Libguestfs - Mar 2020 - [RHEL] nbdkit & libnbd for RHEL AV 8.3.0

Some thoughts on nbdkit and libnbd in RHEL Advanced Virtualization 8.3.0.

We have two bugs open for rebases:

* https://bugzilla.redhat.com/show_bug.cgi?id=1809231
  "Rebase nbdkit to at least 1.18+ in RHEL AV 8.3.0"
* https://bugzilla.redhat.com/show_bug.cgi?id=1809674
  "Rebase libnbd for RHEL-AV 8.3.0"

The rules for rebasing are (well, these are _my_ rules):

(1) Must not introduce API/ABI incompatibility or regressions.
(2) Must introduce worthwhile new features relevant to RHEL customers.
(3) Must maintain any backported features from earlier RHEL.

For nbdkit it makes sense to rebase to 1.18 since there are
significant features relevant to virt-v2v (see my summary in
https://bugzilla.redhat.com/show_bug.cgi?id=1809231#c1).  So for
nbdkit I have added a rhel-8.3 branch upstream, currently based on
nbdkit 1.18.2.  Since upstream 1.18.2 contains everything that was
backported to RHEL AV 8.2 there is no need for any backports at this
time.

I should note that RHEL has never shipped the ext2 plugin, so the fact
it was deprecated upstream (replaced with Eric's new ext2 filter) is
irrelevant to RHEL.

For libnbd, there are not really any significant features upstream,
but the Golang bindings (not upstream yet) have been requested for
RHEL (https://bugzilla.redhat.com/1814538).  I think we can easily do
this without rebasing, but with a cherry pick of these bindings.

If there's anything I've missed, let me know.  This situation could
evolve as we get further requests.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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