Re: [PATCH v2 25/31] qemu-img: Use user_creatable_process_cmdline() for --object

[Eric Blake <eblake@redhat.com>]

On 2/24/21 7:52 AM, Kevin Wolf wrote:
> This switches qemu-img from a QemuOpts-based parser for --object to
> user_creatable_process_cmdline() which uses a keyval parser and enforces
> the QAPI schema.
> 
> Apart from being a cleanup, this makes non-scalar properties accessible.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  qemu-img.c | 239 ++++++++---------------------------------------------
>  1 file changed, 33 insertions(+), 206 deletions(-)
> 

> @@ -1423,15 +1373,9 @@ static int img_compare(int argc, char **argv)
>          case 'U':
>              force_share = true;
>              break;
> -        case OPTION_OBJECT: {
> -            QemuOpts *opts;
> -            opts = qemu_opts_parse_noisily(&qemu_object_opts,
> -                                           optarg, true);
> -            if (!opts) {
> -                ret = 2;
> -                goto out4;

Our exit status here of 2 on failure appears to be intentional (since we
reserve 0 for identical, 1 for mismatch, >1 for error)...

> -            }
> -        }   break;
> +        case OPTION_OBJECT:
> +            user_creatable_process_cmdline(optarg);
> +            break;

...but becomes 1 here.  Does that matter?

/me goes and tests...

Ouch: with current qemu.git master and none of this series applied:

$ ./qemu-img compare --object foo,id=x /dev/null /dev/null
qemu-img: invalid object type: foo
$ echo $?
1
$ gdb --args ./qemu-img compare --object foo,id=x /dev/null /dev/null
(gdb) b qemu_opts_pars
(gdb) r
(gdb) fin
Run till exit from #0  qemu_opts_parse_noisily (
    list=0x55555578f020 <qemu_object_opts>, params=0x7fffffffd8a8
"foo,id=x",
    permit_abbrev=true) at ../util/qemu-option.c:948
0x00005555555805f9 in img_compare (argc=5, argv=0x7fffffffd480)
    at ../qemu-img.c:1428
1428	            opts = qemu_opts_parse_noisily(&qemu_object_opts,
Value returned is $1 = (QemuOpts *) 0x55555583b4b0
(gdb) p *opts
$3 = {id = 0x5555557a0d58 <qemu_trace_opts+24> "`\264\203UUU", list = 0x51,
  loc = {kind = (unknown: 0x557f08f0), num = 21845,
    ptr = 0x55555578f020 <qemu_object_opts>, prev = 0x0}, head = {
    tqh_first = 0x0, tqh_circ = {tql_next = 0x0, tql_prev = 0x0}}, next = {
    tqe_next = 0x55555583b500, tqe_circ = {tql_next = 0x55555583b500,
      tql_prev = 0x55555583b528}}}
(gdb)

That looks buggy.  qemu_opts_parse_noisily() is NOT returning NULL, but
rather a pointer to something garbage (that id pointing to a garbage
string in the middle of qemu_trace_opts is fishy), and so we've been
exiting with status 1 in spite of the code.

Looks like we'll want a separate patch fixing that first.

>          case OPTION_IMAGE_OPTS:
>              image_opts = true;
>              break;
> @@ -1450,13 +1394,6 @@ static int img_compare(int argc, char **argv)
>      filename1 = argv[optind++];
>      filename2 = argv[optind++];
>  
> -    if (qemu_opts_foreach(&qemu_object_opts,
> -                          user_creatable_add_opts_foreach,
> -                          qemu_img_object_print_help, &error_fatal)) {
> -        ret = 2;
> -        goto out4;

Same deal with return value.  Except here we used &error_fatal (which
forces an exit status of 1 rather than returning), and so never even
reach the ret=2 code.  Looks like we broke that in commit 334c43e2c3,
where we used to pass NULL instead of &error_fatal (although that commit
was in turn fixing another problem).

The rest of this patch looks fine, although maybe
user_creatable_process_cmdline() should be given an 'int status'
parameter for specifying 1 vs. 2 (or any other non-zero value) if we
intend to fix the status of qemu-img compare failures.  (Thankfully,
even though qemu-img check also has a variety of documented return
values other than 1, at least it documented 1 as internal errors and was
already using 1 for --object failures).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org