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

[Damien Hedde <damien.hedde@greensocs.com>]

On 2/23/22 17:43, Damien Hedde wrote:
> 
> 
> On 2/23/22 16:44, Daniel P. Berrangé 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 
>>> <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 don't really care of the command format. I was just using the one 
> expected by qmp-shell to avoid providing another script.
> I think it's better not to use some standard syntax like json.
I wanted to say the opposite: it's best to use json.
> As long as we can store the commands into a file and tests them easily, 
> it's ok. The crucial feature is the "stop as soon something unexpected 
> happens" so that we can easily spot an issue.
>>>>>
>>>>> 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 used this format at some point because it's so trivial to feed into 
> the QMP tools. Even used a yaml version of that to get the "human 
> readability" that goes with it.
> 
>>>>
>>>> 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.
>>
> 
> I agree it's doable. I can look into that.
> 
> It makes me think that I've managed to modify the chardev 'file' backend
> a few months ago so that it can be used with an input file on the cli. 
> This allowed to give such raw qmp file directly with the -qmp option 
> instead of using an intermediate socket and a script issuing the same file.
> But I gave up with this approach because then it can't stop if a command 
> failed without hacking into the receiving side in qemu.
> 
> -- 
> Damien
> 
> 
>