Re: [Qemu-devel] [PATCH 09/27] qdict: Introduce qdict_rename_keys()

[Eric Blake <eblake@redhat.com>]

On 02/08/2018 01:23 PM, Kevin Wolf wrote:
> A few block drivers will need to rename .bdrv_create options for their
> QAPIfication, so let's have a helper function for that.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   include/qapi/qmp/qdict.h |  6 ++++++
>   qobject/qdict.c          | 30 ++++++++++++++++++++++++++++++
>   2 files changed, 36 insertions(+)

Again, unit test coverage?

> +/**
> + * qdict_rename_keys(): Rename keys in qdict according to the replacements
> + * specified in the array renames. The array must be terminated by an entry
> + * with from = NULL.
> + *
> + * Returns true for success, false in error cases.
> + */
> +bool qdict_rename_keys(QDict *qdict, const QDictRenames *renames, Error **errp)
> +{
> +    QObject *qobj;
> +
> +    while (renames->from) {
> +        if (qdict_haskey(qdict, renames->from)) {
> +            if (qdict_haskey(qdict, renames->to)) {

Depending on how efficient qdict_haskey() is, this is a lot of looping. 
Good thing our lists aren't so large that we'd notice the effects of 
cubic scaling (I count O(m*n*n), where m is renames length, and n is 
worst-case performance of qdict_haskey).  Definitely not worth the 
effort of more code to try and have a more efficient algorithm in 
large-term scaling but which hurts performance with increased overhead 
on small lists.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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