non-blocking dependencies

Sven Mueller debian at incase.de
Wed Aug 17 17:19:39 UTC 2005


Henrique de Moraes Holschuh wrote on 17/08/2005 15:22:

>> On Wed, 17 Aug 2005, Troy Heber wrote:
>>
>
>>>>It's actually more complicated than that. How do you test for "up and
>>>>running"?  ifup returns when the interface is "up" but has no way to
see when
>
>>
>> You test for the functionality you need.  In this case, ip link until
it has
>> proper IPs assigned, or add a hook to DHCP directly that sets up
semasphores
>> (we will need help from the DHCP packages for this one).


Network link status as a dependency is a problem in many ways. Most
importantly because the link could go back down any second, no matter
wether it is ethernet or plip/slip/ppp or something completely
different. Also not all configured links might need to be up to fulfill
the "networking" dependency (for example if you don't need the computers
LAN connection to be available, but only its internet connection).....

Anyway: Setting a semaphore from "within" the DHCP client is easy for
dhcp-client/dhcp3-client since they provide a script which is called to
do the real setup and as far as I recall also provide hook directories
(runparts type) to hook into the setup process.


>>>>This is only one example. I think that any new initscript design
should try
>>>>to improve the dependency situation, including allowing users to
define their
>>>>own conditional dependencies. I.E. networking is not
functional/running until we can
>>>>ping the router, etc.
>
>>
>> That is something it ALREADY does (err... will do :P ).  What it does
not,
>> and should not ever bother with at the initscript subsystem level is
how to
>> implement such tests.   This belongs in the initscript level itself...


IMHO:
Any service which provides an init-script (or equivalent) also should
provide an implementation of these tests, preferably in a form easily
adjustable to local needs by the local admin.

cu,
sven


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