Re: [PATCH 0/5] fix segment fault when parse args

[Thomas Monjalon <thomas@monjalon.net>]

22/03/2023 09:53, Ferruh Yigit:
> On 3/22/2023 1:15 AM, fengchengwen wrote:
> > On 2023/3/21 21:50, Ferruh Yigit wrote:
> >> On 3/17/2023 2:43 AM, fengchengwen wrote:
> >>> On 2023/3/17 2:18, Ferruh Yigit wrote:
> >>>> On 3/14/2023 12:48 PM, Chengwen Feng wrote:
> >>>>> The rte_kvargs_process() was used to parse KV pairs, it also supports
> >>>>> to parse 'only keys' (e.g. socket_id) type. And the callback function 
> >>>>> parameter 'value' is NULL when parsed 'only keys'.
> >>>>>
> >>>>> It may leads to segment fault when parse args with 'only key', this 
> >>>>> patchset fixes rest of them.
> >>>>>
> >>>>> Chengwen Feng (5):
> >>>>>   app/pdump: fix segment fault when parse args
> >>>>>   net/memif: fix segment fault when parse devargs
> >>>>>   net/pcap: fix segment fault when parse devargs
> >>>>>   net/ring: fix segment fault when parse devargs
> >>>>>   net/sfc: fix segment fault when parse devargs
> >>>>
> >>>> Hi Chengwen,
> >>>>
> >>>> Did you scan all `rte_kvargs_process()` instances?
> >>>
> >>> No, I was just looking at the modules I was concerned about.
> >>> I looked at it briefly, and some modules had the same problem.
> >>>
> >>>>
> >>>>
> >>>> And if there would be a way to tell kvargs that a value is expected (or
> >>>> not) this checks could be done in kvargs layer, I think this also can be
> >>>> to look at.
> >>>
> >>> Yes, the way to tell kvargs may lead to a lot of modifys and also break ABI.
> >>> I also think about just set value = "" when only exist key, It could perfectly solve the above segment scene.
> >>> But it also break the API's behavior.
> >>>
> >>
> >> What about having a new API, like `rte_kvargs_process_extended()`,
> >>
> >> That gets an additional flag as parameter, which may have values like
> >> following to indicate if key expects a value or not:
> >> ARG_MAY_HAVE_VALUE  --> "key=value" OR 'key'
> >> ARG_WITH_VALUE      --> "key=value"
> >> ARG_NO_VALUE        --> 'key'
> >>
> >> Default flag can be 'ARG_MAY_HAVE_VALUE' and it becomes same as
> >> `rte_kvargs_process()`.
> >>
> >> This way instead of adding checks, relevant usage can be replaced by
> >> `rte_kvargs_process_extended()`, this requires similar amount of change
> >> but code will be more clean I think.
> >>
> >> Do you think does this work?
> > 
> > Yes, it can work.
> > 
> > But I think the introduction of new API adds some complexity.
> > And a good API definition could more simpler.
> > 
> 
> Other option is changing existing API, but that may be widely used and
> changing it impacts applications, I don't think it worth.

I've planned a change in kvargs API 5 years ago and never did it:
From doc/guides/rel_notes/deprecation.rst:
"
* kvargs: The function ``rte_kvargs_process`` will get a new parameter
  for returning key match count. It will ease handling of no-match case.
"

> Of course we can live with as it is and add checks to the callback
> functions, although I still believe a new 'process()' API is better idea.