[libvirt] uses of /etc/libvirt/<driver>/

[Jim Fehlig]

Michal Privoznik wrote:
> On 18.03.2014 02:20, Eric Blake wrote:
>> On 03/17/2014 05:46 PM, Jim Fehlig wrote:
>>> I received a report about an odd use case of /etc/libvirt/<driver>/
>>> config files, and would like to hear some opinions about it.  The user
>>> "preps" a host by mounting a remote fs containing VM images and config,
>>> creates links in /etc/libvirt/<driver>/dom.xml to
>>> /mnt-point/whatever/dom.xml, and starts libvirtd.  All is well until
>>> there is a need to modify the VM config (e.g. virsh setmaxmem ...
>>> --config), at which point libvirt replaces the link with a file
>>> containing the new config, instead of updating the contents of the
>>> linked file.
>>
>> Not a valid use case.  Instead, the user should 'virsh define' (or
>> otherwise use the libvirt APIs).
>>
>>>
>>> I suppose I've always considered the contents of /etc/libvirt/<driver>/
>>> private to libvirt, with a "modify at your own risk" warning, ignoring
>>> that it is user configuration in /etc.  What are the guidelines for
>>> modifying the contents of these directories?  Would the above be
>>> considered valid use?
>>
>> Point your user to:
>> http://wiki.libvirt.org/page/FAQ#Where_are_VM_config_files_stored.3F_How_do_I_edit_a_VM.27s_XML_config.3F
>>
>>
>> and hopefully they will quit abusing files under /etc, as that usage is
>> explicitly unsupported.  We only support modifications made through
>> libvirt APIs.
>
> But they are modifying XML through libvirt APIs (virsh setmaxmem ...).
> However, if they are sharing XML over several hosts, it won't work
> (this really is unsupported). You don't want libvirtd to be polling
> for XML definition file changes made from outside and then re-parsing
> the file.

Yes, I would *not* want that behavior :).

>
> What they could do, is to symlink the <driver> directory instead of
> individual XML files there.

Or mount the <driver> directory with their config, or virDomainDefineXML
as Eric suggests.  I guess the question was more about what users are
allowed to do with files in this directory.  I've always claimed "not
much".  Thanks to all for confirming that.

Regards,
Jim