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?