[libvirt] [PATCH] Allow address lease query with inactive domain

[Amador Pahim]

On Thu, Sep 8, 2016 at 2:46 AM, Laine Stump <laine at laine.org> wrote:
> On 09/07/2016 05:57 AM, Amador Pahim wrote:
>>
>> On Wed, Sep 7, 2016 at 11:41 AM, Daniel P. Berrange <berrange at redhat.com>
>> wrote:
>>>
>>> On Wed, Sep 07, 2016 at 11:18:58AM +0200, Amador Pahim wrote:
>>>>
>>>> The <drive>DomainInterfaceAddresses, when using the source type
>>>> LEASE, does not need the domain to be running. It only checks the
>>>> dhcp lease file and gets the address information from a valid lease,
>>>> if any.
>>>>
>>>> This patch removes the virDomainObjIsActive(vm) check from the LEASE
>>>> query type on both qemu and lxc drivers, keeping it only for query
>>>> type AGENT on qemu driver (since lxc does not support AGENT type).
>>>
>>> I don't think we should do this. IMHO it only makes sense to ask for
>>> the IP address when the guest is actually running. The fact that we
>>> might still happen to have an old IP address stored in the lease
>>> file is merely a happy accident and not something we should guarantee
>>> by exposing ability to get it in the API.
>>
>> The fact that the guest is running does not mean the lease information is
>> accurate. Guest IP can be manually changed. IP can be allocated by
>> someone else between the true virDomainObjIsActive(vm) and the actual
>> DHCPACK. We don't guarantee the information in any case, unless you
>> change the query type to AGENT. One can parse the lease file by itself
>> (and check if the lease is not expired), it's cheaper than create(), query
>> the lease addresses, destroy(). This patch tries to avoid both.
>
>
> (A short explanation of your use case might help us to understand why you
> would want to learn the former IP address of a non-running guest.)
>
> When the guest is running, of course the information in the lease file might
> be incorrect, but that would most likely be caused by a malicious or
> malfunctioning guest. In general though, the lease information probably is
> correct, and the IP address you get back could be used to contact the guest
> (from the host, at least, and assuming necessary ports were open in guest
> and host firewalls, and that the guest was listening on the appropriate
> port).
>
> If the guest *isn't* running though, then by definition the lease
> information is incorrect - you definitely aren't going to be able to reach
> the guest via that address, so it's a bit misleading for libvirt to suggest
> it.

Ok, thank you both for the feedback.