Re: [Qemu-devel] [PATCH v4 0/3] chardev: Add -qmp-pretty

[Markus Armbruster]

Max Reitz <address@hidden> writes:

> On 2014-11-28 at 16:55, Markus Armbruster wrote:
>> Copying Luiz.
>>
>> Max Reitz <address@hidden> writes:
>>
>>> This series does not add new functionality. Adding a QMP monitor with
>>> prettily formatted JSON output can be done as follows:
>>>
>>> $ qemu -chardev stdio,id=mon0 -mon chardev=mon0,mode=control,pretty=on
>>>
>>> However, this is rather cumbersome, so this series (its first patch)
>>> adds a shortcut in the form of the new command line option -qmp-pretty.
>>>
>>> Since the argument given to a monitor command line option (such as -qmp)
>>> is parsed depending on its prefix and probably also depending on the
>>> current phase of the moon, this is cleaner than trying to add a "switch"
>>> to -qmp itself (in the form of "-qmp stdio,pretty=on").
>> Yet another "convenience" option *groan*
>>
>> Why can't we simply make -qmp set pretty=on and be done with it?
>> It's a convenience option, i.e. meant for humans, and why would humans
>> *not* want pretty=on?
>
> Well, pretty=on produces really long output. I prefer short output if
> I don't expect to run commands like query-block which are completely
> unreadable with pretty=off.
>
> I personally had a really bad taste when I saw that I couldn't modify
> -qmp somehow to get it to set pretty=on optionally. But then, after
> having implemented -qmp-pretty in basically five lines (the "case"
> statement for that option and the qemu_opt_set_bool() in
> monitor_parse()), I could send the series with a clear
> conscience. It's not that there's a new convenience option which is
> really bad to maintain and will break after the first gentle blow, as
> it reuses all the code paths from -qmp, which we will keep anyway.

The implementation complexity doesn't worry me.  I dislike the interface
complexity.  We're stuck with two sugar options around -mon, but adding
a *third* is pushing it too far for me.

> Since this is only in block-next, I wouldn't object to it being
> dropped and making pretty=on the default for -qmp, in principle. But I
> personally like having a convenience pretty=off option, too, because I
> as a human often actually don't want pretty=on.

-set mon.compat_monitor0.pretty=off  ;-P

Alternatively, define a pretty and an ugly monitor in a configuration
file, and connect to the one you want:

[chardev "qmp"]
  backend = "socket"
  path = "sock-qmp"
  server = "on"
  wait = "off"

[mon "qmp"]
  mode = "control"
  chardev = "qmp"
  pretty = "off"

[chardev "qmp-pretty"]
  backend = "socket"
  path = "sock-qmp-pretty"
  server = "on"
  wait = "off"

[mon "qmp-pretty"]
  mode = "control"
  chardev = "qmp-pretty"
  pretty = "on"

Alternatively^2, create a QMP command to toggle prettiness.