xprt.c

linux 内核源代码

/*
 *  linux/net/sunrpc/xprt.c
 *
 *  This is a generic RPC call interface supporting congestion avoidance,
 *  and asynchronous calls.
 *
 *  The interface works like this:
 *
 *  -	When a process places a call, it allocates a request slot if
 *	one is available. Otherwise, it sleeps on the backlog queue
 *	(xprt_reserve).
 *  -	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.
 *  -	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.
 *  -	When no reply arrives within the timeout interval, the timer is
 *	fired by the kernel and runs xprt_timer(). It either adjusts the
 *	timeout values (minor timeout) or wakes up the caller with a status
 *	of -ETIMEDOUT.
 *  -	When the caller receives a notification from RPC that a reply arrived,
 *	it should release the RPC slot, and process the reply.
 *	If the call timed out, it may choose to retry the operation by
 *	adjusting the initial timeout value, and simply calling rpc_call
 *	again.
 *
 *  Support for async RPC is done through a set of RPC-specific scheduling
 *  primitives that `transparently' work for processes as well as async
 *  tasks that rely on callbacks.
 *
 *  Copyright (C) 1995-1997, Olaf Kirch <[e-mail]>
 *
 *  Transport switch API copyright (C) 2005, Chuck Lever <[e-mail]>
 */

#include <linux/module.h>

#include <linux/types.h>
#include <linux/interrupt.h>
#include <linux/workqueue.h>
#include <linux/net.h>

#include <linux/sunrpc/clnt.h>
#include <linux/sunrpc/metrics.h>

/*
 * Local variables
 */

#ifdef RPC_DEBUG
# define RPCDBG_FACILITY	RPCDBG_XPRT
#endif

/*
 * Local functions
 */
static void	xprt_request_init(struct rpc_task *, struct rpc_xprt *);
static inline void	do_xprt_reserve(struct rpc_task *);
static void	xprt_connect_status(struct rpc_task *task);
static int      __xprt_get_cong(struct rpc_xprt *, struct rpc_task *);

static DEFINE_SPINLOCK(xprt_list_lock);
static LIST_HEAD(xprt_list);

/*
 * The transport code maintains an estimate on the maximum number of out-
 * standing RPC requests, using a smoothed version of the congestion
 * avoidance implemented in 44BSD. This is basically the Van Jacobson
 * congestion algorithm: If a retransmit occurs, the congestion window is
 * halved; otherwise, it is incremented by 1/cwnd when
 *
 *	-	a reply is received and
 *	-	a full number of requests are outstanding and
 *	-	the congestion window hasn't been updated recently.
 */
#define RPC_CWNDSHIFT		(8U)
#define RPC_CWNDSCALE		(1U << RPC_CWNDSHIFT)
#define RPC_INITCWND		RPC_CWNDSCALE
#define RPC_MAXCWND(xprt)	((xprt)->max_reqs << RPC_CWNDSHIFT)

#define RPCXPRT_CONGESTED(xprt) ((xprt)->cong >= (xprt)->cwnd)

/**
 * xprt_register_transport - register a transport implementation
 * @transport: transport to register
 *
 * If a transport implementation is loaded as a kernel module, it can
 * call this interface to make itself known to the RPC client.
 *
 * Returns:
 * 0:		transport successfully registered
 * -EEXIST:	transport already registered
 * -EINVAL:	transport module being unloaded
 */
int xprt_register_transport(struct xprt_class *transport)
{
	struct xprt_class *t;
	int result;

	result = -EEXIST;
	spin_lock(&xprt_list_lock);
	list_for_each_entry(t, &xprt_list, list) {
		/* don't register the same transport class twice */
		if (t->ident == transport->ident)
			goto out;
	}

	result = -EINVAL;
	if (try_module_get(THIS_MODULE)) {
		list_add_tail(&transport->list, &xprt_list);
		printk(KERN_INFO "RPC: Registered %s transport module.\n",
			transport->name);
		result = 0;
	}

out:
	spin_unlock(&xprt_list_lock);
	return result;
}
EXPORT_SYMBOL_GPL(xprt_register_transport);

/**
 * xprt_unregister_transport - unregister a transport implementation
 * transport: transport to unregister
 *
 * Returns:
 * 0:		transport successfully unregistered
 * -ENOENT:	transport never registered
 */
int xprt_unregister_transport(struct xprt_class *transport)
{
	struct xprt_class *t;
	int result;

	result = 0;
	spin_lock(&xprt_list_lock);
	list_for_each_entry(t, &xprt_list, list) {
		if (t == transport) {
			printk(KERN_INFO
				"RPC: Unregistered %s transport module.\n",
				transport->name);
			list_del_init(&transport->list);
			module_put(THIS_MODULE);
			goto out;
		}
	}
	result = -ENOENT;

out:
	spin_unlock(&xprt_list_lock);
	return result;
}
EXPORT_SYMBOL_GPL(xprt_unregister_transport);

