matching Qemu version to Xen version, how critical?

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matching Qemu version to Xen version, how critical?

Mark Pryor
Hello,


there have been several posts lately, like the above, but not as complete as it, but they all go like this:
I install xen-4.x (usually 4.8) on Stretch and try to launch a Windows install VM. It either never starts or I
run out of memory before I'm done.

But in the above, Mr. Jaser goes further and tries a source build of xen-4.9 (in Stretch) and there is no such trouble.

All the recent Xen packages for Ubuntu and Debian do not match Qemu version with Xen as found in upstream.
In other words:

Ubuntu Artful: qemu->2.10, xen->4.9. upstream has qemu->2.8

Debian Stretch: qemu->2.8, xen->4.8. Should be qemu->2.7

Ubuntu Zesty: same as Stretch

Ubuntu Xenial: qemu->2.5, xen->4.6. Should be qemu->2.2

Artful has the largest deviation between distro and upstream for qemu version.
Certainly, the distro builds are good in the sense that both Xen and Qemu share the same basic libraries
during build. So as long as they build and install, things should be OK?

When we do a source build none of this issue comes up, since Qemu sources are carried via git and tarball.

I've recently done a port of the Artful xen-4.9 to Stretch and I finished the Xen build in Stretch before I realized that
qemu in Artful depends on the libxen-4.9 headers and libraries.

So I went further and did a build of qemu-2.8 for Stretch with matching xen-4.9 libraries.

I already have done this with success for xen-4.8, by building qemu-2.7 with xen-4.8 libraries. This combo installs and tests well, launching and running a Win7 VM. I've yet to test my Xen-4.9 combo for Stretch.

Please tell me it doesn't matter what version of qemu is used with Xen, as long as they are build together. How critical can it be?

PryMar56
##xen-packaging on freenode IRC



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Re: matching Qemu version to Xen version, how critical?

Ian Jackson-2
Mark Pryor writes ("matching Qemu version to Xen version, how critical?"):
...
> Please tell me it doesn't matter what version of qemu is used with
> Xen, as long as they are build together. How critical can it be?

It's not very critical, if you are using a released version of Xen.
In particular, if it builds, you're unlikely to go very far wrong.

NB though that (as you suggest from "built together") the Xen control
libraries that qemu uses 1. do not have a stable ABI until recently
(sorry) 2. do not have a stable interface to the hypervisor.

So unless you are using the very latest bits, you must rebuild when
you use a different Xen version.

Additionally, the qemu configure script works by determining the Xen
version (rather than by looking for individual features) and keying
everything off that.  So if you are using xen-unstable, you will find
that some qemu versions don't build.

Ian.

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Re: matching Qemu version to Xen version, how critical?

Mark Pryor
In reply to this post by Mark Pryor
Hello,



on Oct 02, Debian-security released 8 fixes for qemu-2.8. In total there are
46 patches since the release of qemu-2.8 on Jul 21.

As shown, in the fpaste, I applied these 46 to the upstream xen-4.9 tarball while
trying to package in Stretch. All applied cleanly.

As a source of qemu fixes xen-4.9, I've looked here:

you can see there is only 1 fix since the release of xen-4.9.0 (Jun 27).

Any harm in using the debian-delta for qemu fixes? Should these be auto-tested by xenproject?

PryMar56

On Thursday, October 5, 2017 3:51 AM, Ian Jackson <[hidden email]> wrote:


Mark Pryor writes ("matching Qemu version to Xen version, how critical?"):

...
> Please tell me it doesn't matter what version of qemu is used with
> Xen, as long as they are build together. How critical can it be?


It's not very critical, if you are using a released version of Xen.
In particular, if it builds, you're unlikely to go very far wrong.

NB though that (as you suggest from "built together") the Xen control
libraries that qemu uses 1. do not have a stable ABI until recently
(sorry) 2. do not have a stable interface to the hypervisor.

So unless you are using the very latest bits, you must rebuild when
you use a different Xen version.

Additionally, the qemu configure script works by determining the Xen
version (rather than by looking for individual features) and keying
everything off that.  So if you are using xen-unstable, you will find
that some qemu versions don't build.

Ian.

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Re: matching Qemu version to Xen version, how critical?

Ian Jackson-2
Anthony, and Stefano, see below.  I haven't investigated at all.

Mark: I think you are probably fine to use the Debian version.

Mark Pryor writes ("Re: [Xen-users] matching Qemu version to Xen version, how critical?"):

