Re: [PATCH] nfsd: use nfs client rpc callback program

[Benny Halevy <bhalevy@panasas.com>]

On Sep. 17, 2008, 18:10 -0500, "J. Bruce Fields" <bfields@fieldses.org> wrote:
> On Wed, Sep 17, 2008 at 02:43:44PM -0500, Benny Halevy wrote:
>> From: Benny Halevy <bhalevy@panasas.com>
>>
>> since commit ff7d9756b501744540be65e172d27ee321d86103
>> "nfsd: use static memory for callback program and stats"
>> do_probe_callback uses a static callback program
>> (NFS4_CALLBACK) rather than the one set in clp->cl_callback.cb_prog
>> as passed in by the client in setclientid (4.0)
>> or create_session (4.1).
> 
> Ugh, yes, sorry about that.  (I wonder why pynfs testing didn't catch
> this?  Oh, I guess it's because NFS4_CALLBACK is the program number our
> client always gives us.)

Well, Fred (thanks!) added a test today which uses a non-default
callback program and he sees a corresponding callback coming back.

(Note that this test is not absolutely generic as the server is
not required to probe the callback immediately, or at all, after
setclientid or create_session.)

> 
>> @@ -371,6 +356,8 @@ static int do_probe_callback(void *data)
>>  		.to_maxval	= (NFSD_LEASE_TIME/2) * HZ,
>>  		.to_exponential	= 1,
>>  	};
>> +	static struct rpc_stat	cb_stats;
>> +	struct rpc_program	cb_program;
>>  	struct rpc_create_args args = {
>>  		.protocol	= IPPROTO_TCP,
>>  		.address	= (struct sockaddr *)&addr,
>> @@ -394,6 +381,20 @@ static int do_probe_callback(void *data)
>>  	addr.sin_port = htons(cb->cb_port);
>>  	addr.sin_addr.s_addr = htonl(cb->cb_addr);
>>  
>> +	/* Initialize rpc_program */
>> +	memset(&cb_program, 0, sizeof(cb_program));
>> +	cb_program.name = "nfs4_cb";
>> +	cb_program.number = clp->cl_callback.cb_prog;
>> +	cb_program.nrvers = ARRAY_SIZE(nfs_cb_version);
>> +	cb_program.version = nfs_cb_version;
>> +	cb_program.stats = &cb_stats;
>> +	memset(&cb_stats, 0, sizeof(cb_stats));
>> +	cb_stats.program = &cb_program;
> 
> You don't want a pointer to data on the stack here, do you?

Hmm, you're right...
I went back and forth whether this should be allocated statically,
dynamically, or on the stack.  I was mislead by the fact we're doing
a sync rpc call, but indeed this needs to live until the nfs client
is destroyed.  I'm trying to fully understand what Olga saw
before coming up with a new proposal... maybe putting the cb_program
back into struct nfs4_callback and just make cb_stats static would
provide a solution of the problem Olga witnessed and keep everybody
happy.

Benny

> 
> --b.