netdev - Re: [iproute PATCH] libnetlink: Double the dump buffer size

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Date:	Sat, 05 Mar 2016 22:12:16 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Stephen Hemminger <shemming@...cade.com>, Phil Sutter <phil@....cc>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [iproute PATCH] libnetlink: Double the dump buffer size

On Fri, 2016-03-04 at 15:35 -0800, Stephen Hemminger wrote:
> 
> > There have been reports about 'ip addr' printing "Message
> > truncated" on
[...]
> I thought this was addressed in kernel by making the VF info
> optional.
> The netlink protocol is showing some strain, this is one of them.

I don't know how the dump is split here, but we had a similar issue
with nl80211 - originally each physical device info had to fit into a
single message (one message during dump for each device), but we fixed
that by having userspace to set a flag when it's able to understand a
multi-message single physical device info.

Before:
 msg1: phy1: A, B, C
 msg2: phy2: A, B, C

After:
 msg1: phy1: A
 msg2: phy1: B
 msg3: phy1: C
 msg4: phy1: D
 msg5: phy2: A
 [...]

For userspace not setting the flag, it only get partial info today for
compatibility (A, B, C, not D), but in our particular case this was
perfectly reasonable since it would be unaware of the new capabilities
anyway.

I don't know precisely enough what the issue at hand is to comment
whether such an approach will be feasible here, but it seems it could
be.

johannes