Re: [Qemu-devel] help parsing qemu options

[Gabriel L. Somlo]

On Tue, Mar 10, 2015 at 09:40:09AM +0100, Markus Armbruster wrote:
> "Gabriel L. Somlo" <address@hidden> writes:
> > Assuming the above is correct (and that the appropriate glue is added
> > to qemu-options.hx to tie "-foo name=abc,file=xyz" to QEMU_OPTION_foo),
> > I'm wondering about preventing "name" and "file" from being turned
> > into Booleans should their arguments be omitted on the command line.
> >
> > To clarify:
> >
> > -foo abcxyz   results in a parse error generated by qemu_opts_parse()
> >               which is as it should be
> >
> > -foo file=abc,name=xyz   results in a call to foo_option_add("xyz", "abc")
> >                          which is the desired behavior
> >
> > -foo file=,name=   results in a call to foo_option_add("", "")
> >                    which is also OK, as I can sanity-check my
> >                    arguments from within foo_option_add()
> >
> > However,
> >
> > -foo file,name    results in a call to foo_option_add("on", "on")
> >                   i.e., in the absence of string values, both
> >                   "file" and "name" are converted into Booleans
> >                   and given the string value "on" by qemu_opts_parse()
> >                   which is NOT what I want, and I'm wondering if
> >                   that behavior can somehow be turned off for
> >                   any given QemuOptsList ?
> >
> > I guess I could be looking for a file named "on" in the current
> > directory, and attempt to use the value "on" to insert the object
> > from the given file (and fail if no file named "on" could be found,
> > but this is not as clean as I would like it to be, and I'm wondering
> > if there's a better way).
> 
> Reproduced:
> 
>     $ upstream-qemu -nodefaults -S -display vnc=:0 -monitor stdio -name 
> process=foo,guest
>     QEMU 2.2.50 monitor - type 'help' for more information
>     (qemu) info name
>     on
> 
> QemuOpts is baroque.
> 
> No, you can't switch it off.  I'm afraid adding such a switch is not a
> good idea, because it would make QemuOpts even more baroque.
> 
> Perhaps we can limit the convenience syntax "omitted value means =on" to
> boolean options.  Could be hairy, because .desc can be empty, which
> defers part of the checking until later.

Maybe adding a .default field to .desc, so if the parameter is defined
but no value is assigned, the .default value (which could be NULL) is
used instead of always defaulting to "on" ?

No idea if that'd be worth it though, I was just wondering if there's
already a mechanism controlling whether fallback-to-bool is a (per
QemuOptsList struct) tunable option, which I now know it is not :)

Thanks much,
--Gabriel