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

[Juergen Gross <jgross@suse.com>]

On 18/09/18 13:20, Jan Beulich wrote:
>>>> On 18.09.18 at 13:10, <jgross@suse.com> wrote:
>> On 18/09/18 12:32, Jan Beulich wrote:
>>>>>> On 18.09.18 at 08:02, <jgross@suse.com> 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.

Who would translate the new option into a bit vector? This would be the
tools (libxc/libxl/xl), so those need to be modified for each new bit.


Juergen

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