Re: ImageInfo oddities regarding compression

[Markus Armbruster <armbru@redhat.com>]

Kevin Wolf <kwolf@redhat.com> writes:

> Am 27.11.2020 um 13:21 hat Markus Armbruster geschrieben:
>> >> I fell down this (thankfully shallow) rabbit hole because we also have
>> >> 
>> >>     { 'enum': 'MultiFDCompression',
>> >>       'data': [ 'none', 'zlib',
>> >>                 { 'name': 'zstd', 'if': 'defined(CONFIG_ZSTD)' } ] }
>> >> 
>> >> I wonder whether we could merge them into a common type.
>> 
>> Looks like we could: current code would never report the additional
>> value 'none'.  Introspection would show it, though.  Seems unlikely to
>> cause trouble.  Observation, not demand.
>
> Forgot to comment on this one...
>
> Technically we could probably, but would it make sense? Support for
> compression formats has to be implemented separately for both cases, so
> that they currently happen to support the same list is more of a
> coincidence.
>
> If we ever add a third compression format to qcow2, would we add the
> same format to migration, too, or would we split the schema into two
> types again?

I figure if a compression method is worth adding to one, it's probably
worth adding to the other.

Having two separate enums isn't too bad.  A third has been proposed[*],
but I hope we can reuse migration's existing enum there.


[*] [PATCH 1/6] migration: Add multi-thread compress method