On Wed, Feb 23, 2022 at 10:44 AM Daniel P. Berrangé <berra...@redhat.com> wrote:
>
> 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 <berra...@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.he...@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.he...@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.
>
There's two interfaces in Python:
(1) json.load(), which takes a file pointer and either returns a
single, complete JSON document or it raises an Exception. It's not
useful here at all.
(2) json.JSONDecoder().raw_decode(strbuf), which takes a string buffer
and returns a 2-tuple of a JSON Document and the position at which it
stopped decoding.
The second is what we need here, but it does require buffering the
entire file into a string first, and then iteratively calling it. It
feels like working against the grain a little bit. We also can't use
the QAPI parser, as that parser has intentionally removed support for
constructs we don't use in the qapi schema language. Boo. (Not that I
want more non-standard configuration files like that propagating,
either.)
It would be possible to generate a JSON-Schema document to describe a
script file that used a containing list construct, but impossible for
a concatenation of JSON documents. This is one of the reasons I
instinctively shy away from non-standard file formats, they tend to
cut off support for this sort of thing.
Wanting to keep the script easy to append to is legitimate. I'm keen
to hear a bit more about the use case here before I press extremely
hard in any given direction, but those are my impulses here.
--js
