[PATCH v4 4/4] tests: add check for decoding of netfilter subsystem

[Dmitry V. Levin]

On Sun, Mar 11, 2018 at 09:43:53AM +0800, Chen Jingpiao wrote:
> On 03/11 03:48, Dmitry V. Levin wrote:
[...]
> > In other words, NFNL_SUBSYS_COUNT provided by kernel headers is unreliable
> > and shouldn't be used, I think it has to be removed from
> > xlat/nl_netfilter_subsys_ids.in as well.
> 
> I can not find an existing way to remove the condition from xlat/*.h.
> xlat/gen.sh only have print_xlat and cond_xlat to generate xlat array.
> Should I add a directive?

Well, you can simply write

#undef NFNL_SUBSYS_COUNT
#define NFNL_SUBSYS_COUNT       12
NFNL_SUBSYS_COUNT

but NFNL_SUBSYS_COUNT is not a symbol with some constant value: it changes
with time, so what's the use of printing it in symbolic form?

> ps:
> Is the same problem exist in other counter symbols in xlat/*.in?
> (I do the research, not found.)

I haven't investigated it.  We might have more issues of this nature,
but if we do, then they are not covered by tests.

> > For netlink_netfilter.c purposes I'd recommend to use something like
> > (subsys_id > nl_netfilter_subsys_ids[ARRAY_SIZE(nl_netfilter_subsys_ids)
> - 1].val)
> > instead of subsys_id >= NFNL_SUBSYS_COUNT).
> 
> If I have removed kernel header's NFNL_SUBSYS_COUNT value from
> xlat/nl_netfilter_subsys_ids.in.
> Why can't we use subsys_id >= NFNL_SUBSYS_COUNT?

I wonder whether it's a good idea to check against NFNL_SUBSYS_COUNT?
Wouldn't it be more future-proof to invoke decode_nlattr for any
subsys_id?


-- 
ldv
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