[lxc-devel] [PATCH] add lxc.network.script(.pre|.post|) configuration hooks

[Michael Tokarev]

Stefan Tomanek wrote:
> Dies schrieb Daniel Lezcano (daniel.lezcano at free.fr):
> 
>> Are we sure, we want to add these hooks (pre and post) ? I am not 
>> against adding them, but IMO it is more sane to add them if needed 
>> rather than adding something which may not be used.
> 
> Well, until now, there was not a single hook, although I desperately
> needed one. And there are probably people out there who might use
> these hooks and are not able to add them for themselves.
> 
>> Wouldn't preferable to have these two hooks:
>>
>>      lxc.network.script.up
>>      lxc.network.script.down
>>
>> (script parameter will need 'name', 'conf section' 'up' | 'down' ...
> 
> I still advise to split the hooks into generic ones and those specific
> to the network type. The parameters passed to a script configuring a veth
> device will be completely different than those passed to a macvlan device;
> generic commands can then be placed in a different script, while special
> commands can be handled in specific scripts.

Note that the script may receive other parameters, depending on the
type of the network device, just the first 3 are fixed.  THere's also
$ENVIRONMENT $VARIABLES for us.

> I'd at least propose to use two hooks for setting up the interface, on being called
> in instanciate_* (.up?), passing the arguments suitable to that network type, as well as
> one generic (.post-up?)

If there's a need, the "specific" script may call some common
code/script by its own, or the reverse.  There's no need to do
that in lxc.  Of if we do, how about adding a _set_ of scripts
for each "stage" ?  :)

>> If there is a need for a pre or post hook, we can easily add later:
> 
> Sure, _we_ probably can, but not the person who might need the patch. There are quite
> many sysadmins who are masters at shell scripting, but are unable to add such a hook
> to a C codebase. Not being able to extend the system in an easy fashion would be a huge
> show stopper for them, just as the lack of scripting was to me.

There IS a trivial way to extend system already (when
just ONE hook is implemented) - chain your scripts.
There's no need to re-implement shell in lxc.

/mjt