Re: [PATCH 0/7] btrfs-progs: implement json output for subvolume subcommands

[David Sterba <dsterba@suse.cz>]

On Fri, Aug 18, 2023 at 08:39:58PM +0200, Christoph Heiss wrote:
> First of, thanks for the review & merging right away!
> On Thu, Aug 17, 2023 at 09:34:37PM +0200, David Sterba wrote:
> >
> > On Sun, Aug 13, 2023 at 11:44:55AM +0200, Christoph Heiss wrote:
> > > [..]
> >
> > Thanks. There are a few things regarding the json output that are still
> > to be figured out and to set examples to follow. The plain and json
> > output does not match 1:1 in the printed information, here the
> > 'top level' does not need to be in the json output or there could be
> > more subvolume related info in the map.
> 
> > The textual output is unfortunatelly parsed by many tools nowadays so
> > we can't change the format. With json it's easier to filter out the
> > interesting data so "more is better" in this case.
> Right, makes sense. I skimmed through your additional commits on top,
> e.g. the null uuid thing. So all "optional" fields should rather be
> `null` than missing.
> 
> >
> > The formatter is designed in a way to allow plain text and json to be
> > printed by the same lines of code but this is namely for line oriented
> > output, like 'subvolume show'.
> Yeah, I figured that after looking at it a bit more - that's why I
> decided to leave most of the stuff as-is for now.
> 
> > [..]
> >
> > I'll put some guidelines to the documentation, the key naming must be
> > unified, e.g. 'gen' or 'generation' but there's also 'transid' used in
> > some cases etc.
> >
> > As the json format is also an ABI we need to get it finalized first
> Does it make sense to explicitly document all the possible json outputs
> with all their fields, i.e provide example outputs?

Yes, examples are very useful, all of the commands supporting json
should have coverage in the tests. For startes a command that does not
change the state could just duplicate the one done in test but with
`--format=json'. Then it'll appear in the test logs and is easy to
review or copy elsewhere.

The tests/json-formatter-test.c should cover all the basic stuff, it's
also not complete so it can serve as example provider.

We may want to put the examples into the documentation then it's also
good for understanding, though this coud get out of sync over time.

> > so I'll merge the series but put the actual support for --json option
> > under experimental build.
> Thanks! Makes it easier to improve on it gradually in any case. I will
> send some more patches your way rectifying these things as soon as I get
> to it.

Thanks.