Re: [PATCH v4 2/3] Do error handling if __build_packet_message fails

[Marcelo Ricardo Leitner <mleitner@redhat.com>]

On 04-11-2014 17:04, Pablo Neira Ayuso wrote:
> On Tue, Nov 04, 2014 at 04:52:31PM -0200, Marcelo Ricardo Leitner wrote:
>>> That will catch possible miscalculations too, I don't like we're
>>> polluting this with many WARN_ONCE, but I don't see any better way to
>>> catch this size miscalculation bugs, so ahead add it.
>>>
>>> BTW, we should also signal the userspace when we fail to build the
>>> message via:
>>>
>>> nfnetlink_set_err(net, 0, group, -ENOBUFS);
>>>
>>> so it knows that we're losing log messages for whatever reason.
>>> Basically, userspace hits -ENOBUFS when calling recv(), which means
>>> netlink is losing messages. I don't think we really need the
>>> statistics.
>>
>> Cool. Then we probably don't need the WARN_ON unless we really want
>> those numbers, or even so. As we will be calling nfnetlink_set_err,
>> we have other ways of debugging. Wouldn't be as ready as a WARN_ONCE
>> in there, yes.. but a systemtap script can easily get a hold in
>> there.
>>
>> So no WARN_ONCE, just the nfnetlink_set_err() call? Like this?
>
> The ENOBUFS notice won't be enough. This can be triggered if the rate
> of log message is too high, or the userspace process is too slow to
> empty the socket queue.
>
> I think we need both WARN_ONCE (tells us that miscalculation is
> happening, ie. we have a bug) and the nfnetlink_set_err (tells
> userspace it's losing log messages, so logging becomes
> unreliable/approximative).

yeah.. okay, will put it in too.

Thanks,
Marcelo