* Markus Armbruster (arm...@redhat.com) wrote:
> "Dr. David Alan Gilbert" <dgilb...@redhat.com> writes:
>
> > * Philippe Mathieu-Daudé (phi...@redhat.com) wrote:
> >> On 5/20/20 5:11 PM, Dr. David Alan Gilbert (git) wrote:
> >> > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
> >> >
> >> > Simplify qom_set by making it use qmp_qom_set and the JSON parser.
> >> >
> >> > Note that qom-set likes JSON strings quoted with ' not ", e.g.:
> >> >
> >> > (qemu) qom-get /machine smm
> >> > "auto"
> >> > (qemu) qom-set /machine smm 'auto'
> >>
> >> Will I get this output using "?
> >>
> >> (qemu) qom-set /machine smm "auto"
> >> Error: Expecting a JSON value
> >
> > The error you get is:
> >
> > (qemu) qom-set /machine smm "auto"
> > Error: JSON parse error, invalid keyword 'auto'
> >
> > I think, having seen alphanumerics, it's expecting a keyword;
> > i.e. a true/false making a bool, or a null.
>
> The command parses its argument as JSON.
>
> Before we get there, the HMP core extracts the argument from the line of
> input. The extraction is guided by the command's .args_type, in this
> case the 's' in "value:s" in
>
> {
> .name = "qom-set",
> .args_type = "path:s,property:s,value:s",
> [...]
> },
>
> monitor/monitor-internal.h documents type code 's' as
>
> * 's' string (accept optional quote)
>
> The implementation boils down to:
>
> 1. Skip whitespace.
>
> 2. If looking at '"', get the string enclosed in '"', with C-like escape
> sequences \n, \r, \\, \', \".
>
> 3. Else, get the string up to the next whitespace.
>
> See get_str().
>
> Therefore, argument "auto" is the same as auto. Parsing auto as JSON
> duly fails.
>
> Argument 'auto' works, but only because qobject_from_json() recognizes
> single-quoted strings. This is as extension over RFC 8259.
>
> Using single quotes falls apart when you want to pass something
> containing whitespace. Then you'd have to use
>
> "\"ugly and unintuitive\""
>
> or, again relying on the extension
>
> "'ugly and unintuitive'"
>
> There's a better way, and Paolo pointed it out in
>
> Subject: Re: [RFC PATCH] qom: Implement qom-get HMP command
> Date: Thu, 21 May 2020 16:24:12 +0200
> Message-ID: <2c148331-78ae-31f7-8702-d65c37a09...@redhat.com>
>
> Use argument type 'S'. Documented as
>
> * 'S' it just appends the rest of the string (accept optional quote)
>
> but the parenthesis is confusing. It really just skips whitespace, then
> extracts the remainder of the line. Can't do string with leading
> whitespace, but that's just fine for us.
Yep, thanks - I spotted Paolo's response but thanks for the deeper
explanation.
With that would you give me a Review-by?
Dave
> Please squash in:
>
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index 250ddae54d..28256209b5 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -1806,7 +1806,7 @@ ERST
>
> {
> .name = "qom-set",
> - .args_type = "path:s,property:s,value:s",
> + .args_type = "path:s,property:s,value:S",
> .params = "path property value",
> .help = "set QOM property",
> .cmd = hmp_qom_set,
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
