[libvirt] [PATCH 0/2] qemu: Enable -blockdev support (blockdev-add saga)

[Peter Krempa]

On Fri, Sep 13, 2019 at 23:35:47 +0200, Martin Kletzander wrote:
> On Fri, Sep 13, 2019 at 02:43:53PM +0200, Peter Krempa wrote:
> > To my knowledge, everything in libvirt is now prepared to fully use
> > -blockdev way to configure disks in qemu.
> > 
> > There is one known qemu bug though: Internal snapshots don't work with
> > -blockdev:
> > 
> > https://bugzilla.redhat.com/show_bug.cgi?id=1658981
> > 
> > Since I can't in good faith ask for merging this patchset yet I'd like
> > to give it some more testing I'm suggesting that we push it and revert
> > it during freeze or add a capability check once qemu is fixed.
> > 
> 
> I am very much in favour of getting some testing before releasing such big
> changes.  Any way of not including this in release tarballs is fine, but we
> should also not completely give up on non-blockdev approach until we do actually
> release it, if only because by having this in for the whole development period
> only to disable it for release would mean that we are releasing something we did
> not test at all for a whole cycle.

At this point it would be more like half of a cycle. Also once we enable
it anyways (even for some future-qemu-only) the testing given will
decrease by time into the almost-bitrot region.

To facilitate some deliberate testing I've added the possibility to
control the qemu capability bits from the qemu namespace:

https://libvirt.org/drvqemu.html#xmlnsfeatures

That allows developers and uses who wish to experiment to deliberately
disable any feature. (Obviously resulting breakage may be considered
unsupported)
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