Subject: Re: [PATCH 3/4] SUNRPC: service destruction in network namespace context

From: Stanislav Kinsbursky <[email-masked]>
Date: Fri, 27 Jan 2012 13:08:06 +0400

27.01.2012 01:14, J. Bruce Fields пишет:
> On Wed, Jan 25, 2012 at 05:47:26PM +0400, Stanislav Kinsbursky wrote:
>> This patch introduces network namespace filter for service destruction
>> function.
>> Nothing special here - just do exactly the same operations, but only for
>> tranports in passed networks namespace context.
>> BTW, BUG_ON() checks for empty service transports lists were returned into
>> svc_destroy() function. This is because of swithing generic svc_close_all() to
>> networks namespace dependable svc_close_net().
>>
>> Signed-off-by: Stanislav Kinsbursky<[email-masked]>
>>
>> ---
>>   include/linux/sunrpc/svcsock.h |    2 +-
>>   net/sunrpc/svc.c               |    9 +++++++--
>>   net/sunrpc/svc_xprt.c          |   27 +++++++++++++++++----------
>>   3 files changed, 25 insertions(+), 13 deletions(-)
>>
>> diff --git a/include/linux/sunrpc/svcsock.h b/include/linux/sunrpc/svcsock.h
>> index c84e974..cb4ac69 100644
>> --- a/include/linux/sunrpc/svcsock.h
>> +++ b/include/linux/sunrpc/svcsock.h
>> @@ -34,7 +34,7 @@ struct svc_sock {
>>   /*
>>    * Function prototypes.
>>    */
>> -void		svc_close_all(struct svc_serv *);
>> +void		svc_close_net(struct svc_serv *, struct net *);
>>   int		svc_recv(struct svc_rqst *, long);
>>   int		svc_send(struct svc_rqst *);
>>   void		svc_drop(struct svc_rqst *);
>> diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
>> index a8b49a0..279bbd8 100644
>> --- a/net/sunrpc/svc.c
>> +++ b/net/sunrpc/svc.c
>> @@ -517,6 +517,8 @@ EXPORT_SYMBOL_GPL(svc_create_pooled);
>>   void
>>   svc_destroy(struct svc_serv *serv)
>>   {
>> +	struct net *net = current->nsproxy->net_ns;
>> +
>>   	dprintk("svc: svc_destroy(%s, %d)\n",
>>   				serv->sv_program->pg_name,
>>   				serv->sv_nrthreads);
>> @@ -539,10 +541,13 @@ svc_destroy(struct svc_serv *serv)
>>   	 * caller is using--nfsd_mutex in the case of nfsd).  So it's
>>   	 * safe to traverse those lists and shut everything down:
>>   	 */
>> -	svc_close_all(serv);
>> +	svc_close_net(serv, net);
>> +
>> +	BUG_ON(!list_empty(&serv->sv_permsocks));
>> +	BUG_ON(!list_empty(&serv->sv_tempsocks));
>
> I'm confused--what guarantees this is true, at this point?
>

Hi, Bruce.
I'm confused with your question. IOW, this must be true, because this code is 
executed only in case of last service thread is exiting, doesn't it?

> There are two ways I could imagine containerizing svc_serv: either we
> create a new one for each namespace, or we share a single global one
> between them.
>

This is done for the second one.

> If the former, then something that takes a "serv" argument shouldn't
> also need a "net" argument--the serv should already know which namespace
> it belongs to.
>
> If the latter, then these lists could have sockets from multiple
> namespaces, and they aren't guaranteed to be empty here.
>
> ?
>

I'll explain it on Lockd example (this code is done already - I just haven't 
sent it yet).
Lockd is still only one thread and can handle lock requests from different 
network namespaces:
1) Introduced per-net lockd users counter and resources.
2) nlmsvc_users counter become global one. I.e. it's equal to sum of all per-net 
lockd users counters.
3) For each lockd_up() call global and current net lockd users counters are 
increased by one.
3) On lockd_up() call: if nlmsvc_users if equal to 0, then lockd thread is started.
4) On lockd_up() call: if current network context lockd users counter equal to 
0, then resources for Lockd service are allocated in current network context.
5) On lockd_down() call: if current network context lockd users counter equal to 
0, then resources for Lockd service are released in current network context 
(svc_shutdown_net() introduced in this series).
6) On lockd_down() call: if nlmsvc_users if equal to 0, then lockd thread is 
stopped and svc_destroy is called. And herewe can expect, that no service 
transports left.

I've just realized, that probably it's possible to implement some more generic 
helpers in SUNRPC code to make the code looks clearer.
I would appreciate for any advices how to do so.

-- 
Best regards,
Stanislav Kinsbursky