/**
 * xprt_reserve_xprt - serialize write access to transports
 * @task: task that is requesting access to the transport
 *
 * This prevents mixing the payload of separate requests, and prevents
 * transport connects from colliding with writes.  No congestion control
 * is provided.
 */
int xprt_reserve_xprt(struct rpc_task *task)
{
	struct rpc_xprt	*xprt = task->tk_xprt;
	struct rpc_rqst *req = task->tk_rqstp;

	if (test_and_set_bit(XPRT_LOCKED, &xprt->state)) {
		if (task == xprt->snd_task)
			return 1;
		if (task == NULL)
			return 0;
		goto out_sleep;
	}
	xprt->snd_task = task;
	if (req) {
		req->rq_bytes_sent = 0;
		req->rq_ntrans++;
	}
	return 1;

out_sleep:
	dprintk("RPC: %5u failed to lock transport %p\n",
			task->tk_pid, xprt);
	task->tk_timeout = 0;
	task->tk_status = -EAGAIN;
	if (req && req->rq_ntrans)
		rpc_sleep_on(&xprt->resend, task, NULL, NULL);
	else
		rpc_sleep_on(&xprt->sending, task, NULL, NULL);
	return 0;
}
EXPORT_SYMBOL_GPL(xprt_reserve_xprt);

static void xprt_clear_locked(struct rpc_xprt *xprt)
{
	xprt->snd_task = NULL;
	if (!test_bit(XPRT_CLOSE_WAIT, &xprt->state) || xprt->shutdown) {
		smp_mb__before_clear_bit();
		clear_bit(XPRT_LOCKED, &xprt->state);
		smp_mb__after_clear_bit();
	} else
		queue_work(rpciod_workqueue, &xprt->task_cleanup);
}

/*
 * xprt_reserve_xprt_cong - serialize write access to transports
 * @task: task that is requesting access to the transport
 *
 * Same as xprt_reserve_xprt, but Van Jacobson congestion control is
 * integrated into the decision of whether a request is allowed to be
 * woken up and given access to the transport.
 */
int xprt_reserve_xprt_cong(struct rpc_task *task)
{
	struct rpc_xprt	*xprt = task->tk_xprt;
	struct rpc_rqst *req = task->tk_rqstp;

	if (test_and_set_bit(XPRT_LOCKED, &xprt->state)) {
		if (task == xprt->snd_task)
			return 1;
		goto out_sleep;
	}
	if (__xprt_get_cong(xprt, task)) {
		xprt->snd_task = task;
		if (req) {
			req->rq_bytes_sent = 0;
			req->rq_ntrans++;
		}
		return 1;
	}
	xprt_clear_locked(xprt);
out_sleep:
	dprintk("RPC: %5u failed to lock transport %p\n", task->tk_pid, xprt);
	task->tk_timeout = 0;
	task->tk_status = -EAGAIN;
	if (req && req->rq_ntrans)
		rpc_sleep_on(&xprt->resend, task, NULL, NULL);
	else
		rpc_sleep_on(&xprt->sending, task, NULL, NULL);
	return 0;
}
EXPORT_SYMBOL_GPL(xprt_reserve_xprt_cong);

static inline int xprt_lock_write(struct rpc_xprt *xprt, struct rpc_task *task)
{
	int retval;

	spin_lock_bh(&xprt->transport_lock);
	retval = xprt->ops->reserve_xprt(task);
	spin_unlock_bh(&xprt->transport_lock);
	return retval;
}

static void __xprt_lock_write_next(struct rpc_xprt *xprt)
{
	struct rpc_task *task;
	struct rpc_rqst *req;

	if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
		return;

	task = rpc_wake_up_next(&xprt->resend);
	if (!task) {
		task = rpc_wake_up_next(&xprt->sending);
		if (!task)
			goto out_unlock;
	}

	req = task->tk_rqstp;
	xprt->snd_task = task;
	if (req) {
		req->rq_bytes_sent = 0;
		req->rq_ntrans++;
	}
	return;

out_unlock:
	xprt_clear_locked(xprt);
}

static void __xprt_lock_write_next_cong(struct rpc_xprt *xprt)
{
	struct rpc_task *task;

	if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
		return;
	if (RPCXPRT_CONGESTED(xprt))
		goto out_unlock;
	task = rpc_wake_up_next(&xprt->resend);
	if (!task) {
		task = rpc_wake_up_next(&xprt->sending);
		if (!task)
			goto out_unlock;
	}
	if (__xprt_get_cong(xprt, task)) {
		struct rpc_rqst *req = task->tk_rqstp;
		xprt->snd_task = task;
		if (req) {
			req->rq_bytes_sent = 0;
			req->rq_ntrans++;
		}
		return;
	}
out_unlock:
	xprt_clear_locked(xprt);
}

