netdev - Re: [PATCH 3/3] netlink: Lock out table resizes while dumping Netlink sockets

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Message-ID: <20150121103421.GR20315@casper.infradead.org>
Date:	Wed, 21 Jan 2015 10:34:21 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Patrick McHardy <kaber@...sh.net>, davem@...emloft.net,
	paulmck@...ux.vnet.ibm.com, ying.xue@...driver.com,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: [PATCH 3/3] netlink: Lock out table resizes while dumping
 Netlink sockets

On 01/21/15 at 08:58pm, Herbert Xu wrote:
> On Wed, Jan 21, 2015 at 09:49:28AM +0000, Thomas Graf wrote:
> >
> > An entry can move between different tables and thus chains need to be
> > marked to identify what list a lookup ended up searching in. It's not
> > the nulls marker itself that is needed, it's the bits in the last next
> > pointer identifying the list that the nulls marker allows to be used
> > which are essential.
> 
> Can you describe in more detail how it's going to be used? I don't
> see how I could use the bit if you need it to indicate the end of
> the list.

Another thought: Instead of storing that bit in the next pointer, we
could require the user to store this bit, i.e. two new function
pointers to rhashtable_params, set_walk_bit() and get_walk_bit(),
which take the hashed object as argument and if a rhashtable user
requires consistent dumps he can provide these functions to store
the flag.
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