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Re: [libvirt] [PATCH v2 3/3] network: Taint networks that are using hook script



On 02/07/2014 10:52 PM, Antoni Segura Puimedon wrote:
>
> ----- Original Message -----
>> From: "Laine Stump" <laine laine org>
>> To: libvir-list redhat com
>> Cc: "Michal Privoznik" <mprivozn redhat com>
>> Sent: Friday, February 7, 2014 1:17:10 PM
>> Subject: Re: [libvirt] [PATCH v2 3/3] network: Taint networks that are using hook script
>>
>> On 02/05/2014 12:11 PM, Michal Privoznik wrote:
>>> Basically, the idea is copied from domain code, where tainting
>>> exists for a while. Currently, only one taint reason exists -
>>> VIR_NETWORK_TAINT_HOOK to mark those networks which caused invoking
>>> of hook script.
>> What's missing here is that the network status XML doesn't include a
>> <taint> element.
>>
>> Also, I think if a network is tainted, and domain that connects to that
>> network should be tainted as well.
>>
>> Of course what would make this more useful would be if would could
>> determine when a hook script actually *did* something for a particular
>> network/interface (since presumably people are usually going to write
>> their network hook scripts to only take action for particular networks
>> and/or domains, not for *all* networks). I don't know that there's a way
>> to do that without either 1) having a different hook script for each
>> network, or 2) trusting the hook script to return some sort of status
>> indicating whether or not it did anything. Obviously (2) is not a good
>> idea, but we may want to think about (1) in the future (for qemu and lxc
>> hook scripts as well) - instead of just looking for
>> /etc/libvirt/hook/network, we could first look for
>> /etc/libvirt/hook/network.${netname} and exec that instead if found (or
>> in addition). But I think that can be deferred until later.
> Actually I kind of like the option (2). I think it could make a lot of sense
> that the hook would be able to add an attribute to the network definition
> xml, e.g. <bandwidth hooked="1"> so that libvirt would know that that part
> has been taken care of by the hook. Of course, it might be a bad idea for
> libvirt to blindly accept any kind of modification, but something like what
> I propose does not seem eminently dangerous.

The reason I don't like option (2) is that it requires trusting the hook
to leave its mark if it modifies anything, and that's exactly why we
want to taint the networks that call a hook - because we don't/can't
trust the hook.

I wonder if there might be some way to allow a hook to add information
to the network's xml in some well-defined location, though. This
information would not be used/trusted by libvirt at all, but would only
be there, for example, so that a later "stop/unplug" hook could retrieve
it, rather than being required to keep its state externally.


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