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

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Date:	Thu, 18 Mar 2010 17:34:26 +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:
>>>> Currently, ENOBUFS errors are reported to the socket via
>>>> netlink_set_err() even if NETLINK_RECV_NO_ENOBUFS is set. However,
>>>> that should not happen. This fixes this problem and it changes the
>>>> prototype of netlink_set_err() to return the number of sockets whose
>>>> error has been set. This allows to know if any error has been set.
>>>> This return value is used in the next patch in these bugfix series.
>>> But that only happens if we have a message allocate error, which is
>>> a different situation than rcvqueue overrun, which I thought the
>>> original patch was supposed to handle (disable netlink congestion
>>> control).
>> 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.
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