[V13,2/6] avoid duplication of default value in QemuOpts

According Markus's comments, his patch will move the default value entirely
to QemuOptDesc.

When getting the value of an option that hasn't been set, and
QemuOptDesc has a default value, return that.  Else, behave as
before.

Example: qemu_opt_get_number(opts, "foo", 42)

   If "foo" has been set in opts, return its value.

   Else, if opt's QemuOptDesc has a default value for "foo", return
   that.

   Else, return 42.

   Note that the last argument is useless when QemuOptDesc has a
   default value.  Ugly.  If it bothers us, assert that the argument
   equals the default from QemuOptDesc.

Example: qemu_opt_get(opts, "bar")

   If "bar" has been set in opts, return its value.

   Else, if opt's QemuOptDesc has a default value for "bar", return
   that.

   Else, return NULL.

Signed-off-by: Dong Xu Wang <wdongxu@linux.vnet.ibm.com>
---
 util/qemu-option.c | 58 +++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 40 insertions(+), 18 deletions(-)

Dong Xu Wang <wdongxu@linux.vnet.ibm.com> writes:

> According Markus's comments, his patch will move the default value entirely
> to QemuOptDesc.
>
> When getting the value of an option that hasn't been set, and
> QemuOptDesc has a default value, return that.  Else, behave as
> before.
>
> Example: qemu_opt_get_number(opts, "foo", 42)
>
>    If "foo" has been set in opts, return its value.
>
>    Else, if opt's QemuOptDesc has a default value for "foo", return
>    that.
>
>    Else, return 42.
>
>    Note that the last argument is useless when QemuOptDesc has a
>    default value.  Ugly.  If it bothers us, assert that the argument
>    equals the default from QemuOptDesc.

Last sentence is not 100% clear.  Either change it to "If it bothers us,
we could assert", or implement the assert.  Considering we're at v12, I
recommend the former.

>
> Example: qemu_opt_get(opts, "bar")
>
>    If "bar" has been set in opts, return its value.
>
>    Else, if opt's QemuOptDesc has a default value for "bar", return
>    that.
>
>    Else, return NULL.
>
> Signed-off-by: Dong Xu Wang <wdongxu@linux.vnet.ibm.com>
> ---
>  util/qemu-option.c | 58 +++++++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 40 insertions(+), 18 deletions(-)
>
> diff --git a/util/qemu-option.c b/util/qemu-option.c
> index 57cdd57..4f94000 100644
> --- a/util/qemu-option.c
> +++ b/util/qemu-option.c
> @@ -525,10 +525,28 @@ static QemuOpt *qemu_opt_find(QemuOpts *opts, const char *name)
>      return NULL;
>  }
>  
> +static const QemuOptDesc *find_desc_by_name(const QemuOptDesc *desc,
> +                                            const char *name)
> +{
> +    int i;
> +
> +    for (i = 0; desc[i].name != NULL; i++) {
> +        if (strcmp(desc[i].name, name) == 0) {
> +            return &desc[i];
> +        }
> +    }
> +
> +    return NULL;
> +}
> +
>  const char *qemu_opt_get(QemuOpts *opts, const char *name)
>  {
>      QemuOpt *opt = qemu_opt_find(opts, name);
> -    return opt ? opt->str : NULL;
> +    const QemuOptDesc *desc;
> +    desc = find_desc_by_name(opts->list->desc, name);
> +
> +    return opt ? opt->str :
> +        (desc && desc->def_value_str ? desc->def_value_str : NULL);
>  }
>  

I'd make this function work exactly like the ones that follow:

    if (!opt) {
        desc = find_desc_by_name(opts->list->desc, name);
        if (desc && desc->def_value_str) {
            return desc->def_value_str;
        }
    }
    return opt ? opt->str : NULL;

Matter of taste; no need to respin just for that.

>  bool qemu_opt_has_help_opt(QemuOpts *opts)
> @@ -546,9 +564,15 @@ bool qemu_opt_has_help_opt(QemuOpts *opts)
>  bool qemu_opt_get_bool(QemuOpts *opts, const char *name, bool defval)
>  {
>      QemuOpt *opt = qemu_opt_find(opts, name);
> +    const QemuOptDesc *desc;
>  
> -    if (opt == NULL)
> +    if (opt == NULL) {
> +        desc = find_desc_by_name(opts->list->desc, name);
> +        if (desc && desc->def_value_str) {
> +            parse_option_bool(name, desc->def_value_str, &defval, NULL);

Ignores errors.  Should only happen when somebody sets a bad
desc->def_value_str.  Because those are fixed at compile time, that's a
programming error.  Recommend to assert like this:

            parse_option_bool(name, desc->def_value_str, &defval, &local_err);
            assert(!local_err);

> +        }
>          return defval;
> +    }
>      assert(opt->desc && opt->desc->type == QEMU_OPT_BOOL);
>      return opt->value.boolean;
>  }
> @@ -556,9 +580,15 @@ bool qemu_opt_get_bool(QemuOpts *opts, const char *name, bool defval)
>  uint64_t qemu_opt_get_number(QemuOpts *opts, const char *name, uint64_t defval)
>  {
>      QemuOpt *opt = qemu_opt_find(opts, name);
> +    const QemuOptDesc *desc;
>  
> -    if (opt == NULL)
> +    if (opt == NULL) {
> +        desc = find_desc_by_name(opts->list->desc, name);
> +        if (desc && desc->def_value_str) {
> +            parse_option_number(name, desc->def_value_str, &defval, NULL);

Likewise.

> +        }
>          return defval;
> +    }
>      assert(opt->desc && opt->desc->type == QEMU_OPT_NUMBER);
>      return opt->value.uint;
>  }
> @@ -566,9 +596,15 @@ uint64_t qemu_opt_get_number(QemuOpts *opts, const char *name, uint64_t defval)
>  uint64_t qemu_opt_get_size(QemuOpts *opts, const char *name, uint64_t defval)
>  {
>      QemuOpt *opt = qemu_opt_find(opts, name);
> +    const QemuOptDesc *desc;
>  
> -    if (opt == NULL)
> +    if (opt == NULL) {
> +        desc = find_desc_by_name(opts->list->desc, name);
> +        if (desc && desc->def_value_str) {
> +            parse_option_size(name, desc->def_value_str, &defval, NULL);

Likewise.

> +        }
>          return defval;
> +    }
>      assert(opt->desc && opt->desc->type == QEMU_OPT_SIZE);
>      return opt->value.uint;
>  }
> @@ -609,20 +645,6 @@ static bool opts_accepts_any(const QemuOpts *opts)
>      return opts->list->desc[0].name == NULL;
>  }
>  
> -static const QemuOptDesc *find_desc_by_name(const QemuOptDesc *desc,
> -                                            const char *name)
> -{
> -    int i;
> -
> -    for (i = 0; desc[i].name != NULL; i++) {
> -        if (strcmp(desc[i].name, name) == 0) {
> -            return &desc[i];
> -        }
> -    }
> -
> -    return NULL;
> -}
> -
>  static void opt_set(QemuOpts *opts, const char *name, const char *value,
>                      bool prepend, Error **errp)
>  {