On Thu, Jan 21, 2016 at 12:01 PM, Peter <peter@xxxxxxxxxxxxxxxx> wrote:
> On 15/01/16 05:57, George Dunlap wrote:
>> As mentioned yesterday, Xen 4.6 packages are now available for
>> testing. These also include an update to libvirt 1.3.0, in line with
>> what's available for CentOS 7. Please test, particularly the upgrade
>> if you can, and report any problems here.
>
> Per conversation in IRC, Xen 4.6 no longer includes xend and therefore
> no longer has the "xm" command. This is problematic for people who may
> be using xm in various scripts on their host (such as home-brewed backup
> scripts).
>
> I think it's a bad idea to break this functionality without warning by
> allowing a simple "yum update" to remove it. You will take a lot of
> people by surprise and cause such scripts to stop working, if people are
> running yum cron the situation becomes even worse.
Thanks, PJ, for your input.
Just to be clear:
1. In the Xen 4.4 packages (first released October 2014), xend was
disabled by default; so anyone using xend at the moment has already
manually intervened to enable deprecated functionality
2. In 4.4, the first time xm was executed, it printed this warning:
---
xend is deprecated and scheduled for removal. Please migrate to another
toolstack ASAP.
See http://wiki.xen.org/wiki/Choice_of_Toolstacks for information on
other alternatives, including xl which is designed to be a drop in
replacement for xm (http://wiki.xen.org/wiki/XL).
---
3. ...and on every subsequent invocation, it printed this warning:
"WARNING: xend/xm is deprecated"
I think this constitutes "warning" that the functionality was going to
break at some point. :-)
Also, in most cases "s/xm/xl/g;" Just Works; most people have reported
that changing from xm -> xl was pretty painless. So this isn't like
upgrading from Python 2 to Python 3 (or QT 4 to 5, or...).
> I think that due to this lack of backwards compatibility with Xen 4.4
> and earlier versions it would be a good idea to not force the upgrade on
> people who are not wary of it. I propose that the new packages carry
> the name "xen46" and they purposefully conflict with the old "xen"
> packages. That will require people to take positive action to do the
> upgrade and hence avoid breaking systems unintentionally.
This would avoid breaking things for people still using xm, which
certainly has some value. However it has some costs:
* The packages between C6 and C7 will now be slightly different,
increasing the maintenance burden. This is not only in the spec file,
but also in all the associated scripting machinery for managing
packages in the CBS and smoke-testing packages before pushing them
publicly.
* Instructions for installing Xen are now differend between C6 and C7,
and slightly more complicated, as they have to explain about Xen 4.6
vs alternatives.
* Users who have heeded the warning and switched to xl will have to
make an extra effort to switch to Xen 4.6. If they don't follow
centos-virt, they may not notice that there's a new package to upgrade
to.
I'm a developer, not a server admin, so I can't gauge how important
this issue is. Before making such a change, I'd like to hear opinions
from other people in the community about how important (or not) it is
to avoid breaking xm, given the ample warning (>1 year) users have
had.
On the other hand, explicitly moving to a "xen${VER}" (both for C6 and
C7) would make it simpler for people to step up and maintain older
versions in parallel if anybody wanted to do so.
Thanks again, Peter, for bringing this up.
Peace,
-George
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