Runtime adjustment of hypervisor parameters

[Juergen Gross <jgross@suse.com>]

Last year Jan posted a patch series to change hypervisor log level
thresholds via xl command [1]. This approach was later modified by Wei
resulting in patch series [2].

I'd like to follow up with another approach being able to do the same,
but being much more flexible:

Instead of controlling only loglvl I suggest to add a xl command

xl xen-param <parameters>

which will take a <parameters> string being parsed by the hypervisor
the same way it is parsing boot parameters. Allowed parameters are
specified in the hypervisor the same way as boot parameters, but with
another set of macros (e.g. custom_runtime_param(), ...). Often enough
(e.g. in the loglvl case) the definitions could be just the same, while
in other cases they might differ a little bit (example: conring_size
would require a different handling as at boot time due to race
condition handling).

Parsing functions could be reused in most cases, they'd just need to
lose the __init modifier.

What do you think: is this approach sensible, or can I just put it into
/dev/null instead of starting with the patches?


Juergen

[1]
https://lists.xenproject.org/archives/html/xen-devel/2016-03/msg00694.html
[2]
https://lists.xenproject.org/archives/html/xen-devel/2016-07/msg00228.html

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