Re: [PATCH RESEND 2/2] xen: Allow EXPERT mode to be selected from the menuconfig directly

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 04/05/2020 10:37, Jan Beulich wrote:
> On 04.05.2020 11:30, Julien Grall wrote:
> > Hi Jan,
> >
> > On 04/05/2020 10:18, Jan Beulich wrote:
> > > On 30.04.2020 17:35, Julien Grall wrote:
> > > > On 30/04/2020 15:50, Jan Beulich wrote:
> > > > > On 30.04.2020 16:25, Julien Grall wrote:
> > > > > > EXPERT mode is currently used to gate any options that are in technical
> > > > > > preview or not security supported At the moment, the only way to select
> > > > > > it is to use XEN_CONFIG_EXPERT=y on the make command line.
> > > > > >
> > > > > > However, if the user forget to add the option of one of the make
> > > > > > command (even a clean), then .config will get rewritten. This may lead
> > > > > > to a rather frustrating experience as it is difficult to diagnostic the
> > > > > > issue.
> > > > > Is / will this still be true after Anthony's rework of the build
> > > > > system? Right now we already have
> > > > >
> > > > > clean-targets := %clean
> > > > > no-dot-config-targets := $(clean-targets) \
> > > > >                             ...
> > > > I haven't tried Anthony's rework yet. But I guess the problem would
> > > > be the same if you forget to add XEN_CONFIG_EXPERT=y on make.
> > > Why? xen/.config would get re-written only if kconfig got run in
> > > the first place. It is my understanding that no-dot-config-targets
> > > exist to avoid including .config, and as a result make won't find
> > > a need anymore to cause it to re-made if out of date.
> > kconfig may be executed because you change one of the */Kconfig file.
> > So if you happen to forget XEN_CONFIG_EXPERT=y on your build command
> > line, then you will have your .config rewritten without expert options.
> That's still a build system issue then (if this is really what happens):
> Dependencies of xen/.config shouldn't be evaluated as long as it doesn't
> get used.
I am not sure to understand what you mean by "doesn't get used here". 
When you build Xen, xen/.config is a dependency for the auto-generated 
header. So 'make' will actually check whether there are any modification 
in */Kconfig.
A user would also expect that any modification in a */Kconfig will be 
picked by 'make' when building the hypervisor. This is how it works in 
Linux and I see no reason to diverge in Xen for this.
Cheers,

--
Julien Grall