aboutsummaryrefslogtreecommitdiffstats
path: root/net/sunrpc/xprt.c
blob: 57c5e77b155e6bf6d3aec044717239308d36705f (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
/*
 *  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_call().
 *  -	xprt_call transmits the message and installs the caller on the
 *	socket'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 socket. 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 <okir@monad.swb.de>
 */

#include <linux/module.h>

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

#include <linux/sunrpc/clnt.h>

/*
 * Local variables
 */

#ifdef RPC_DEBUG
# undef  RPC_DEBUG_DATA
# define RPCDBG_FACILITY	RPCDBG_XPRT
#endif

#define XPRT_MAX_BACKOFF	(8)

/*
 * 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 int	xprt_clear_backlog(struct rpc_xprt *xprt);

/*
 * Serialize write access to sockets, in order to prevent different
 * requests from interfering with each other.
 * Also prevents TCP socket connects from colliding with writes.
 */
static int
__xprt_lock_write(struct rpc_xprt *xprt, struct rpc_task *task)
{
	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->nocong || __xprt_get_cong(xprt, task)) {
		xprt->snd_task = task;
		if (req) {
			req->rq_bytes_sent = 0;
			req->rq_ntrans++;
		}
		return 1;
	}
	smp_mb__before_clear_bit();
	clear_bit(XPRT_LOCKED, &xprt->state);
	smp_mb__after_clear_bit();
out_sleep:
	dprintk("RPC: %4d failed to lock socket %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;
}

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

	spin_lock_bh(&xprt->transport_lock);
	retval = __xprt_lock_write(xprt, task);
	spin_unlock_bh(&xprt->transport_lock);
	return retval;
}


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

	if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
		return;
	if (!xprt->nocong && 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->nocong || __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:
	smp_mb__before_clear_bit();
	clear_bit(XPRT_LOCKED, &xprt->state);
	smp_mb__after_clear_bit();
}

/*
 * Releases the socket for use by other requests.
 */
static void
__xprt_release_write(struct rpc_xprt *xprt, struct rpc_task *task)
{
	if (xprt->snd_task == task) {
		xprt->snd_task = NULL;
		smp_mb__before_clear_bit();
		clear_bit(XPRT_LOCKED, &xprt->state);
		smp_mb__after_clear_bit();
		__xprt_lock_write_next(xprt);
	}
}

static inline void
xprt_release_write(struct rpc_xprt *xprt, struct rpc_task *task)
{
	spin_lock_bh(&xprt->transport_lock);
	__xprt_release_write(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: %4d xprt_cwnd_limited cong = %ld cwnd = %ld\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(xprt);
}

/*
 * Adjust RPC congestion window
 * We use a time-smoothed congestion estimator to avoid heavy oscillation.
 */
static void
xprt_adjust_cwnd(struct rpc_xprt *xprt, int result)
{
	unsigned long	cwnd;

	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(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;
}

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;

	if (time_before(jiffies, req->rq_majortimeo)) {
		if (to->to_exponential)
			req->rq_timeout <<= 1;
		else
			req->rq_timeout += to->to_increment;
		if (to->to_maxval && req->rq_timeout >= to->to_maxval)
			req->rq_timeout = to->to_maxval;
		req->rq_retries++;
		pprintk("RPC: %lu retrans\n", jiffies);
	} else {
		req->rq_timeout = to->to_initval;
		req->rq_retries = 0;
		xprt_reset_majortimeo(req);
		/* Reset the RTT counters == "slow start" */
		spin_lock_bh(&xprt->transport_lock);
		rpc_init_rtt(req->rq_task->tk_client->cl_rtt, to->to_initval);
		spin_unlock_bh(&xprt->transport_lock);
		pprintk("RPC: %lu timeout\n", jiffies);
		status = -ETIMEDOUT;
	}

	if (req->rq_timeout == 0) {
		printk(KERN_WARNING "xprt_adjust_timeout: rq_timeout = 0!\n");
		req->rq_timeout = 5 * HZ;
	}
	return status;
}

static void
xprt_socket_autoclose(void *args)
{
	struct rpc_xprt *xprt = (struct rpc_xprt *)args;

	xprt_disconnect(xprt);
	xprt->ops->close(xprt);
	xprt_release_write(xprt, NULL);
}