/**
 * xprt_release_xprt - allow other requests to use a transport
 * @xprt: transport with other tasks potentially waiting
 * @task: task that is releasing access to the transport
 *
 * Note that "task" can be NULL.  No congestion control is provided.
 */
void xprt_release_xprt(struct rpc_xprt *xprt, struct rpc_task *task)
{
	if (xprt->snd_task == task) {
		xprt_clear_locked(xprt);
		__xprt_lock_write_next(xprt);
	}
}
EXPORT_SYMBOL_GPL(xprt_release_xprt);

/**
 * xprt_release_xprt_cong - allow other requests to use a transport
 * @xprt: transport with other tasks potentially waiting
 * @task: task that is releasing access to the transport
 *
 * Note that "task" can be NULL.  Another task is awoken to use the
 * transport if the transport's congestion window allows it.
 */
void xprt_release_xprt_cong(struct rpc_xprt *xprt, struct rpc_task *task)
{
	if (xprt->snd_task == task) {
		xprt_clear_locked(xprt);
		__xprt_lock_write_next_cong(xprt);
	}
}
EXPORT_SYMBOL_GPL(xprt_release_xprt_cong);

static inline void xprt_release_write(struct rpc_xprt *xprt, struct rpc_task *task)
{
	spin_lock_bh(&xprt->transport_lock);
	xprt->ops->release_xprt(xprt, task);
	spin_unlock_bh(&xprt->transport_lock);
}

/*
 * Van Jacobson congestion avoidance. Check if the congestion window
 * overflowed. Put the task to sleep if this is the case.
 */
static int
__xprt_get_cong(struct rpc_xprt *xprt, struct rpc_task *task)
{
	struct rpc_rqst *req = task->tk_rqstp;

	if (req->rq_cong)
		return 1;
	dprintk("RPC: %5u xprt_cwnd_limited cong = %lu cwnd = %lu\n",
			task->tk_pid, xprt->cong, xprt->cwnd);
	if (RPCXPRT_CONGESTED(xprt))
		return 0;
	req->rq_cong = 1;
	xprt->cong += RPC_CWNDSCALE;
	return 1;
}

/*
 * Adjust the congestion window, and wake up the next task
 * that has been sleeping due to congestion
 */
static void
__xprt_put_cong(struct rpc_xprt *xprt, struct rpc_rqst *req)
{
	if (!req->rq_cong)
		return;
	req->rq_cong = 0;
	xprt->cong -= RPC_CWNDSCALE;
	__xprt_lock_write_next_cong(xprt);
}

/**
 * xprt_release_rqst_cong - housekeeping when request is complete
 * @task: RPC request that recently completed
 *
 * Useful for transports that require congestion control.
 */
void xprt_release_rqst_cong(struct rpc_task *task)
{
	__xprt_put_cong(task->tk_xprt, task->tk_rqstp);
}
EXPORT_SYMBOL_GPL(xprt_release_rqst_cong);

/**
 * xprt_adjust_cwnd - adjust transport congestion window
 * @task: recently completed RPC request used to adjust window
 * @result: result code of completed RPC request
 *
 * We use a time-smoothed congestion estimator to avoid heavy oscillation.
 */
void xprt_adjust_cwnd(struct rpc_task *task, int result)
{
	struct rpc_rqst *req = task->tk_rqstp;
	struct rpc_xprt *xprt = task->tk_xprt;
	unsigned long cwnd = xprt->cwnd;

	if (result >= 0 && cwnd <= xprt->cong) {
		/* The (cwnd >> 1) term makes sure
		 * the result gets rounded properly. */
		cwnd += (RPC_CWNDSCALE * RPC_CWNDSCALE + (cwnd >> 1)) / cwnd;
		if (cwnd > RPC_MAXCWND(xprt))
			cwnd = RPC_MAXCWND(xprt);
		__xprt_lock_write_next_cong(xprt);
	} else if (result == -ETIMEDOUT) {
		cwnd >>= 1;
		if (cwnd < RPC_CWNDSCALE)
			cwnd = RPC_CWNDSCALE;
	}
	dprintk("RPC:       cong %ld, cwnd was %ld, now %ld\n",
			xprt->cong, xprt->cwnd, cwnd);
	xprt->cwnd = cwnd;
	__xprt_put_cong(xprt, req);
}
EXPORT_SYMBOL_GPL(xprt_adjust_cwnd);

