[libvirt] [PATCH v2 0/9] Incremental Backup API additions

[Jiri Denemark]

On Fri, Oct 12, 2018 at 00:10:02 -0500, Eric Blake wrote:
> The following is the latest version of my API proposal for
> incremental backups.
> 
> I have even more work-in-progress patches on top of these:
> https://repo.or.cz/libvirt/ericb.git
> which I am slowly improving to be more in line with my thread
> on the overview of the API usage:
> https://www.redhat.com/archives/libvir-list/2018-October/msg00217.html
> 
> But I am fairly satisfied that the API as presented is sufficient for
> everything I have still been implementing in the qemu driver, and
> that even when qemu is slightly tweaked (such as dropping the x-
> prefix on various commands, or maybe adding a new command to make
> it easier to compute the estimated size of the union of several
> bitmaps), those changes will be limited to the src/qemu directory
> rather than affecting the API.
> 
> Since I will be demonstrating the use of this API at the KVM Forum,
> I would really like a decision on whether we can commit the API
> into libvirt now, even if we have to wait for the qemu implementation

No we can't. We did it once in the past and although I don't remember
the exact details I remember it turned out to be a bad idea. Also
pushing an API with no implementation doesn't really make sense since
the API is unusable until it is implemented in some hypervisor driver.

> of the API until qemu stabilizes its interfaces (also, having the
> libvirt API in place gives qemu an incentive to drop the x- prefix
> sooner rather than later).

The presence of public API in libvirt gives no clue to QEMU engineers
that their API provides everything needed and x- prefix should be
dropped. Only working patches implementing the libvirt APIs for QEMU can
provide such feedback to QEMU developers.

Jirka