[Devel] Re: [PATCH 1/12] L2 network namespace: current network namespace operations

[Eric W. Biederman]

Dmitry Mishin <dim at openvz.org> writes:

> On Thursday 07 December 2006 12:37, Cedric Le Goater wrote:
>> Dmitry Mishin wrote:
>> > Added functions and macros required to operate with current network
> namespaces.
>> > They are required in order to switch network namespace for incoming packets
> and
>> > to not extend current network interface by addtiotional network namespace
> argue.
>> > 
>> > Signed-off-by: Dmitry Mishin <dim at openvz.org>
>> > 
>> > ---
>> > include/linux/net_namespace.h | 41 +++++++++++++++++++++++++++++++++++++++--
>> >  kernel/nsproxy.c              |    1 +
>> >  net/core/net_namespace.c      |    2 ++
>> >  3 files changed, 42 insertions(+), 2 deletions(-)
>> > 
>> > --- linux-2.6.19-rc6-mm2.orig/include/linux/net_namespace.h
>> > +++ linux-2.6.19-rc6-mm2/include/linux/net_namespace.h
>> > @@ -7,6 +7,7 @@
>> >  
>> >  struct net_namespace {
>> >  	struct kref	kref;
>> > +	struct nsproxy	*ns;
>> >  };
>> >
>> 
>> why do you need that back pointer ? 
>> 
>> ( The answer must be in the following patches but I'm being lazy and 
>>   asking the author :)
> Because for the incoming packets, I need to switch networking namespace
> per-task and not per-nsproxy. If I switch it just in current->nsproxy, it means
> that all tasks shring this nsproxy will switch network context.
>
> It is one of the reasons, why we need per-task exec_context pointer.

Ugh.

If necessary push_net_ns and pop_net_ns should be implemented like get_fs
and set_fs.  Using a sane variable in thread_info, or per cpu.

I'm not at all certain I'm comfortable doing this in interrupt context.

Assuming we are doing it then we should do it for every path both socket
and network device and do the lookup once and the cache it globally in
the current execution context.

We should not change current->nsproxy.   I don't think for packet processing
we need to change every namespace do we?  The uid namespace and the like should
be irrelevant correct?

Eric
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