"Dr. David Alan Gilbert" <dgilb...@redhat.com> writes:
> * 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?
Also fix the typo in the title "hmp: Simplify qom_set": it's qom-set.
Reviewed-by: Markus Armbruster <arm...@redhat.com>
