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Re: [PATCH] xen/argo: Command line handling improvements
- To: Christopher Clark <christopher.w.clark@xxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 21 May 2025 21:43:31 +0100
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "Daniel P . Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>, Denis Mukhin <dmkhn@xxxxxxxxx>
- Delivery-date: Wed, 21 May 2025 20:43:39 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21/05/2025 2:01 am, Christopher Clark wrote:
> On Tue, May 20, 2025 at 3:10 PM Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx> wrote:
>
> Treat "argo" on the command line as a positive boolean, rather
> than requiring
> the user to pass "argo=1/on/enable/true".
>
> Move both opt_argo* variables into __ro_after_init. They're set
> during
> command line parsing and never modified thereafter.
>
>
> Instead of binding to static values set at boot, would
> boolean_runtime_param be acceptable?
No, for several reasons.
Sure, you could dynamically turn it on, but existing domains can't use
it because argo_init() wasn't called on them. Now consider what happens
when dynamically turning it off behind the back of a domain which was
using it.
All the existing runtime controls are for properties that are not
visible to guests. Adding opt_argo to this list would create a lot of
carnage.
(Like almost everything else in Xen), Argo is entirely broken with
respect to enumeration and controls. And while this isn't your fault
for having copied the status quo, it is still a problem needing fixing.
Argo's availability needs advertising to the toolstack like all other
features, and the toolstack needs to be able to choose the Argo settings
on a per-VM basis. Like everything else about VMs, the Argo-ness must
be invariant for the lifetime of the domain.
This means changes to sysctls/domctls, which IMO are prerequisites for
Argo to move from Tech Preview to Supported. In a world where such
controls existed, the argo cmdline option would really only be for
someone trying to disable Argo globally.
This particular patch comes simply from me trying to experiment with
Argo to sort out the XTF test, and deciding that the behaviour was
objectionable enough that I'd improve it.
~Andrew
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