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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.09.18 at 13:10, <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).
> 
> So lets look what would be needed for adding something like the
> per-domain xpti parameter using binary interfaces:
> 
> 1 an extension of some domctl interface, maybe bumping of the domctl
>   interface version
> 2 adding the logic to domctl handling
> 3 adding libxc support
> 4 adding libxl support
> 5 adding a new xl sub-command
> 6 adding domain config support
> 7 adding documentation
> 
> With my approach only 2 (in a modified form, parameter handling instead
> of domctl, but comparable in the needed effort) and 7 are needed.
> 
> So once the framework is in place it is _much_ easier to add new
> features.

All the above would hold if the individual options were expressed as
e.g. flags in an extensible bit vector.

Jan



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