Re: [Qemu-devel] help parsing qemu options

[Gabriel L. Somlo]

On Wed, Mar 11, 2015 at 08:40:46AM -0400, Gabriel L. Somlo wrote:
> On Wed, Mar 11, 2015 at 12:59:40PM +0100, Kevin Wolf wrote:
> > 
> > def_value_str exists in the current codebase, and it seems to take
> > precedence when a different default is specified by the caller.
> 
> So I've now added .def_value_str fields:
> 
> static QemuOptsList qemu_foo_opts = {
>     .name = "foo",
>     .head = QTAILQ_HEAD_INITIALIZER(qemu_foo_opts.head),
>     .desc = {
>         {
>             .name = "name",
>             .type = QEMU_OPT_STRING,
>             .def_value_str = "abc",
>         }, {
>             .name = "file",
>             .type = QEMU_OPT_STRING,
>             .def_value_str = "xyz",
>         },
>         { /* end of list */ }
>     },
> };
> 
> but "-foo name,file" still results in qemu_opt_get(opts, "name")
> returning "on", rather than "abc". Is that a bug, or am I missing
> something, or doing something wrong ?

Specifically, in qemu_opt_get() (in util/qemu-option.c:311)
desc->def_value_str is only used if qemu_opt_find() returns NULL,
which in my case does NOT happen ("on" is returned instead).

That, in turn, probably happens because opts_do_parse()
(in util/qemu-options.c:776) assumes that "option without value"
is "probably a flag" :)

Not sure we'd want to mess with that assumption, but that most likely
means I don't get to use .def_value_str the way I thought I could :)

Thanks,
--Gabriel