/**
 * xprt_wake_pending_tasks - wake all tasks on a transport's pending queue
 * @xprt: transport with waiting tasks
 * @status: result code to plant in each task before waking it
 *
 */
void xprt_wake_pending_tasks(struct rpc_xprt *xprt, int status)
{
	if (status < 0)
		rpc_wake_up_status(&xprt->pending, status);
	else
		rpc_wake_up(&xprt->pending);
}
EXPORT_SYMBOL_GPL(xprt_wake_pending_tasks);

/**
 * xprt_wait_for_buffer_space - wait for transport output buffer to clear
 * @task: task to be put to sleep
 *
 */
void xprt_wait_for_buffer_space(struct rpc_task *task)
{
	struct rpc_rqst *req = task->tk_rqstp;
	struct rpc_xprt *xprt = req->rq_xprt;

	task->tk_timeout = req->rq_timeout;
	rpc_sleep_on(&xprt->pending, task, NULL, NULL);
}
EXPORT_SYMBOL_GPL(xprt_wait_for_buffer_space);

/**
 * xprt_write_space - wake the task waiting for transport output buffer space
 * @xprt: transport with waiting tasks
 *
 * Can be called in a soft IRQ context, so xprt_write_space never sleeps.
 */
void xprt_write_space(struct rpc_xprt *xprt)
{
	if (unlikely(xprt->shutdown))
		return;

	spin_lock_bh(&xprt->transport_lock);
	if (xprt->snd_task) {
		dprintk("RPC:       write space: waking waiting task on "
				"xprt %p\n", xprt);
		rpc_wake_up_task(xprt->snd_task);
	}
	spin_unlock_bh(&xprt->transport_lock);
}
EXPORT_SYMBOL_GPL(xprt_write_space);

/**
 * xprt_set_retrans_timeout_def - set a request's retransmit timeout
 * @task: task whose timeout is to be set
 *
 * Set a request's retransmit timeout based on the transport's
 * default timeout parameters.  Used by transports that don't adjust
 * the retransmit timeout based on round-trip time estimation.
 */
void xprt_set_retrans_timeout_def(struct rpc_task *task)
{
	task->tk_timeout = task->tk_rqstp->rq_timeout;
}
EXPORT_SYMBOL_GPL(xprt_set_retrans_timeout_def);

/*
 * xprt_set_retrans_timeout_rtt - set a request's retransmit timeout
 * @task: task whose timeout is to be set
 *
 * Set a request's retransmit timeout using the RTT estimator.
 */
void xprt_set_retrans_timeout_rtt(struct rpc_task *task)
{
	int timer = task->tk_msg.rpc_proc->p_timer;
	struct rpc_rtt *rtt = task->tk_client->cl_rtt;
	struct rpc_rqst *req = task->tk_rqstp;
	unsigned long max_timeout = req->rq_xprt->timeout.to_maxval;

	task->tk_timeout = rpc_calc_rto(rtt, timer);
	task->tk_timeout <<= rpc_ntimeo(rtt, timer) + req->rq_retries;
	if (task->tk_timeout > max_timeout || task->tk_timeout == 0)
		task->tk_timeout = max_timeout;
}
EXPORT_SYMBOL_GPL(xprt_set_retrans_timeout_rtt);

static void xprt_reset_majortimeo(struct rpc_rqst *req)
{
	struct rpc_timeout *to = &req->rq_xprt->timeout;

	req->rq_majortimeo = req->rq_timeout;
	if (to->to_exponential)
		req->rq_majortimeo <<= to->to_retries;
	else
		req->rq_majortimeo += to->to_increment * to->to_retries;
	if (req->rq_majortimeo > to->to_maxval || req->rq_majortimeo == 0)
		req->rq_majortimeo = to->to_maxval;
	req->rq_majortimeo += jiffies;
}

/**
 * xprt_adjust_timeout - adjust timeout values for next retransmit
 * @req: RPC request containing parameters to use for the adjustment
 *
 */
int xprt_adjust_timeout(struct rpc_rqst *req)
{
	struct rpc_xprt *xprt = req->rq_xprt;
	struct rpc_timeout *to = &xprt->timeout;
	int status = 0;