/**
 * xprt_disconnect - mark a transport as disconnected
 * @xprt: transport to flag for disconnect
 *
 */
void xprt_disconnect(struct rpc_xprt *xprt)
{
	dprintk("RPC:      disconnected transport %p\n", xprt);
	spin_lock_bh(&xprt->transport_lock);
	xprt_clear_connected(xprt);
	rpc_wake_up_status(&xprt->pending, -ENOTCONN);
	spin_unlock_bh(&xprt->transport_lock);
}

static void
xprt_init_autodisconnect(unsigned long data)
{
	struct rpc_xprt *xprt = (struct rpc_xprt *)data;

	spin_lock(&xprt->transport_lock);
	if (!list_empty(&xprt->recv) || xprt->shutdown)
		goto out_abort;
	if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
		goto out_abort;
	spin_unlock(&xprt->transport_lock);
	/* Let keventd close the socket */
	if (xprt_connecting(xprt))
		xprt_release_write(xprt, NULL);
	else
		schedule_work(&xprt->task_cleanup);
	return;
out_abort:
	spin_unlock(&xprt->transport_lock);
}

/**
 * xprt_connect - schedule a transport connect operation
 * @task: RPC task that is requesting the connect
 *
 */
void xprt_connect(struct rpc_task *task)
{
	struct rpc_xprt	*xprt = task->tk_xprt;

	dprintk("RPC: %4d xprt_connect xprt %p %s connected\n", task->tk_pid,
			xprt, (xprt_connected(xprt) ? "is" : "is not"));

	if (xprt->shutdown) {
		task->tk_status = -EIO;
		return;
	}
	if (!xprt->addr.sin_port) {
		task->tk_status = -EIO;
		return;
	}
	if (!xprt_lock_write(xprt, task))
		return;
	if (xprt_connected(xprt))
		xprt_release_write(xprt, task);
	else {
		if (task->tk_rqstp)
			task->tk_rqstp->rq_bytes_sent = 0;

		task->tk_timeout = RPC_CONNECT_TIMEOUT;
		rpc_sleep_on(&xprt->pending, task, xprt_connect_status, NULL);
		xprt->ops->connect(task);
	}
	return;
}

static void xprt_connect_status(struct rpc_task *task)
{
	struct rpc_xprt	*xprt = task->tk_xprt;

	if (task->tk_status >= 0) {
		dprintk("RPC: %4d xprt_connect_status: connection established\n",
				task->tk_pid);
		return;
	}

	switch (task->tk_status) {
	case -ECONNREFUSED:
	case -ECONNRESET:
		dprintk("RPC: %4d xprt_connect_status: server %s refused connection\n",
				task->tk_pid, task->tk_client->cl_server);
		break;
	case -ENOTCONN:
		dprintk("RPC: %4d xprt_connect_status: connection broken\n",
				task->tk_pid);
		break;
	case -ETIMEDOUT:
		dprintk("RPC: %4d xprt_connect_status: connect attempt timed out\n",
				task->tk_pid);
		break;
	default:
		dprintk("RPC: %4d xprt_connect_status: error %d connecting to server %s\n",
				task->tk_pid, -task->tk_status, task->tk_client->cl_server);
		xprt_release_write(xprt, task);
		task->tk_status = -EIO;
		return;
	}

	/* if soft mounted, just cause this RPC to fail */
	if (RPC_IS_SOFT(task)) {
		xprt_release_write(xprt, task);
		task->tk_status = -EIO;
	}
}

/**
 * xprt_lookup_rqst - find an RPC request corresponding to an XID
 * @xprt: transport on which the original request was transmitted
 * @xid: RPC XID of incoming reply
 *
 */
struct rpc_rqst *xprt_lookup_rqst(struct rpc_xprt *xprt, u32 xid)
{
	struct list_head *pos;
	struct rpc_rqst	*req = NULL;

	list_for_each(pos, &xprt->recv) {
		struct rpc_rqst *entry = list_entry(pos, struct rpc_rqst, rq_list);
		if (entry->rq_xid == xid) {
			req = entry;
			break;
		}
	}
	return req;
}

/**
 * xprt_complete_rqst - called when reply processing is complete
 * @xprt: controlling transport
 * @req: RPC request that just completed
 * @copied: actual number of bytes received from the transport
 *
 */
void xprt_complete_rqst(struct rpc_xprt *xprt, struct rpc_rqst *req, int copied)
{
	struct rpc_task	*task = req->rq_task;
	struct rpc_clnt *clnt = task->tk_client;

	/* Adjust congestion window */
	if (!xprt->nocong) {
		unsigned timer = task->tk_msg.rpc_proc->p_timer;
		xprt_adjust_cwnd(xprt, copied);
		__xprt_put_cong(xprt, req);
		if (timer) {
			if (req->rq_ntrans == 1)
				rpc_update_rtt(clnt->cl_rtt, timer,
						(long)jiffies - req->rq_xtime);
			rpc_set_timeo(clnt->cl_rtt, timer, req->rq_ntrans - 1);
		}
	}

