[libvirt] [PATCH] virsh: add custom readline generator

[Michal Privoznik]

On 27.06.2011 21:39, Eric Blake wrote:
> On 06/27/2011 12:06 PM, Michal Privoznik wrote:
>>> That is, if you have command-based custom generators, then each command
>>> has to repeat parsing functionality, then call back to common list
>>> generators; whereas if you have option-based custom generators, then you
>>> have fewer callbacks because all the smarts are tied to well-typed
>>> options, and after all, it is the type of each option that determines
>>> which list to generate, more than the type of the command that includes
>>> the option.
>>>
>> I was thinking about same feature and started to work on it during this
>> weekend. But I ran into a problem. Basically, what I intended to
>> implement, is:
>>
>> 1.) expand struct vshCmdDef for a char *(*callback) (const char *text,
>> int state). But for real benefit, we need connection object, so we could
>> e.g. list only inactive networks for 'net-start' command. And this is
>> the problem, because we would have to make this object global (since
>> readline functions does not allow passing any opaque value).
> 
> As gross as it is, a global object isn't entirely bad - virsh is
> single-threaded.  And even if we want to make virsh threaded at some
> point, I still think we can get away with adding a thread-local access
> scheme.
> 
>>
>> 2.) expand each command definition with its own completer. So e.g. for
>> start commands we could only list inactive domains, networks, pools,
>> whatever. For destroy only active objects. And so on.
> 
> So maybe we want both - an option-based completer that generates the
> initial list, and a command-based completer that can then prune out
> irrelevant options?
> 

Well, I would say that is the highest goal to be achieved. Although that
implies parsing during options generation.

But I don't think I get it. Option-based completer generates list for
given option, command-based completer generates list for given command
(entries from this list are options). Take detach-interface for
instance. This have some options:
--mac: here we want option-based completer to list mac addresses of a
NICs of a domain specified by
--domain: since this could be left out we want here command-base
completer to either list all domains, or list only those domains which
have a NIC.

So then we get:

# detach-interface <TAB><TAB>
--mac --persistent domain1 domain2

# detach-interface domain1 --mac <TAB><TAB>
00:11:22:33:44:55 01:23:45:67:89

My point is - I can't see any pruning here. But maybe I've chosen wrong
example. However, this example shows we need both types of completer.

Michal