Re: [Xen-devel] [PATCH 10/18] INSTALL: Mention kconfig

[Doug Goldstein <cardoe@xxxxxxxxxx>]

On Fri, Oct 05, 2018 at 06:29:09PM +0100, Ian Jackson wrote:
> Firstly, add a reference to the documentation for the kconfig system.
> 
> Secondly, warn the user about the XEN_CONFIG_EXPERT problem.
> 
> CC: Doug Goldstein <cardoe@xxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxx>

Reviewed-by: Doug Goldstein <cardoe@xxxxxxxxxx>

> ---
>  INSTALL | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/INSTALL b/INSTALL
> index 9aa9ebdddc..62b0162864 100644
> --- a/INSTALL
> +++ b/INSTALL
> @@ -19,6 +19,26 @@ following compile process. Once configure is done, make(1) 
> has to be
>  called. Also make(1) recognizes certain arguments. The following sections
>  will give an overview.
>  
> +Xen Hypervisor
> +==============
> +
> +Xen itself is configured via a `kconfig' system borrowed from Linux.
> +See docs/misc/kconfig.txt.
> +
> +Note that unlike with Linux, and contrary to that document, you cannot
> +look at Kconfig files, or the default or generated config files etc.,
> +to find available configuration options.  This is because it is only
> +supported (and security supported) by the Xen Project, to change a
> +small subset of the options.  Attempts to change other options will be
> +silently overriden.  The only way to find which configuration options
> +are available is to run `make menuconfig' or the like.
> +
> +You can counter-override this behaviour by setting XEN_CONFIG_EXPERT=y
> +in your environment.  However, doing this is not supported and the
> +resulting configurations do not receive security support.  If you set
> +this varible there is nothing stopping you setting dangerously
> +experimental combinations of features - not even any warnings.

Not really true because the shim is supported and relies on
XEN_CONFIG_EXPERT but certainly better to make users aware than blindly
hiding everything from them. I'd still argue that eventually we'll get
rid of this because most distros build with XEN_CONFIG_EXPERT on and
most Xen devs I know just have it set in their environment.

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