#ifdef RPC_PROFILE
	/* Profile only reads for now */
	if (copied > 1024) {
		static unsigned long	nextstat;
		static unsigned long	pkt_rtt, pkt_len, pkt_cnt;

		pkt_cnt++;
		pkt_len += req->rq_slen + copied;
		pkt_rtt += jiffies - req->rq_xtime;
		if (time_before(nextstat, jiffies)) {
			printk("RPC: %lu %ld cwnd\n", jiffies, xprt->cwnd);
			printk("RPC: %ld %ld %ld %ld stat\n",
					jiffies, pkt_cnt, pkt_len, pkt_rtt);
			pkt_rtt = pkt_len = pkt_cnt = 0;
			nextstat = jiffies + 5 * HZ;
		}
	}
#endif

	dprintk("RPC: %4d has input (%d bytes)\n", task->tk_pid, copied);
	list_del_init(&req->rq_list);
	req->rq_received = req->rq_private_buf.len = copied;

	/* ... and wake up the process. */
	rpc_wake_up_task(task);
	return;
}

/*
 * RPC receive timeout handler.
 */
static void
xprt_timer(struct rpc_task *task)
{
	struct rpc_rqst	*req = task->tk_rqstp;
	struct rpc_xprt *xprt = req->rq_xprt;

	spin_lock(&xprt->transport_lock);
	if (req->rq_received)
		goto out;

	xprt_adjust_cwnd(req->rq_xprt, -ETIMEDOUT);
	__xprt_put_cong(xprt, req);

	dprintk("RPC: %4d xprt_timer (%s request)\n",
		task->tk_pid, req ? "pending" : "backlogged");

	task->tk_status  = -ETIMEDOUT;
out:
	task->tk_timeout = 0;
	rpc_wake_up_task(task);
	spin_unlock(&xprt->transport_lock);
}

/**
 * xprt_prepare_transmit - reserve the transport before sending a request
 * @task: RPC task about to send a request
 *
 */
int xprt_prepare_transmit(struct rpc_task *task)
{
	struct rpc_rqst	*req = task->tk_rqstp;
	struct rpc_xprt	*xprt = req->rq_xprt;
	int err = 0;

	dprintk("RPC: %4d xprt_prepare_transmit\n", task->tk_pid);

	if (xprt->shutdown)
		return -EIO;

	spin_lock_bh(&xprt->transport_lock);
	if (req->rq_received && !req->rq_bytes_sent) {
		err = req->rq_received;
		goto out_unlock;
	}
	if (!__xprt_lock_write(xprt, task)) {
		err = -EAGAIN;
		goto out_unlock;
	}

	if (!xprt_connected(xprt)) {
		err = -ENOTCONN;
		goto out_unlock;
	}
out_unlock:
	spin_unlock_bh(&xprt->transport_lock);
	return err;
}

/**
 * xprt_transmit - send an RPC request on a transport
 * @task: controlling RPC task
 *
 * We have to copy the iovec because sendmsg fiddles with its contents.
 */
void xprt_transmit(struct rpc_task *task)
{
	struct rpc_clnt *clnt = task->tk_client;
	struct rpc_rqst	*req = task->tk_rqstp;
	struct rpc_xprt	*xprt = req->rq_xprt;
	int status;

	dprintk("RPC: %4d xprt_transmit(%u)\n", task->tk_pid, req->rq_slen);

	smp_rmb();
	if (!req->rq_received) {
		if (list_empty(&req->rq_list)) {
			spin_lock_bh(&xprt->transport_lock);
			/* Update the softirq receive buffer */
			memcpy(&req->rq_private_buf, &req->rq_rcv_buf,
					sizeof(req->rq_private_buf));
			/* Add request to the receive list */
			list_add_tail(&req->rq_list, &xprt->recv);
			spin_unlock_bh(&xprt->transport_lock);
			xprt_reset_majortimeo(req);
			/* Turn off autodisconnect */
			del_singleshot_timer_sync(&xprt->timer);
		}
	} else if (!req->rq_bytes_sent)
		return;

	status = xprt->ops->send_request(task);
	if (!status)
		goto out_receive;

