12:09 a.m.
On Thu, Mar 20, 2014 at 10:12:43PM +0800, Amos Kong wrote:
On Tue, Mar 11, 2014 at 10:04:56AM +0100, Markus Armbruster wrote:
> Eric Blake <eblake(a)redhat.com> writes:
>
> > On 03/07/2014 02:54 AM, Markus Armbruster wrote:
> >> Eric Blake <eblake(a)redhat.com> writes:
> >>
> >>> On 03/05/2014 07:36 PM, Amos Kong wrote:
> >>>> vm_config_groups[] only contains part of the options which have
> >>>> argument, and all options which have no argument aren't added
> >>>> to vm_config_groups[]. Current query-command-line-options only
> >>>> checks options from vm_config_groups[], so some options will
> >>>> be lost.
> >>>>
> >
> >> Example: -device takes unspecified parameters. -cdrom doesn't take
> >> parameters, it takes a file name. Yet, the command reports the same
> >> for both: "parameters": [], "argument": true.
> >>
> >> Looks like we need a tri-state: option takes no argument, QemuOpts
> >> argument, or other argument.
> >
> > I don't buy that. '-cdrom filename' could easily be re-written [in
a
> > future qemu version] to use QemuOpts with an implied parameter name
> > (we've done that elsewhere, such as for '-machine'). In other
words, I
> > think we could make it become shorthand for '-cdrom file=filename', at
> > which point the QemuOpts spelling is available and would now show up as
> > "parameters":[{"name":"file"...}]. Thus, in
converting -cdrom to
> > QemuOpts, we can still maintain command-line back-compat, while making
> > the query-command-line-options output more featureful. In other words,
> > _for now_ it takes unspecified parameters, and the fact that it is only
> > a single parameter in the form 'filename' rather than a more typical
> > parameter 'file=filename' is not a show-stopper.
>
> Incompatible change for funny filenames: -cdrom you,break=me.
>
> Besides breaking funny filenames, we'd also buy ourselves some stupid
> -readconfig / -writeconfig trouble. Let me explain.
>
> -cdrom F is effectively sugar for "-drive media=cdrom,index=2,file=FF",
> where FF is F with comma doubled.
>
> -writeconfig writes out desugared QemuOpts. Therefore, "-cdrom r7.iso"
> gets written as
>
> [drive]
> media = "cdrom"
> index = "2"
> file = "r7.iso"
>
> which -readconfig can read.
>
> If we convert -cdrom to QemuOpts, it gets written out like this:
>
> [cdrom]
> file = "r7.iso"
>
> If we continue to desugar it, it'll *also* get written out as before.
> Either we *delete* the sugared QemuOpts to avoid duplication, or we
> *stop* desugaring. The latter breaks -readconfig of existing
> configuration files, and complicates the code reading configuration from
> QemuOpts.
>
> I don't think any of the old non-QemuOpts options that have become sugar
> for newer, more flexible QemuOpts options should be converted to
> QemuOpts.
>
> > So your idea of a tri-state (QemuOpts, no argument, or other argument)
> > doesn't add anything - any option that takes "other argument"
could be
> > converted to take QemuOpts, and from the command line, we can't tell the
> > difference from whether something was implemented by QemuOpts, only by
> > whether we have introspection on what the argument consists of.
>
> I doubt we can convert all existing options to QemuOpts without breaking
> backward compatibility and complicating the code.
>
> > Meanwhile, it DOES point out that our use of implicit argument in
> > QemuOpts ought to be exposed to the introspection mechanism, for
> > introspection to be fully descriptive. That is, maybe we should modify
> > our introspection to add a new 'implied-name':
> >
> > ##
> > # @CommandLineParameterInfo:
> > #
> > ...
> > # @implied-name: #optional, if present and true, the parameter can be
> > # specified as '-option value' instead of the preferred
> > # spelling of '-option name=value' (since 2.0)
> > # Since 1.5
> > { 'type': 'CommandLineParameterInfo',
> > 'data': { 'name': 'str',
> > 'type': 'CommandLineParameterType',
> > '*help': 'str', '*implied-name':
'bool' } }
reply-myself
How can we get this information? it's not good to rely on the
help message.
And the parameters [] only have content when the option have a non-NULL desc
table, so we always just return a NULL parameters list, the 'implied-name'
information will be lost.
I'm wrong, 'implied-name' is attribute of parameter, it's stored in
QemuOptsList.implied_opt_name.
I will add this filed in V6.
I thinks Markus's suggestion is fine, we can use tri-state
(no-arg,
unsuecified-para-arg, no-para-arg).
Thanks, Amos
> The only use for implied-name I can think of is interpreting a
user's
> command line. Is that a real use case?
> >>
> >> parameters is [] unless it's a QemuOpts argument. Then it lists
the
> >> recognized parameters.
> >
> > This part is still true. When parameters[] is non-empty, it is a
> > QemuOpts and we know all recognized parameters (well, more precisely,
> > the subset of QemuOpts that were explicitly called out - given your
> > point 2 about the mess of -drive); when it is empty, then all we know is
> > whether the argument is a boolean or takes unspecified arguments (where
> > the conversion of those unknown arguments to QemuOpts will be what
> > finally lets us introspect the format of those unknown arguments).
>
> QemuOpts argument with only unspecified parameters is not the same as
> non-QemuOpts argument. I don't think conflating the two is useful.