[libvirt] libvirt API / balloon last-update

[John Ferlan]

On 10/11/2016 03:15 PM, Marko Myllynen wrote:
> Hi,
> 
> I see that recently the last-update field has been added to the balloon
> statistics, this is how it looks like from Python:
> 
> [(<libvirt.virDomain object at 0x7fb45b7faa50>, {'balloon.rss': 960048L,
> 'balloon.swap_in': 0L, 'balloon.usable': 1676424L, 'balloon.unused':
> 1376188L, 'balloon.major_fault': 816L, 'balloon.swap_out': 0L,
> 'balloon.current': 2097152L, 'balloon.maximum': 2097152L,
> 'balloon.available': 2048364L, 'balloon.minor_fault': 460160L,
> 'balloon.last-update': 1476213030L})]
> 
> As you can see, there's an inconsistency as all the other members use
> underscore (_), not dash (-). This actually matters with the PCP plugin
> since PCP metric names can contain _ but not -.

Looks like it was actually added as an output in 2.1.0

http://libvirt.org/git/?p=libvirt.git;a=commit;h=200a40f94ec9427eb7187d9d5396ad3a3f2925c8

There were continued adjustments:

commit id: f57fbd6c4a5dfc8e725f036791e6333d1ab6f04e
commit id: 438c204763f7d8eed79554075f5633545a4a5df1

Since this is output only and we're not setting it for input, it's
almost too bad we cannot treat this as a spelling error and change it. I
tried looking through history for other cross version instances of
changing output, but didn't find any. Closest I could come was the
blkiotune parameters which can take both _ and - for their names, but
display _ in the name.

> 
> Now that last-update is part of the API in 2.3 I guess it's too late to
> change this but it would nice if in the future the member names could be
> kept consistent and underscore used for new members, as it has been so far.
> 

Hard to be always vigilant... even harder when input parameters prefer
the dash model (see blkdeviotune for example). Sometimes things slip
through the cracks though.

John