufficient for my usecase.
> > 
> > I have to start two transient services, say, A.service and 
> > B.service,
> > and
> > 
> > - B.service "needs" A.service
> >   (i. e. B.service Requires=A.service and After=A.service)
> > 
> > - A.service must be stopped as soon as B.service exits
> >   (i. e. A.service BindsTo=B.service)
> > 
> > And there is a contradiction: I can't make a dependency on an
> > inexistent unit.
> > If I create A.service before B.service, I can't set BindsTo=, and 
> > if I
> > create B.service before A.service, I can't set Requires= and 
> > After=.
> > 
> > Locally, I've solved this by allowing inverse dependencies to be 
> > set
> > over the bus. That is, I make B.service BoundBy=A.service. Is this
> > acceptable for upstream?
> > 
> 
> What about adding option --define-only (I do not care about actual
> name) that adds unit definition but does not start unit? Then you can
> define any number of transient units and then "systemctl start" them
> later.

I'm unsure how to fit this into the GC logic. Transient units get
unloaded (and hence removed from disk) once they become inactive.

If we create a transient unit without starting it at the same time
(before the GC has a chance to run), it will be immediately removed.

-- 
Ivan Shapovalov / intelfx /
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