Re: [libvirt] [PATCH 2/2] qapi: deprecate implicit filters
27.08.2019 23:12, John Snow wrote:
On 8/23/19 5:22 AM, Vladimir Sementsov-Ogievskiy wrote:
> 14.08.2019 13:07, Vladimir Sementsov-Ogievskiy wrote:
>> To get rid of implicit filters related workarounds in future let's
>> deprecate them now.
>
> Interesting, could we deprecate implicit filter without deprecation of unnecessity
of
> parameter? As actually, it's good when this parameter is not necessary, in most
cases
> user is not interested in node-name.
>
https://en.wiktionary.org/wiki/unnecessity -- I am surprised to learn
that this a real word in the language I speak. :)
I assume you're referring to making the optional argument mandatory.
exactly, it's my a bit "google-translate-driven" English)
> Obviously we can do the following:
>
> 1. In 4.2 we deprecate unnecessity, which implies deprecation of implicit filters
> 2. After some releases in 4.x we can drop deprecated functionality, so we drop it
together with
> implicit filters. And, in same release 4.x we return it back (as it's compatible
change :)
> but without implicit filters (so, if filter-node-name not specified, we just create
> explicit filter with autogenerated node-name)
>
> So, effectively we just drop "deprecation mark" together with implicit
filters, which is nice
> but actually confusing.
>
> Instead, we may do
> 1. In 4.2 deprecate
> 2. In 4.x drop optionality together with implicit filters
> 3. In 4.y (y > x of course) return optionality back
>
Ah, I see what you're digging at here now...
> It's a bit safer, but for users who miss releases [4.x, 4.y) it's no
difference..
>
> Or we just write in spec, that implicit filters are deprecated? But we have nothing
about implicit
> filters in spec. More over, we directly write that we have filter, and if parameter
is omitted
> it's node-name is autogenerated. So actually, the fact the filter is hidden when
filter-node-name is
> unspecified is _undocumented_.
>
> So, finally, it looks like nothing to deprecated in specification, we can just drop
implicit filters :)
>
> What do you think?
>
What exactly _IS_ an implicit filter? How does it differ today from an
explicit filter? I assumed the only difference was if it was named or
not; but I think I must be mistaken now if you're proposing leaving the
interface alone entirely.
Are they instantiated differently?
As I understand, the only difference is their BlockDriverState.impicit field, and several
places in code
where we skip implicit filter when trying to find something in a chain starting from a
device.
Hmm, OK, let's see:
1. the only implicit filters are commit_top and mirror_top if user don't specify
filter-node-name.
Where it make sense, i.e., where implicit field used?
2. bdrv_query_info, bdrv_query_bds_stats, bdrv_block_device_info(only when called from
bdrv_query_info), they'll
report filter as top node if we don't mark it implicit.
3. bdrv_refresh_filename, bdrv_reopen_parse_backing, bdrv_drop_intermediate:
I think it's not a problem, just drop special case for implicit fitlers
So, seems the only real change is query-block and query-blockstats output when mirror or
commit is started
without specifying filter-node-name (filter would be on top)
So, how should we deprecate this, or can we just change it?
--
Best regards,
Vladimir