netdev - Re: [patch v2 04/11] nf_conntrack_netlink: pass nf_conntrack_netlink module to netlink_dump

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Message-ID: <20120926095837.GA23815@1984>
Date:	Wed, 26 Sep 2012 11:58:37 +0200
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Gao feng <gaofeng@...fujitsu.com>
Cc:	davem@...emloft.net, eric.dumazet@...il.com,
	steffen.klassert@...unet.com, netfilter-devel@...r.kernel.org,
	linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
	linux-crypto@...r.kernel.org, stephen.hemminger@...tta.com,
	jengelh@...i.de
Subject: Re: [patch v2 04/11] nf_conntrack_netlink: pass
 nf_conntrack_netlink module to netlink_dump_start

On Wed, Sep 26, 2012 at 05:42:31PM +0800, Gao feng wrote:
> Hi Pablo:
> 
> 于 2012年09月26日 17:26, Pablo Neira Ayuso 写道:
> > On Wed, Sep 26, 2012 at 04:41:21PM +0800, Gao feng wrote:
> >> use proper netlink_dump_control.done and .module to avoid panic.
> >>
> >> Signed-off-by: Gao feng <gaofeng@...fujitsu.com>
> >> ---
> >>  net/netfilter/nf_conntrack_netlink.c |    8 ++++++++
> >>  1 files changed, 8 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
> >> index 9807f32..509a257 100644
> >> --- a/net/netfilter/nf_conntrack_netlink.c
> >> +++ b/net/netfilter/nf_conntrack_netlink.c
> >> @@ -706,6 +706,7 @@ static int ctnetlink_done(struct netlink_callback *cb)
> >>  		nf_ct_put((struct nf_conn *)cb->args[1]);
> >>  	if (cb->data)
> >>  		kfree(cb->data);
> >> +	netlink_dump_done(cb);
> > 
> > I think you can call netlink_dump_done from af_netlink.c:
> > 
> > static int netlink_dump(struct sock *sk) 
> >         ...
> >         if (cb->done) {
> >                 cb->done(cb);
> >                 netlink_dump_done(...);
> >         }
> > 
> > Thus, you don't need to change netlink_dump_control in every netlink
> > subsystem.
> 
> because cb->done is called by netlink_sock_destruct too,it's very usefully
> when userspace program only send dump request to kernel without reading
> data from kernel.

Then add that to netlink_sock_destruct as well. If possible, I prefer
if this remains in the netlink core to avoid leaking module refcount
if you forget to call netlink_dump_done.

> > 
> >>  	return 0;
> >>  }
> >>  
> >> @@ -1022,6 +1023,7 @@ ctnetlink_get_conntrack(struct sock *ctnl, struct sk_buff *skb,
> >>  		struct netlink_dump_control c = {
> >>  			.dump = ctnetlink_dump_table,
> >>  			.done = ctnetlink_done,
> >> +			.module = THIS_MODULE,
> > 
> > You can do something similar to:
> > 
> > 9f00d97 netlink: hide struct module parameter in netlink_kernel_create
> > 
> > by definiting netlink_dump_start as static inline and using
> > THIS_MODULE from there.
> > 
> > If I'm not missing anything, with those two changes, you will not need
> > to modify any caller and it will result one single patch.
> > 
> 
> You can see the patch [11/11], THIS_MODULE in infiniband/core/cma.c
> means module rdma_cm,but we call netlink_dump_start in infiniband/core/netlink.c

You can still use __netlink_dump_start for that case, which allows you
to specify a custom struct module * parameter. But for most cases,
netlink_dump_start (which hides THIS_MODULE) should be fine.

> we should make sure the cb.moudle point to the module which cb.dump belongs to.
> we can call netlink_dump_start to set cb->dump everywhere, so I think we still
> need to pass struct module to the netlink_callback.
> 
> thanks for your comments!
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