netdev - Re: [PATCH 1/3] netlink: fix NETLINK_RECV_NO_ENOBUFS in netlink_set

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Date:	Thu, 18 Mar 2010 18:01:54 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Patrick McHardy <kaber@...sh.net>
CC:	netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH 1/3] netlink: fix NETLINK_RECV_NO_ENOBUFS in netlink_set_err()

Patrick McHardy wrote:
> Pablo Neira Ayuso wrote:
>> Patrick McHardy wrote:
>>> Pablo Neira Ayuso wrote:
>>>> Yes, allocation is a different situation but we still report ENOBUFS to
>>>> user-space. I think that NETLINK_RECV_NO_ENOBUFS is there to a) disable
>>>> ENOBUFS reports to user-space and b) disable Netlink congestion.
>>>>
>>>>> Is there any problem with these errors?
>>>> Specifically in ctnetlink, if we fail to allocate a message in ctnetlink
>>>> and NETLINK_RECV_NO_ENOBUFS is set, we still lose an event and that
>>>> should not happen.
>>> I assume you mean "not set"? Otherwise I fail to follow :)
>> OK, I'll try again :-)
>>
>> Currently, no matter if NETLINK_RECV_NO_ENOBUFS is set or not: if we
>> fail to allocate the netlink message, then ctnetlink_conntrack_event()
>> returns 0. Thus, we report ENOBUFS to user-space and we lose the event.
>>
>> With my patches, if NETLINK_RECV_NO_ENOBUFS is set and we fail to
>> allocate the message, we don't report ENOBUFS and we don't lose the event.
> 
> That last part is what keeps confusing me. With your patch, if the
> ENOBUFS options is set, we don't report the error to userspace
> and therefore don't return it to conntrack, thus we *do* loose the
> event. Which is correct however.

Sorry, I'm being a bit imprecise myself: we do lose the event anyway.
However, with my patch, if the NO_ENOBUFS option is set, we keep the
event in the ctevent cache, so we can try to deliver it again with the
next packet (this is what I initially meant with "we don't lose the
event", yes, confusing...).

> Did I get it right this time? :)

I think so! :-)
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