[libvirt-users] Possible to edit/apply nwfilter at runtime?

[Laine Stump]

On 03/30/2018 04:29 PM, Andre Goree wrote:
> On 2018/02/16 12:12 pm, Daniel P. Berrangé wrote:
>> On Fri, Feb 16, 2018 at 11:59:42AM -0500, Andre Goree wrote:
>>> I'm trying to determine if it's possible to edit/attach/apply
>>> nwfilter rules
>>> at runtime?  I.e., after a VM is already running, can I apply a
>>> nwfilter to
>>> the VM and have it work without rebooting the machine?  Thus far,
>>> I've not
>>> come across a way to do so, but I thought I'd ask here before I chase my
>>> tail around Google.
>>
>> Simply re-define the nwfilter in question using  virsh nwfilter-define.
>> Any VMs using that filter will automatically update.
>>
>>
>> Regards,
>> Daniel
>> -- 
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>> |: https://libvirt.org         -o-           
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> 
> 
> I've run into an issue here that I thought you might have some insight on.
> 
> I can't seem to "re-define" a nwfilter. 

Why is that? The only thing (aside from a syntax error) that would cause
nwfilter-define to fail when the filter already exists would be if you
tried to define the filter with the same name but different (or
non-existent) uuid, or vice versa. As long as the new definition has the
same name and uuid, there should be no problem.

If you're relying on libvirt to provide the uuid when the filter is
originally defined, just modify your "update" script to do virsh
nwfilter-dumpxml to read the current text of the filter, modify that
text, then send the result to virsh nwfilter-define (that's exactly what
virsh nwfilter-edit does).

> I must first 'virsh
> nwfilter-undefine' then 'virsh nwfilter-define', or else use 'virsh
> nwfilter-edit'.  The problem being, I cannot use nwfilter-edit from a
> script :/
> 
> My real problem is that if I want to add to and/or adjust a filter for a
> VM, I basically have to call 'virsh update-device ...' which
> unfortunately leaves the VM wide-open for a short period of time, which
> is very undesirable.
> 
> I wonder if there's a way to edit the nwfilter _without_ libvirt having
> to drop the filter for the VM before applying any changes.
> 

If this really doesn't work when using the same name and uuid as the
original nwfilter, please reply with the exact error message you
receive, along with the output of virsh nwfilter-dumpxml prior to the
attempt at redefinition, and the text you are sending that results in a
failed nwfilter-define.