	/* Note: at this point, task->tk_sleeping has not yet been set,
	 *	 hence there is no danger of the waking up task being put on
	 *	 schedq, and being picked up by a parallel run of rpciod().
	 */
	task->tk_status = status;

	switch (status) {
	case -ECONNREFUSED:
		task->tk_timeout = RPC_REESTABLISH_TIMEOUT;
		rpc_sleep_on(&xprt->sending, task, NULL, NULL);
	case -EAGAIN:
	case -ENOTCONN:
		return;
	default:
		if (xprt->stream)
			xprt_disconnect(xprt);
	}
	xprt_release_write(xprt, task);
	return;
 out_receive:
	dprintk("RPC: %4d xmit complete\n", task->tk_pid);
	/* Set the task's receive timeout value */
	spin_lock_bh(&xprt->transport_lock);
	if (!xprt->nocong) {
		int timer = task->tk_msg.rpc_proc->p_timer;
		task->tk_timeout = rpc_calc_rto(clnt->cl_rtt, timer);
		task->tk_timeout <<= rpc_ntimeo(clnt->cl_rtt, timer) + req->rq_retries;
		if (task->tk_timeout > xprt->timeout.to_maxval || task->tk_timeout == 0)
			task->tk_timeout = xprt->timeout.to_maxval;
	} else
		task->tk_timeout = req->rq_timeout;
	/* Don't race with disconnect */
	if (!xprt_connected(xprt))
		task->tk_status = -ENOTCONN;
	else if (!req->rq_received)
		rpc_sleep_on(&xprt->pending, task, NULL, xprt_timer);
	__xprt_release_write(xprt, task);
	spin_unlock_bh(&xprt->transport_lock);
}

static inline void do_xprt_reserve(struct rpc_task *task)
{
	struct rpc_xprt	*xprt = task->tk_xprt;

	task->tk_status = 0;
	if (task->tk_rqstp)
		return;
	if (!list_empty(&xprt->free)) {
		struct rpc_rqst	*req = list_entry(xprt->free.next, struct rpc_rqst, rq_list);
		list_del_init(&req->rq_list);
		task->tk_rqstp = req;
		xprt_request_init(task, xprt);
		return;
	}
	dprintk("RPC:      waiting for request slot\n");
	task->tk_status = -EAGAIN;
	task->tk_timeout = 0;
	rpc_sleep_on(&xprt->backlog, task, NULL, NULL);
}

/**
 * xprt_reserve - allocate an RPC request slot
 * @task: RPC task requesting a slot allocation
 *
 * If no more slots are available, place the task on the transport's
 * backlog queue.
 */
void xprt_reserve(struct rpc_task *task)
{
	struct rpc_xprt	*xprt = task->tk_xprt;

	task->tk_status = -EIO;
	if (!xprt->shutdown) {
		spin_lock(&xprt->reserve_lock);
		do_xprt_reserve(task);
		spin_unlock(&xprt->reserve_lock);
	}
}

static inline u32 xprt_alloc_xid(struct rpc_xprt *xprt)
{
	return xprt->xid++;
}

static inline void xprt_init_xid(struct rpc_xprt *xprt)
{
	get_random_bytes(&xprt->xid, sizeof(xprt->xid));
}

static void xprt_request_init(struct rpc_task *task, struct rpc_xprt *xprt)
{
	struct rpc_rqst	*req = task->tk_rqstp;

	req->rq_timeout = xprt->timeout.to_initval;
	req->rq_task	= task;
	req->rq_xprt    = xprt;
	req->rq_xid     = xprt_alloc_xid(xprt);
	dprintk("RPC: %4d reserved req %p xid %08x\n", task->tk_pid,
			req, ntohl(req->rq_xid));
}

/**
 * xprt_release - release an RPC request slot
 * @task: task which is finished with the slot
 *
 */
void xprt_release(struct rpc_task *task)
{
	struct rpc_xprt	*xprt = task->tk_xprt;
	struct rpc_rqst	*req;

	if (!(req = task->tk_rqstp))
		return;
	spin_lock_bh(&xprt->transport_lock);
	__xprt_release_write(xprt, task);
	__xprt_put_cong(xprt, req);
	if (!list_empty(&req->rq_list))
		list_del(&req->rq_list);
	xprt->last_used = jiffies;
	if (list_empty(&xprt->recv) && !xprt->shutdown)
		mod_timer(&xprt->timer,
				xprt->last_used + RPC_IDLE_DISCONNECT_TIMEOUT);
	spin_unlock_bh(&xprt->transport_lock);
	task->tk_rqstp = NULL;
	memset(req, 0, sizeof(*req));	/* mark unused */

	dprintk("RPC: %4d release request %p\n", task->tk_pid, req);

	spin_lock(&xprt->reserve_lock);
	list_add(&req->rq_list, &xprt->free);
	xprt_clear_backlog(xprt);
	spin_unlock(&xprt->reserve_lock);
}

