Re: [pnfs] [RFC 61/85] nfs41: Add backchannel processing support to RPC state machine

[Benny Halevy <bhalevy@panasas.com>]

On Nov. 10, 2008, 22:29 +0200, Benny Halevy <bhalevy@panasas.com> wrote:
> Adds rpc_run_bc_task() which is called by the NFS callback service to
> process backchannel requests.  It performs similar work to rpc_run_task()
> though "schedules" the backchannel task to be executed starting at the
> call_trasmit state in the RPC state machine.
> 
> It also introduces some miscellaneous updates to the argument validation,
> call_transmit, and transport cleanup functions to take into account
> that there are now forechannel and backchannel tasks.
> 
> Backchannel requests do not carry an RPC message structure, since the
> payload has already been XDR encoded using the existing NFSv4 callback
> mechanism.
> 
> Signed-off-by: Ricardo Labiaga <ricardo.labiaga@netapp.com>
> Signed-off-by: Benny Halevy <bhalevy@panasas.com>
> ---
>  include/linux/sunrpc/sched.h |    2 +
>  include/linux/sunrpc/xprt.h  |   12 +++++++++
>  net/sunrpc/clnt.c            |   52 ++++++++++++++++++++++++++++++++++++++++-
>  net/sunrpc/stats.c           |    6 +++-
>  net/sunrpc/sunrpc.h          |   35 ++++++++++++++++++++++++++++
>  net/sunrpc/xprt.c            |   36 ++++++++++++++++++++++++-----
>  6 files changed, 133 insertions(+), 10 deletions(-)
>  create mode 100644 net/sunrpc/sunrpc.h
> 
> diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h
> index 1773768..4010977 100644
> --- a/include/linux/sunrpc/sched.h
> +++ b/include/linux/sunrpc/sched.h
> @@ -210,6 +210,8 @@ struct rpc_wait_queue {
>   */
>  struct rpc_task *rpc_new_task(const struct rpc_task_setup *);
>  struct rpc_task *rpc_run_task(const struct rpc_task_setup *);
> +struct rpc_task *rpc_run_bc_task(struct rpc_rqst *req,
> +				const struct rpc_call_ops *ops);
>  void		rpc_put_task(struct rpc_task *);
>  void		rpc_exit_task(struct rpc_task *);
>  void		rpc_release_calldata(const struct rpc_call_ops *, void *);
> diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
> index 035431b..45a92e2 100644
> --- a/include/linux/sunrpc/xprt.h
> +++ b/include/linux/sunrpc/xprt.h
> @@ -215,6 +215,18 @@ struct rpc_xprt {
>  						/* buffer in use */
>  #endif /* CONFIG_NFS_V4_1 */
>  
> +#if defined(CONFIG_NFS_V4_1)
> +static inline int bc_prealloc(struct rpc_rqst *req)
> +{
> +	return test_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
> +}
> +#else
> +static inline int bc_prealloc(struct rpc_rqst *req)
> +{
> +	return 0;
> +}
> +#endif /* CONFIG_NFS_V4_1 */
> +
>  struct xprt_create {
>  	int			ident;		/* XPRT_TRANSPORT identifier */
>  	struct sockaddr *	srcaddr;	/* optional local address */
> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
> index dd0ff2d..f5418ac 100644
> --- a/net/sunrpc/clnt.c
> +++ b/net/sunrpc/clnt.c
> @@ -36,7 +36,9 @@
>  #include <linux/sunrpc/clnt.h>
>  #include <linux/sunrpc/rpc_pipe_fs.h>
>  #include <linux/sunrpc/metrics.h>
> +#include <linux/sunrpc/bc_xprt.h>
>  
> +#include "sunrpc.h"
>  
>  #ifdef RPC_DEBUG
>  # define RPCDBG_FACILITY	RPCDBG_CALL
> @@ -602,6 +604,51 @@ rpc_call_async(struct rpc_clnt *clnt, const struct rpc_message *msg, int flags,
>  }
>  EXPORT_SYMBOL_GPL(rpc_call_async);
>  
> +#if defined(CONFIG_NFS_V4_1)
> +/**
> + * rpc_run_bc_task - Allocate a new RPC task for backchannel use, then run
> + * rpc_execute against it
> + * @ops: RPC call ops
> + */
> +struct rpc_task *rpc_run_bc_task(struct rpc_rqst *req,
> +					const struct rpc_call_ops *tk_ops)
> +{
> +	struct rpc_task *task;
> +	struct xdr_buf *xbufp = &req->rq_snd_buf;
> +	struct rpc_task_setup task_setup_data = {
> +		.callback_ops = tk_ops,
> +	};
> +
> +	dprintk("RPC: rpc_run_bc_task req= %p\n", req);
> +	/*
> +	 * Create an rpc_task to send the data
> +	 */
> +	task = rpc_new_task(&task_setup_data);

