Re: [PATCH RFC] docs: Add minimum version depencency policy document

[Christopher Clark <christopher.w.clark@xxxxxxxxx>]

On Thu, Oct 1, 2020 at 7:38 AM Bertrand Marquis
<Bertrand.Marquis@xxxxxxx> wrote:
>
> Hi George,
>
> + Christopher Clark to have his view on what to put for Yocto.
>
> > On 30 Sep 2020, at 13:57, George Dunlap <george.dunlap@xxxxxxxxxx> wrote:
> >
> > Define a specific criteria for how we determine what tools and
> > libraries to be compatible with.  This will clarify issues such as,
> > "Should we continue to support Python 2.4" moving forward.
> >
> > Note that CentOS 7 is set to stop receiving "normal" maintenance
> > updates in "Q4 2020"; assuming that 4.15 is released after that, we
> > only need to support CentOS / RHEL 8.
> >
> > Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> > ---
> >
> > CC: Ian Jackson <ian.jackson@xxxxxxxxxx>
> > CC: Wei Liu <wl@xxxxxxx>
> > CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > CC: Jan Beulich <jbeulich@xxxxxxxx>
> > CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > CC: Julien Grall <julien@xxxxxxx>
> > CC: Rich Persaud <persaur@xxxxxxxxx>
> > CC: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
> > ---
> > docs/index.rst                        |  2 +
> > docs/policies/dependency-versions.rst | 76 +++++++++++++++++++++++++++
> > 2 files changed, 78 insertions(+)
> > create mode 100644 docs/policies/dependency-versions.rst
> >
> > diff --git a/docs/index.rst b/docs/index.rst
> > index b75487a05d..ac175eacc8 100644
> > --- a/docs/index.rst
> > +++ b/docs/index.rst
> > @@ -57,5 +57,7 @@ Miscellanea
> > -----------
> >
> > .. toctree::
> > +   :maxdepth: 1
> >
> > +   policies/dependency-versions
> >    glossary
> > diff --git a/docs/policies/dependency-versions.rst 
> > b/docs/policies/dependency-versions.rst
> > new file mode 100644
> > index 0000000000..d5eeb848d8
> > --- /dev/null
> > +++ b/docs/policies/dependency-versions.rst
> > @@ -0,0 +1,76 @@
> > +.. SPDX-License-Identifier: CC-BY-4.0
> > +
> > +Build and runtime dependencies
> > +==============================
> > +
> > +Xen depends on other programs and libraries to build and to run.
> > +Chosing a minimum version of these tools to support requires a careful
> > +balance: Supporting older versions of these tools or libraries means
> > +that Xen can compile on a wider variety of systems; but means that Xen
> > +cannot take advantage of features available in newer versions.
> > +Conversely, requiring newer versions means that Xen can take advantage
> > +of newer features, but cannot work on as wide a variety of systems.
> > +
> > +Specific dependencies and versions for a given Xen release will be
> > +listed in the toplevel README, and/or specified by the ``configure``
> > +system.  This document lays out the principles by which those versions
> > +should be chosen.
> > +
> > +The general principle is this:
> > +
> > +    Xen should build on currently-supported versions of major distros
> > +    when released.
> > +
> > +"Currently-supported" means whatever that distro's version of "full
> > +support".  For instance, at the time of writing, CentOS 7 and 8 are
> > +listed as being given "Full Updates", but CentOS 6 is listed as
> > +"Maintenance updates"; under this criterium, we would try to ensure
> > +that Xen could build on CentOS 7 and 8, but not on CentOS 6.
> > +
> > +Exceptions for specific distros or tools may be made when appropriate.
> > +
> > +One exception to this is compiler versions for the hypervisor.
> > +Support for new instructions, and in particular support for new safety
> > +features, may require a newer compiler than many distros support.
> > +These will be specified in the README.
> > +
> > +Distros we consider when deciding minimum versions
> > +--------------------------------------------------
> > +
> > +We currently aim to support Xen building and running on the following 
> > distributions:
> > +Debian_,
> > +Ubuntu_,
> > +OpenSUSE_,
> > +Arch Linux,
> > +SLES_,
> > +Yocto_,
> > +CentOS_,
> > +and RHEL_.
> > +
> > +.. _Debian: https://www.debian.org/releases/
> > +.. _Ubuntu: https://wiki.ubuntu.com/Releases
> > +.. _OpenSUSE: https://en.opensuse.org/Lifetime
> > +.. _SLES: https://www.suse.com/lifecycle/
> > +.. _Yocto: https://wiki.yoctoproject.org/wiki/Releases
> > +.. _CentOS: https://wiki.centos.org/About/Product
> > +.. _RHEL: https://access.redhat.com/support/policy/updates/errata
> > +
> > +Specific distro versions supported in this release
> > +--------------------------------------------------
> > +
> > +======== ==================
> > +Distro   Supported releases
> > +======== ==================
> > +Debian   10 (Buster)
> > +Ubuntu   20.10 (Groovy Gorilla), 20.04 (Focal Fossa), 18.04 (Bionic 
> > Beaver), 16.04 (Xenial Xerus)
> > +OpenSUSE Leap 15.2
> > +SLES     SLES 11, 12, 15
> > +Yocto    3.1 (Dunfell)
>
> Yocto only supports one version of Xen (as there is usually only one xen 
> recipe per yocto version)

I'm not sure that's totally accurate: the Yocto Xen recipes are
written to support backwards compatibility with older versions of Xen.
In general, care and effort has been expended to support building with
multiple versions of Xen with the same recipes, via variable override
or bbappend, and it is expected to work.

> which can make the version here a bit tricky:
> Yocto 3.1 (Dunfell) supports only Xen 4.12
> Yocto 3.2 (Gategarth) support only Xen 4.14 but has a Yocto master recipe 
> which should actually be used
> by someone who would want to try Xen master.
>
> So I would suggest to put Yocto 3.2 here only.
>
> @Christopher: what is your view here ?

Thanks for asking. I don't quite agree with that recommendation: I
think Dunfell does belong, with an indication that it requires
Gatesgarth meta-virtualization. Dunfell is the LTS release, so a
compatibility statement about it is important. ie:

Yocto 3.1 (Dunfell + Gatesgarth meta-virtualization)

Effort has already been made within Yocto to make the Gatesgarth
meta-virtualization layer compatible with Dunfell open-embedded core,
specifically to allow newer Xen to be used with the LTS Dunfell
software from the core layers. I would hope that any issues that are
found with that configuration will be posted so they can be fixed.

thanks,

Christopher

>
> Cheers
> Bertrand
>
> > +CentOS   8
> > +RHEL     8
> > +======== ==================
> > +
> > +.. note::
> > +
> > +   We also support Arch Linux, but as it's a rolling distribution, the
> > +   concept of "security supported releases" doesn't really apply.
> > --
> > 2.25.1
> >
> >
>