Re: [ovirt-devel] [VDSM] about improved libvirt-python bindings
On Wed, Feb 18, 2015 at 07:53:17AM -0500, Francesco Romani wrote:
Hi,
during my sampling overhaul effort I faced various times a mismatch between
what the libvirt-python API offers for bulk stats and what VDSM needs.
The return value of bulk stats is a something like
[(dom1, {dict_of_bulk_stats1}), {dom2, {dict_of_bulk_stats2}), ...]
While VDSM almost all the times really wants to use
{ dom_uuid_1: dict_of_bulk_stats_1, dom_uuid_2: dict_of_bulk_stats_2 }
translation is trivial to be coded, but bulk stats retrieval is quite
always in the hot path. Moreover, this is just wasteful.
How big is the waste?
But in general, there will always be a not-perfect match from libvirt-python
and VDSM needs. This is expected: libvirt-python needs to be more generic.
So, I coded a Proof of Concept extension module which *complements*
and not *replaces* the libvirt-python API.
Does it require Vdsm to hold two open connections to libvirtd? I'm a bit
worried about possible races and inconsistencies that can pop up due to
this. I'm not expecting huge troubles, just the possiblity that a future
vdsm developer would assume that dom1 and dom1prime are the same since
they represent the same VM, while in case, they come via a different
virconnection and has different attributes.
https://github.com/mojaves/libvirt-python-ovirt
It monkeys-patch some APIs and replace them with VDSM-crafted ones.
If we have enough of monkey patching, it is even easier to just add new APIs
instead of replacing them.
It was a nice and fun hack, but now, the question is: is that a concept worth
developing further? Do we want to use and depend on this module?
I believe that with such a buffer we can gain some agility with respect
to libvirt plans and needs, and the maintainership cost _seems_ fairly low.
Thoughts welcome.
To me, adding this module seems quite expensive: new ovirt project,
inclusion in fedora/el/debian, versioning and release-engineering
hassle. To support the idea, I'd prefer to see a measureable improvement
in architecture or performence, that still alludes me.