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

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Message-ID: <20150121115924.GW3012@acer.localdomain>
Date:	Wed, 21 Jan 2015 11:59:25 +0000
From:	Patrick McHardy <kaber@...sh.net>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>, 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 21.01, Thomas Graf wrote:
> On 01/21/15 at 10:40am, Patrick McHardy wrote:
> > On the danger of repeating myself, every (converted) user requires
> > that we at least keep the existing semantics since it is exposed to
> > userspace. My opinion is that NLM_F_DUMP_INTR is fine if userspace
> > indicates support, but without that, we have to take care of that
> > in the kernel.
> 
> Absolutely agreed. I think this is an excellent low cost path for
> future users where dumps are rare.
> 
> > An automatic restart handles this well. Userspace always had to
> > expect duplicates.
> 
> Maybe I don't understand the restart yet. How do you restart if the
> dump was already started and the user has read part of the dump?

You use the mutex to prevent concurrent resizes and dumps, for dumps
that have left the kernel you simply reset the iterator state after
a resize operation.
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