/**
 * xprt_set_timeout - set constant RPC timeout
 * @to: RPC timeout parameters to set up
 * @retr: number of retries
 * @incr: amount of increase after each retry
 *
 */
void xprt_set_timeout(struct rpc_timeout *to, unsigned int retr, unsigned long incr)
{
	to->to_initval   = 
	to->to_increment = incr;
	to->to_maxval    = to->to_initval + (incr * retr);
	to->to_retries   = retr;
	to->to_exponential = 0;
}

static struct rpc_xprt *xprt_setup(int proto, struct sockaddr_in *ap, struct rpc_timeout *to)
{
	int result;
	struct rpc_xprt	*xprt;
	struct rpc_rqst	*req;

	if ((xprt = kmalloc(sizeof(struct rpc_xprt), GFP_KERNEL)) == NULL)
		return ERR_PTR(-ENOMEM);
	memset(xprt, 0, sizeof(*xprt)); /* Nnnngh! */

	xprt->addr = *ap;

	switch (proto) {
	case IPPROTO_UDP:
		result = xs_setup_udp(xprt, to);
		break;
	case IPPROTO_TCP:
		result = xs_setup_tcp(xprt, to);
		break;
	default:
		printk(KERN_ERR "RPC: unrecognized transport protocol: %d\n",
				proto);
		result = -EIO;
		break;
	}
	if (result) {
		kfree(xprt);
		return ERR_PTR(result);
	}

	spin_lock_init(&xprt->transport_lock);
	spin_lock_init(&xprt->reserve_lock);
	init_waitqueue_head(&xprt->cong_wait);

	INIT_LIST_HEAD(&xprt->free);
	INIT_LIST_HEAD(&xprt->recv);
	INIT_WORK(&xprt->task_cleanup, xprt_socket_autoclose, xprt);
	init_timer(&xprt->timer);
	xprt->timer.function = xprt_init_autodisconnect;
	xprt->timer.data = (unsigned long) xprt;
	xprt->last_used = jiffies;

	rpc_init_wait_queue(&xprt->pending, "xprt_pending");
	rpc_init_wait_queue(&xprt->sending, "xprt_sending");
	rpc_init_wait_queue(&xprt->resend, "xprt_resend");
	rpc_init_priority_wait_queue(&xprt->backlog, "xprt_backlog");

	/* initialize free list */
	for (req = &xprt->slot[xprt->max_reqs-1]; req >= &xprt->slot[0]; req--)
		list_add(&req->rq_list, &xprt->free);

	xprt_init_xid(xprt);

	dprintk("RPC:      created transport %p with %u slots\n", xprt,
			xprt->max_reqs);
	
	return xprt;
}

/**
 * xprt_create_proto - create an RPC client transport
 * @proto: requested transport protocol
 * @sap: remote peer's address
 * @to: timeout parameters for new transport
 *
 */
struct rpc_xprt *xprt_create_proto(int proto, struct sockaddr_in *sap, struct rpc_timeout *to)
{
	struct rpc_xprt	*xprt;

	xprt = xprt_setup(proto, sap, to);
	if (IS_ERR(xprt))
		dprintk("RPC:      xprt_create_proto failed\n");
	else
		dprintk("RPC:      xprt_create_proto created xprt %p\n", xprt);
	return xprt;
}

static void xprt_shutdown(struct rpc_xprt *xprt)
{
	xprt->shutdown = 1;
	rpc_wake_up(&xprt->sending);
	rpc_wake_up(&xprt->resend);
	rpc_wake_up(&xprt->pending);
	rpc_wake_up(&xprt->backlog);
	wake_up(&xprt->cong_wait);
	del_timer_sync(&xprt->timer);
}

static int xprt_clear_backlog(struct rpc_xprt *xprt) {
	rpc_wake_up_next(&xprt->backlog);
	wake_up(&xprt->cong_wait);
	return 1;
}

/**
 * xprt_destroy - destroy an RPC transport, killing off all requests.
 * @xprt: transport to destroy
 *
 */
int xprt_destroy(struct rpc_xprt *xprt)
{
	dprintk("RPC:      destroying transport %p\n", xprt);
	xprt_shutdown(xprt);
	xprt->ops->destroy(xprt);
	kfree(xprt);

	return 0;
}