review 11-14: we can't do that.
Trond suggests to factor out what we need in call_transmit
i.e. never call call_status. (only error we need to handle is -EAGAIN

setting up a task for that is the easiest way to go.
we should be able to reuse the existing marshalled stuff that the svc
prepared rather than copying the data.

> +	if (!task) {
> +		xprt_free_bc_request(req);
> +		goto out;
> +	}
> +	task->tk_rqstp = req;
> +
> +	/*
> +	 * Set up the xdr_buf length.
> +	 * This also indicates that the buffer is XDR encoded already.
> +	 */
> +	xbufp->len = xbufp->head[0].iov_len + xbufp->page_len +
> +			xbufp->tail[0].iov_len;
> +
> +	task->tk_action = call_transmit;
> +	atomic_inc(&task->tk_count);
> +	BUG_ON(atomic_read(&task->tk_count) != 2);
> +	rpc_execute(task);
> +
> +out:
> +	dprintk("RPC: rpc_run_bc_task: task= %p\n", task);
> +	return task;
> +}
> +EXPORT_SYMBOL_GPL(rpc_run_bc_task);
> +#endif /* CONFIG_NFS_V4_1 */
> +
>  void
>  rpc_call_start(struct rpc_task *task)
>  {
> @@ -1094,10 +1141,11 @@ call_transmit(struct rpc_task *task)
>  	 * in order to allow access to the socket to other RPC requests.
>  	 */
>  	call_transmit_status(task);
> -	if (task->tk_msg.rpc_proc->p_decode != NULL)
> +	if (rpc_reply_expected(task))
>  		return;
>  	task->tk_action = rpc_exit_task;
> -	rpc_wake_up_queued_task(&task->tk_xprt->pending, task);
> +	if (task->tk_client != NULL)
> +		rpc_wake_up_queued_task(&task->tk_xprt->pending, task);
>  }
>  
>  /*
> diff --git a/net/sunrpc/stats.c b/net/sunrpc/stats.c
> index 50b049c..89dc28e 100644
> --- a/net/sunrpc/stats.c
> +++ b/net/sunrpc/stats.c
> @@ -141,12 +141,14 @@ EXPORT_SYMBOL_GPL(rpc_free_iostats);
>  void rpc_count_iostats(struct rpc_task *task)
>  {
>  	struct rpc_rqst *req = task->tk_rqstp;
> -	struct rpc_iostats *stats = task->tk_client->cl_metrics;
> +	struct rpc_iostats *stats;
>  	struct rpc_iostats *op_metrics;
>  	long rtt, execute, queue;
>  
> -	if (!stats || !req)
> +	if (!task->tk_client || task->tk_client->cl_metrics || !req)
>  		return;
> +
> +	stats = task->tk_client->cl_metrics;
>  	op_metrics = &stats[task->tk_msg.rpc_proc->p_statidx];
>  
>  	op_metrics->om_ops++;
> diff --git a/net/sunrpc/sunrpc.h b/net/sunrpc/sunrpc.h
> new file mode 100644
> index 0000000..b462de4
> --- /dev/null
> +++ b/net/sunrpc/sunrpc.h
> @@ -0,0 +1,35 @@
> +/******************************************************************************
> +
> +(c) 2008 Network Appliance, Inc.  All Rights Reserved.
> +
> +Network Appliance provides this source code under the GPL v2 License.
> +The GPL v2 license is available at
> +http://opensource.org/licenses/gpl-license.php.
> +
> +THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
> +"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
> +LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
> +A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
> +CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
> +EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
> +PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
> +PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
> +LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
> +NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
> +SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> +
> +******************************************************************************/
> +
> +/*
> + * Functions and macros used internally by RPC
> + */
> +
