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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Sep 30, 2020 at 01:57:36PM +0100, George Dunlap 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_.

Could we add FreeBSD here, I've been packaging Xen there for quite
some time now, and try to keep it working.

It's an interesting target because it has quite a different toolchain
as it's fully llvm based (clang + lld) and then it's using the ELF
Toolchain.

https://www.freebsd.org/releases/

Not sure if we want to rename the current section to Linux distros and
add a different one for other OSes.

Thanks, Roger.