Re: [Xen-devel] [PATCH 00/12] add per-domain and per-cpupool generic parameters

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.09.18 at 13:02, <jgross@xxxxxxxx> wrote:
> On 18/09/18 12:32, Jan Beulich wrote:
>>>>> On 18.09.18 at 08:02, <jgross@xxxxxxxx> wrote:
>>> Instead of using binary hypervisor interfaces for new parameters of
>>> domains or cpupools this patch series adds support for generic text
>>> based parameter parsing.
>>>
>>> Parameters are defined via new macros similar to those of boot
>>> parameters. Parsing of parameter strings is done via the already
>>> existing boot parameter parsing function which is extended a little
>>> bit.
>>>
>>> Parameter settings can either be specified in configuration files of
>>> domains or cpupools, or they can be set via new xl sub-commands.
>> 
>> Without having looked at any of the patches yet (not even their
>> descriptions) I'm still wondering what the benefit of textual parameters
>> really is: Just like "binary" ones, they become part of the public
>> interface, and hence subsequently can't be changed any more or
>> less than the ones we currently have (in particular, anything valid in
>> a guest config file will imo need to remain to be valid and meaningful
>> down the road).
>> 
>> If this is solely or mainly about deferring the parsing from the tool
>> stack to the hypervisor, then I'm not at all convinced of the approach
>> (I'd even be tempted to call it backwards).
> 
> The main advantage is that it would be much easier to backport new
> parameters like the xpti per-domain one. No need to bump sysctl/domctl
> interface versions for that.

Additions to sysctl/domctl interfaces don't require such a bump.

> It might be a good idea to support mandatory and optional parameters
> in the guest config. Optional parameters not supported by the hypervisor
> would then be ignored instead of leading to failure at guest creation
> time.

Except that over time opinions may change what is supposed to
be optional vs mandatory.

Jan



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