> +#ifndef _NET_SUNRPC_SUNRPC_H
> +#define _NET_SUNRPC_SUNRPC_H
> +
> +#define rpc_reply_expected(task) \
> +	(((task)->tk_msg.rpc_proc != NULL) && \
> +	((task)->tk_msg.rpc_proc->p_decode != NULL))
> +
> +#endif /* _NET_SUNRPC_SUNRPC_H */
> +
> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> index 848a7af..cc1e5f2 100644
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -12,8 +12,9 @@
>   *  -	Next, the caller puts together the RPC message, stuffs it into
>   *	the request struct, and calls xprt_transmit().
>   *  -	xprt_transmit sends the message and installs the caller on the
> - *	transport's wait list. At the same time, it installs a timer that
> - *	is run after the packet's timeout has expired.
> + *	transport's wait list. At the same time, if a reply is expected,
> + *	it installs a timer that is run after the packet's timeout has
> + *	expired.
>   *  -	When a packet arrives, the data_ready handler walks the list of
>   *	pending requests for that transport. If a matching XID is found, the
>   *	caller is woken up, and the timer removed.
> @@ -46,6 +47,8 @@
>  #include <linux/sunrpc/clnt.h>
>  #include <linux/sunrpc/metrics.h>
>  
> +#include "sunrpc.h"
> +
>  /*
>   * Local variables
>   */
> @@ -852,7 +855,10 @@ void xprt_transmit(struct rpc_task *task)
>  	dprintk("RPC: %5u xprt_transmit(%u)\n", task->tk_pid, req->rq_slen);
>  
>  	if (!req->rq_received) {
> -		if (list_empty(&req->rq_list)) {
> +		if (list_empty(&req->rq_list) && rpc_reply_expected(task)) {
> +			/*
> +			 * Add to the list only if we're expecting a reply
> +			 */
>  			spin_lock_bh(&xprt->transport_lock);
>  			/* Update the softirq receive buffer */
>  			memcpy(&req->rq_private_buf, &req->rq_rcv_buf,
> @@ -883,8 +889,13 @@ void xprt_transmit(struct rpc_task *task)
>  		/* Don't race with disconnect */
>  		if (!xprt_connected(xprt))
>  			task->tk_status = -ENOTCONN;
> -		else if (!req->rq_received)
> +		else if (!req->rq_received && rpc_reply_expected(task)) {
> +			/*
> +			 * Sleep on the pending queue since
> +			 * we're expecting a reply.
> +			 */
>  			rpc_sleep_on(&xprt->pending, task, xprt_timer);
> +		}
>  		spin_unlock_bh(&xprt->transport_lock);
>  		return;
>  	}
> @@ -967,11 +978,15 @@ static void xprt_request_init(struct rpc_task *task, struct rpc_xprt *xprt)
>   */
>  void xprt_release(struct rpc_task *task)
>  {
> -	struct rpc_xprt	*xprt = task->tk_xprt;
> +	struct rpc_xprt	*xprt;
>  	struct rpc_rqst	*req;
> +	int prealloc;
>  
> +	BUG_ON(atomic_read(&task->tk_count) < 0);
>  	if (!(req = task->tk_rqstp))
>  		return;
> +	prealloc = bc_prealloc(req);	/* Preallocated backchannel request? */
> +	xprt = req->rq_xprt;
>  	rpc_count_iostats(task);
>  	spin_lock_bh(&xprt->transport_lock);
>  	xprt->ops->release_xprt(xprt, task);
> @@ -984,10 +999,19 @@ void xprt_release(struct rpc_task *task)
>  		mod_timer(&xprt->timer,
>  				xprt->last_used + xprt->idle_timeout);
>  	spin_unlock_bh(&xprt->transport_lock);
> -	xprt->ops->buf_free(req->rq_buffer);
> +	if (!bc_prealloc(req))
> +		xprt->ops->buf_free(req->rq_buffer);
>  	task->tk_rqstp = NULL;
>  	if (req->rq_release_snd_buf)
>  		req->rq_release_snd_buf(req);
> +
> +	/*
> +	 * Early exit if this is a backchannel preallocated request.
> +	 * There is no need to have it added to the RPC slot list.
> +	 */
> +	if (prealloc)
> +		return;
> +
>  	memset(req, 0, sizeof(*req));	/* mark unused */
>  
>  	dprintk("RPC: %5u release request %p\n", task->tk_pid, req);