Re: [PATCH 4/5] python: qmp_shell: add -e/--exit-on-error option

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Feb 23, 2022 at 10:41:11AM -0500, John Snow wrote:
> On Wed, Feb 23, 2022 at 10:27 AM Daniel P. Berrangé <berrange@redhat.com> wrote:
> >
> > On Wed, Feb 23, 2022 at 10:22:11AM -0500, John Snow wrote:
> > > On Mon, Feb 21, 2022 at 10:55 AM Damien Hedde
> > > <damien.hedde@greensocs.com> wrote:
> > > >
> > > > This option makes qmp_shell exit (with error code 1)
> > > > as soon as one of the following error occurs:
> > > > + command parsing error
> > > > + disconnection
> > > > + command failure (response is an error)
> > > >
> > > > _execute_cmd() method now returns None or the response
> > > > so that read_exec_command() can do the last check.
> > > >
> > > > This is meant to be used in combination with an input file
> > > > redirection. It allows to store a list of commands
> > > > into a file and try to run them by qmp_shell and easily
> > > > see if it failed or not.
> > > >
> > > > Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
> > >
> > > Based on this patch, it looks like you really want something
> > > scriptable, so I think the qemu-send idea that Dan has suggested might
> > > be the best way to go. Are you still hoping to use the interactive
> > > "short" QMP command format? That might be a bad idea, given how flaky
> > > the parsing is -- and how we don't actually have a published standard
> > > for that format. We've *never* liked the bad parsing here, so I have a
> > > reluctance to use it in more places.
> > >
> > > I'm having the naive idea that a script file could be as simple as a
> > > list of QMP commands to send:
> > >
> > > [
> > >     {"execute": "block-dirty-bitmap-add", "arguments": { ... }},
> > >     ...
> > > ]
> >
> > I'd really recommend against creating a new format for the script
> > file, especially one needing opening & closing  [] like this, as
> > that isn't so amenable to dynamic usage/creation. ie you can't
> > just append an extcra command to an existing file.
> >
> > IMHO, the "file" format should be identical to the result of
> > capturing the socket data off the wire. ie just a concatenation
> > of QMP commands, with no extra wrapping / change in format.
> >
> 
> Eugh. That's just so hard to parse, because there's no off-the-shelf
> tooling for "load a sequence of JSON documents". Nothing in Python
> does it. :\

It isn't that hard if you require each JSON doc to be followed by
a newline.

Feed one line at a time to the JSON parser, until you get a complete
JSON doc, process that, then re-init the parser and carry on feeding
it lines until it emits the next JSON doc, and so on.


Regards,
Daniel
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