Re: [Qemu-devel] help parsing qemu options

[Markus Armbruster]

"Gabriel L. Somlo" <address@hidden> writes:

> Hi,
>
> Assuming I'm trying to add a new command line option to qemu in vl.c:
>
> ...
>
> static QemuOptsList qemu_foo_opts = {
>     .name = "foo",
>     .implied_opt_name = "name",
>     .head = QTAILQ_HEAD_INITIALIZER(qemu_foo_opts.head),
>     .desc = {
>         {
>             .name = "name",
>             .type = QEMU_OPT_STRING,
>         }, {
>             .name = "file",
>             .type = QEMU_OPT_STRING,
>         },
>         { /* end of list */ }
>     },
> };
>
> ...
>
> main() {
>
>     ...
>     qemu_add_opts(&qemu_foo_opts);
>
>     ...
>
>     /* second pass of option parsing */
>     ...
>     for(;;) {
>         ...
>         switch(popt->index) {
>             ...
>
>         case QEMU_OPTION_foo:
>             opts = qemu_opts_parse(qemu_find_opts("foo"), optarg, 0);
>             if (!foo_option_add(qemu_opt_get(opts, "name"),
>                                 qemu_opt_get(opts, "file"))) {
>                 fprintf(stderr, "invalid foo entry config %s\n", optarg);
>                 exit(1);
>             }
>             break;
>
>     ...
> }
>
>
> Somewhere else in the source I have
>
> bool foo_option_add(const char *name, const char *file) {
>
>     if (/* everything OK */) {
>         return true;
>     }
>
>     return false;
> }    

Looks sane so far.

> 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.