Re: [Qemu-block] [Qemu-devel] [PATCH 12/18] block-qdict: Clean up qdict_crumple() a bit

[Markus Armbruster]

Kevin Wolf <address@hidden> writes:

> Am 12.06.2018 um 14:58 hat Markus Armbruster geschrieben:
>> When you mix scalar and non-scalar keys, whether you get an "already
>> set as scalar" or an "already set as dict" error depends on qdict
>> iteration order.  Neither message makes much sense.  Replace by
>> ""Cannot mix scalar and non-scalar keys".  This is similar to the
>> message we get for mixing list and non-list keys.
>> 
>> I find qdict_crumple()'s first loop hard to understand.  Rearrange it
>> and add a comment.
>> 
>> Signed-off-by: Markus Armbruster <address@hidden>
>
> To be honest, I found the old version of the loop more obvious.
>
>>  qobject/block-qdict.c | 42 +++++++++++++++++++++---------------------
>>  1 file changed, 21 insertions(+), 21 deletions(-)
>> 
>> diff --git a/qobject/block-qdict.c b/qobject/block-qdict.c
>> index a4e1c8d08f..35e9052816 100644
>> --- a/qobject/block-qdict.c
>> +++ b/qobject/block-qdict.c
>> @@ -403,7 +403,7 @@ static int qdict_is_list(QDict *maybe_list, Error **errp)
>>  QObject *qdict_crumple(const QDict *src, Error **errp)
>>  {
>>      const QDictEntry *ent;
>> -    QDict *two_level, *multi_level = NULL;
>> +    QDict *two_level, *multi_level = NULL, *child_dict;
>>      QObject *dst = NULL, *child;
>>      size_t i;
>>      char *prefix = NULL;
>> @@ -422,29 +422,29 @@ QObject *qdict_crumple(const QDict *src, Error **errp)
>>          }
>>  
>>          qdict_split_flat_key(ent->key, &prefix, &suffix);
>> -
>>          child = qdict_get(two_level, prefix);
>> +        child_dict = qobject_to(QDict, child);
>> +
>> +        if (child) {
>> +            /*
>> +             * An existing child must be a dict and @ent must be a
>> +             * dict member (i.e. suffix not null), or else @ent
>> +             * clashes.
>> +             */
>> +            if (!child_dict || !suffix) {
>> +                error_setg(errp,
>> +                           "Cannot mix scalar and non-scalar keys");
>> +                goto error;
>> +            }
>> +        } else if (suffix) {
>> +            child_dict = qdict_new();
>> +            qdict_put(two_level, prefix, child_dict);
>> +        } else {
>> +            qdict_put_obj(two_level, prefix, qobject_ref(ent->value));
>> +        }
>
> At least, can you please move the else branch to the if below so that
> the addition of the new entry is symmetrical for both scalars and dicts?
> As the code is, it mixes the conflict check, creation of the child dict
> and addition of scalars (but not to the child dict) in a weird way in a
> single if block.
>
> Or maybe organise it like this:
>
> if (child && !(child_dict && suffix)) {
>     error
> }
>
> if (suffix) {
>     if (!child_dict) {
>         create it
>         add it to two_level
>     }
>     add entry to child_dict
> } else {
>     add entry to two_level
> }

Fleshing out...

        if (child && !child_dict) {
            /*
             * @prefix already exists and it's a non-dictionary,
             * i.e. we've seen a scalar with key @prefix.  The same
             * key can't occur twice, therefore suffix must be
             * non-null.
             */
            assert(suffix);
            /*
             * @ent has key @address@hidden, but we've already seen
             * key @prefix: clash.
             */
            error_setg(errp, "Cannot mix scalar and non-scalar keys");
            goto error;
        }

        if (suffix) {
            if (!child_dict) {
                child_dict = qdict_new();
                qdict_put(two_level, prefix, child_dict);
            }
            qdict_put_obj(child_dict, suffix, qobject_ref(ent->value));
        } else {
            assert(!child);
            qdict_put_obj(two_level, prefix, qobject_ref(ent->value));
        }

Okay?