Re: [PATCH v2] btrfs-progs: device stats: add json output format

[David Sterba <dsterba@suse.cz>]

On Sun, Oct 04, 2020 at 11:25:57AM +0000, Sidong Yang wrote:
> Add supports for json formatting, this patch changes hard coded printing
> code to formatted print with output formatter. Json output would be
> useful for other programs that parse output of the command. but it
> changes the text format.
> 
> Example text format:
> 
> device:                 /dev/vdb
> write_io_errs:          0
> read_io_errs:           0
> flush_io_errs:          0
> corruption_errs:        0
> generation_errs:        0
> 
> Example json format:
> 
> {
>   "__header": {
>     "version": "1"
>   },
>   "device-stats": {
>     "/dev/vdb": {
>       "device": "/dev/vdb",
>       "write_io_errs": "0",
>       "read_io_errs": "0",
>       "flush_io_errs": "0",
>       "corruption_errs": "0",
>       "generation_errs": "0"
>     }
>   },
> }

The overall structure looks good, ie. the separate object 'device-stats'
and then the contents. For that the device id should be either key to a
map, or we can put it into an array (where device id must be present
too).

A check if the format is usable you can try to write a sample tool that
parses some of the data and prints them. So eg. using python or jq and
print stats of device 1. Which points out that device id is missing for
example.