netdev - Re: [patch net-next 6/8] ipv4: fib: Add an API to request a FIB dump

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Message-ID: <e795e6e0-a680-a2c3-7d5e-afd966104a4a@stressinduktion.org>
Date:   Wed, 16 Nov 2016 15:51:01 +0100
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, idosch@...lanox.com, eladr@...lanox.com,
        yotamg@...lanox.com, nogahf@...lanox.com, arkadis@...lanox.com,
        ogerlitz@...lanox.com, roopa@...ulusnetworks.com,
        dsa@...ulusnetworks.com, nikolay@...ulusnetworks.com,
        andy@...yhouse.net, vivien.didelot@...oirfairelinux.com,
        andrew@...n.ch, f.fainelli@...il.com, alexander.h.duyck@...el.com,
        kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
        kaber@...sh.net
Subject: Re: [patch net-next 6/8] ipv4: fib: Add an API to request a FIB dump

On 16.11.2016 15:09, Jiri Pirko wrote:
> From: Ido Schimmel <idosch@...lanox.com>
> 
> Commit b90eb7549499 ("fib: introduce FIB notification infrastructure")
> introduced a new notification chain to notify listeners (f.e., switchdev
> drivers) about addition and deletion of routes.
> 
> However, upon registration to the chain the FIB tables can already be
> populated, which means potential listeners will have an incomplete view
> of the tables.
> 
> Solve that by adding an API to request a FIB dump. The dump itself it
> done using RCU in order not to starve consumers that need RTNL to make
> progress.
> 
> Signed-off-by: Ido Schimmel <idosch@...lanox.com>
> Signed-off-by: Jiri Pirko <jiri@...lanox.com>

Have you looked at potential inconsistencies resulting of RCU walking
the table and having concurrent inserts?

I don't see a way around doing a journal like in filesystems somehow,
but maybe the effects are not that severe and it is not a problem after all.

Bye,
Hannes