Dependencies

[Sean E. Russell]

Hi,

I'm trying to write a compatibility layer of event scripts for Gentoo. One 
thing I can't find any documentation on is how to have a service wait until a 
set of events have been generated.  An example of mounting network 
filesystems is a good example; how would one write the rules to have, for 
example, the "netfs" process wait until it receives BOTH network/started and 
localfs/started events? 

Also, I'd like a pointer to any discussion about conditional use cases.  Is 
there any mechanism for supporting the case where a service CAN use another 
service, but doesn't require it?  This may be an difficult problem to solve 
in an indeterminate, event-driven system like Upstart, but I'd like to know 
if anybody has given it any thought.  An example of this is a printing 
subsystem, where printers are connected both locally and remotely.  In this 
case, the Cups service may be triggered when a USB printer is detected, and 
when the network comes up.  How is this to be handled?  Do we start Cups when 
it gets a USB event, and then restart it when the network comes up?


Finally, I'd like to voice a couple of opinions that I'll only comment on 
once; I won't debate them, I just want to record them.

1) Any listserve that doesn't support searching sucks.  Hard.  If a question 
is a FAQ and is answered somewhere in such a listserver, then tough luck.  It 
is not justifiable to point people at the list archives for answers, which 
renders the listserve practically useless.  I'd recommend moving this list to 
a non-crappy listserve.
 
2) If there's a FAQ, it would be a good idea to link to it, prominently, from 
the main Upstart page.  If there isn't, then I won't complain; I know the 
project is young yet.

3) The "getting started" tutorial is good, but utterly impractical for 
anything other sysinit-based systems.  I'd really like to see even a sparse, 
rough draft, but formalized syntax for the scripts, and/or some examples of 
non-trivial scripts.  For example, describing how to handle multiple event 
dependencies :-)  Since the examples provided offload all of the 
inter-service dependency handling to sysinit, they aren't very useful. 

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