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


On 11/05/2020 14:40, Jan Beulich wrote:
On 11.05.2020 15:30, Julien Grall wrote:
Hi Ian,

Thank you for the clarification.

On 07/05/2020 18:01, Ian Jackson wrote:
Julien Grall writes ("Re: [PATCH RESEND 2/2] xen: Allow EXPERT mode to be selected 
from the menuconfig directly"):
On 04/05/2020 13:34, Ian Jackson wrote:
George Dunlap writes ("Re: [PATCH RESEND 2/2] xen: Allow EXPERT mode to be selected 
from the menuconfig directly"):
On Apr 30, 2020, at 3:50 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
Well, if I'm not mis-remembering it was on purpose to make it more
difficult for people to declare themselves "experts". FAOD I'm not
meaning to imply I don't see and accept the frustration aspect you
mention further up. The two need to be carefully weighed against
one another.

Yes, it was on purpose.  However, I had my doubts at the time and
I think experience has shown that this was a mistake.

I don’t think we need to make it difficult for people to declare
themselves experts, particularly as “all” it means at the moment is,
“Can build something which is not security supported”.  People who
are building their own hypervisors are already pretty well advanced;
I think we can let them shoot themselves in the foot if they want


Can I consider this as an Acked-by? :)

I am happy with the principle of the change.  I haven't reviewed the
details of the commit message etc.

I reviewed the thread and there were two concernes raised:

   * The question of principle.  I disagree with this concern
     because I approve of principle of the patch.

   * Some detail about the precise justificaton as written in
     the commit message, regarding `clean' targets.  Apparently the
     assertion may not be completely true.  I haven't seen a proposed
     alternative wording.

I have checked the latest staging, the `clean` target doesn't trash
.config anymore.

I don't feel I should ack a controversial patch with an unresolved
wording issue.  Can you tell me what your proposed wording is ?
To avoid blocking this change I would be happy to review your wording
and see if it meets my reading of the stated objection.

Here a suggested rewording:

"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 when (re)building or when
using menuconfig, then .config will get rewritten. This may lead to a
rather frustrating experience as it is difficult to diagnostic the

To me this looks very similar to e.g. not suitably overriding the
default toolchain binaries, if one has a need to build with newer
ones than what a distro provides. According to some of my routinely
built configs both can be done by putting suitable entries into
./.config (not xen/.config), removing the need to remember adding
either to the make command line.

I have never heard of ./.config before. So what are you referring to?

But yes, there are ways to make it permanent. But that involves hacking Xen source. This is not a very great approach because if you need to bisect, then you have to remember to apply the change everytime. It also doesn't work if you have to build for multiple different target from the same source.

The compiler is another option that would be worth to move in the Kconfig. I have stopped counting the number of time I mixed up between Arm64, Arm32 and x86 compilers when building Xen...


Julien Grall



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