> Hello,
>
> https://paste.fedoraproject.org/paste/o15OrLa~PY98S3EPm6P-Ag/
>
> https://tracker.debian.org/news/877656
>
>  
> on Oct 02, Debian-security released 8 fixes for qemu-2.8. In total there are
> 46 patches since the release of qemu-2.8 on Jul 21.
>
> As shown, in the fpaste, I applied these 46 to the upstream xen-4.9 tarball
> while
> trying to package in Stretch. All applied cleanly.
>
> As a source of qemu fixes xen-4.9, I've looked here:
> http://xenbits.xen.org/gitweb/?p=qemu-xen.git;a=shortlog;h=refs/heads/
> staging-4.9
>
> you can see there is only 1 fix since the release of xen-4.9.0 (Jun 27).
>
> Any harm in using the debian-delta for qemu fixes? Should these be auto-tested
> by xenproject?
>
> PryMar56
>
> On Thursday, October 5, 2017 3:51 AM, Ian Jackson <[hidden email]>
> wrote:
>
>
> Mark Pryor writes ("matching Qemu version to Xen version, how critical?"):
>
> ...
> > Please tell me it doesn't matter what version of qemu is used with
> > Xen, as long as they are build together. How critical can it be?
>
>
> It's not very critical, if you are using a released version of Xen.
> In particular, if it builds, you're unlikely to go very far wrong.
>
> NB though that (as you suggest from "built together") the Xen control
> libraries that qemu uses 1. do not have a stable ABI until recently
> (sorry) 2. do not have a stable interface to the hypervisor.
>
> So unless you are using the very latest bits, you must rebuild when
> you use a different Xen version.
>
> Additionally, the qemu configure script works by determining the Xen
> version (rather than by looking for individual features) and keying
> everything off that.  So if you are using xen-unstable, you will find
> that some qemu versions don't build.
>
> Ian.
>
> _______________________________________________
> Xen-users mailing list
> [hidden email]
> https://lists.xen.org/xen-users
>
>

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Re: matching Qemu version to Xen version, how critical?

Stefano Stabellini-4
On Tue, 10 Oct 2017, Ian Jackson wrote:
> Anthony, and Stefano, see below.  I haven't investigated at all.
>
> Mark: I think you are probably fine to use the Debian version.

Yes, Ian is right.

In the past upstream QEMU didn't do a very good job at applying fixes to
stable trees, so I haven't been looking closely for changes there. In
fact, it often happened that the qemu-xen stable trees would have more
fixes than the corresponding QEMU stable trees.

It is very good to see that this has changed. Many fixes were applied to
qemu/stable-2.8, that today are not in qemu-xen/stable-4.9. But we can
start backporting now. Anthony, would you be up for watching the QEMU
stable trees more closely and backporting fixes from there to the
qemu-xen stable trees going forward?


> Mark Pryor writes ("Re: [Xen-users] matching Qemu version to Xen version, how critical?"):
> > Hello,
> >
> > https://paste.fedoraproject.org/paste/o15OrLa~PY98S3EPm6P-Ag/
> >
> > https://tracker.debian.org/news/877656
> >
> >  
> > on Oct 02, Debian-security released 8 fixes for qemu-2.8. In total there are
> > 46 patches since the release of qemu-2.8 on Jul 21.
> >
> > As shown, in the fpaste, I applied these 46 to the upstream xen-4.9 tarball
> > while
> > trying to package in Stretch. All applied cleanly.
> >
> > As a source of qemu fixes xen-4.9, I've looked here:
> > http://xenbits.xen.org/gitweb/?p=qemu-xen.git;a=shortlog;h=refs/heads/
> > staging-4.9
> >
> > you can see there is only 1 fix since the release of xen-4.9.0 (Jun 27).
> >
> > Any harm in using the debian-delta for qemu fixes? Should these be auto-tested
> > by xenproject?
> >
> > PryMar56
> >
> > On Thursday, October 5, 2017 3:51 AM, Ian Jackson <[hidden email]>
> > wrote:
> >
> >
> > Mark Pryor writes ("matching Qemu version to Xen version, how critical?"):
> >
> > ...
> > > Please tell me it doesn't matter what version of qemu is used with
> > > Xen, as long as they are build together. How critical can it be?
> >
> >
> > It's not very critical, if you are using a released version of Xen.
> > In particular, if it builds, you're unlikely to go very far wrong.
> >
> > NB though that (as you suggest from "built together") the Xen control
> > libraries that qemu uses 1. do not have a stable ABI until recently
> > (sorry) 2. do not have a stable interface to the hypervisor.
> >
> > So unless you are using the very latest bits, you must rebuild when
> > you use a different Xen version.
> >
> > Additionally, the qemu configure script works by determining the Xen
> > version (rather than by looking for individual features) and keying
> > everything off that.  So if you are using xen-unstable, you will find
> > that some qemu versions don't build.
 

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Re: matching Qemu version to Xen version, how critical?

Anthony PERARD-2
On Tue, Oct 10, 2017 at 04:47:37PM -0700, Stefano Stabellini wrote:

> On Tue, 10 Oct 2017, Ian Jackson wrote:
> > Anthony, and Stefano, see below.  I haven't investigated at all.
> >
> > Mark: I think you are probably fine to use the Debian version.
>
> Yes, Ian is right.
>
> In the past upstream QEMU didn't do a very good job at applying fixes to
> stable trees, so I haven't been looking closely for changes there. In
> fact, it often happened that the qemu-xen stable trees would have more
> fixes than the corresponding QEMU stable trees.
>
> It is very good to see that this has changed. Many fixes were applied to
> qemu/stable-2.8, that today are not in qemu-xen/stable-4.9. But we can
> start backporting now. Anthony, would you be up for watching the QEMU
> stable trees more closely and backporting fixes from there to the
> qemu-xen stable trees going forward?

From my observation, there is one stable release for every new QEMU
release, but there is no stable tree (at least not the way stable tree
are maintained for xen).

For e.g., for QEMU 2.10, release in August, there is one stable release
2.10.1 released 1 month later, and I don't expect any other stable
release. The stable-2.10 branch was not updated/created between both
release.


As for watching those releases, yes, I can do that, as soon as I figure
out when I can update the qemu-xen tree of a released Xen version. I
never asked.

Regards,

--
Anthony PERARD

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