Re: [Qemu-devel] [PATCH 2/5] tests: Enhance qobject output to cover partial visit

[Markus Armbruster <armbru@redhat.com>]

Eric Blake <eblake@redhat.com> writes:

> Add a test that proves (at least when run under valgrind) that
> we are correctly handling allocated memory even when a visit
> is aborted in the middle for whatever other reason.
>
> See commit f24582d "qapi: fix double free in
> qmp_output_visitor_cleanup()" for a fix that was lacking
> testsuite exposure prior to this patch.
>
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>  tests/test-qobject-output-visitor.c | 46 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 45 insertions(+), 1 deletion(-)
>
> diff --git a/tests/test-qobject-output-visitor.c b/tests/test-qobject-output-visitor.c
> index 749c540..1e9a5d1 100644
> --- a/tests/test-qobject-output-visitor.c
> +++ b/tests/test-qobject-output-visitor.c
> @@ -1,7 +1,7 @@
>  /*
>   * QObject Output Visitor unit-tests.
>   *
> - * Copyright (C) 2011-2016 Red Hat Inc.
> + * Copyright (C) 2011-2017 Red Hat Inc.
>   *
>   * Authors:
>   *  Luiz Capitulino <lcapitulino@redhat.com>
> @@ -251,6 +251,48 @@ static void test_visitor_out_struct_errors(TestOutputVisitorData *data,
>  }
>
>
> +static void test_visitor_out_partial_visit(TestOutputVisitorData *data,
> +                                           const void *unused)
> +{
> +    /* Various checks that a mid-visit abort doesn't leak or double-free. */
> +    const char *str = "hi";
> +    Error *err = NULL;
> +    UserDefAlternate uda = {
> +        .type = QTYPE_QDICT,
> +        .u.udfu = { .integer = 1,
> +                    .string = (char *) "bye",
> +                    .enum1 = -1 } /* intentionally bad */
> +    };
> +    UserDefAlternate *obj = &uda;
> +
> +    /* Abort within a nested object with no data members */
> +    visit_start_struct(data->ov, NULL, NULL, 0, &error_abort);
> +    visit_start_struct(data->ov, "nested", NULL, 0, &error_abort);
> +    visitor_reset(data);
> +
> +    /* Abort in the middle of a list of strings */
> +    visit_start_list(data->ov, "list", NULL, 0, &error_abort);
> +    visit_type_str(data->ov, NULL, (char **)&str, &error_abort);
> +    visit_type_str(data->ov, NULL, (char **)&str, &error_abort);
> +    visitor_reset(data);
> +
> +    /*
> +     * Abort in the middle of an alternate. Alternates can't be
> +     * virtually visited, so we get to inline the first half of
> +     * visit_type_UserDefAlternate().
> +     */

Not exactly inline.  Perhaps:

       /*
        * Abort in the middle of an alternate.  Since alternates don't
        * support virtual visits, we perform a real one, similar to what
        * visit_type_UserDefAlternate() would do.
        */

Hmm, what would visit_type_UserDefAlternate() do for @uda?  Could we
simply call it here and be done?

I've explored supporting virtual alternate visits, but my solution isn't
quite ready, yet.

> +    visit_start_alternate(data->ov, NULL, (GenericAlternate **)&obj,
> +                          sizeof(uda), &error_abort);
> +    visit_start_struct(data->ov, NULL, NULL, 0, &error_abort);
> +    visit_type_UserDefUnionBase_members(data->ov,
> +                                        (UserDefUnionBase *)&uda.u.udfu,
> +                                        &err);
> +    /* error expected because of bad "enum1" discriminator value */
> +    error_free_or_abort(&err);
> +    visitor_reset(data);
> +}
> +
> +
>  static void test_visitor_out_list(TestOutputVisitorData *data,
>                                    const void *unused)
>  {
> @@ -815,6 +857,8 @@ int main(int argc, char **argv)
>                              &out_visitor_data, test_visitor_out_struct_nested);
>      output_visitor_test_add("/visitor/output/struct-errors",
>                              &out_visitor_data, test_visitor_out_struct_errors);
> +    output_visitor_test_add("/visitor/output/partial-visit",
> +                            &out_visitor_data, test_visitor_out_partial_visit);
>      output_visitor_test_add("/visitor/output/list",
>                              &out_visitor_data, test_visitor_out_list);
>      output_visitor_test_add("/visitor/output/any",