summaryrefslogtreecommitdiffstats
path: root/sys/kern/kern_alq.c
blob: 7f8c6033052858c3defcc9af5f7148e0969a3c3c (plain)
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
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
/*-
 * Copyright (c) 2002, Jeffrey Roberson <jeff@freebsd.org>
 * Copyright (c) 2008-2009, Lawrence Stewart <lstewart@freebsd.org>
 * Copyright (c) 2009-2010, The FreeBSD Foundation
 * All rights reserved.
 *
 * Portions of this software were developed at the Centre for Advanced
 * Internet Architectures, Swinburne University of Technology, Melbourne,
 * Australia by Lawrence Stewart under sponsorship from the FreeBSD Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice unmodified, this list of conditions, and the following
 *    disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_mac.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/kthread.h>
#include <sys/lock.h>
#include <sys/mount.h>
#include <sys/mutex.h>
#include <sys/namei.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/alq.h>
#include <sys/malloc.h>
#include <sys/unistd.h>
#include <sys/fcntl.h>
#include <sys/eventhandler.h>

#include <security/mac/mac_framework.h>

/* Async. Logging Queue */
struct alq {
	char	*aq_entbuf;		/* Buffer for stored entries */
	int	aq_entmax;		/* Max entries */
	int	aq_entlen;		/* Entry length */
	int	aq_freebytes;		/* Bytes available in buffer */
	int	aq_buflen;		/* Total length of our buffer */
	int	aq_writehead;		/* Location for next write */
	int	aq_writetail;		/* Flush starts at this location */
	int	aq_wrapearly;		/* # bytes left blank at end of buf */
	int	aq_flags;		/* Queue flags */
	int	aq_waiters;		/* Num threads waiting for resources
					 * NB: Used as a wait channel so must
					 * not be first field in the alq struct
					 */
	struct	ale	aq_getpost;	/* ALE for use by get/post */
	struct mtx	aq_mtx;		/* Queue lock */
	struct vnode	*aq_vp;		/* Open vnode handle */
	struct ucred	*aq_cred;	/* Credentials of the opening thread */
	LIST_ENTRY(alq)	aq_act;		/* List of active queues */
	LIST_ENTRY(alq)	aq_link;	/* List of all queues */
};

#define	AQ_WANTED	0x0001		/* Wakeup sleeper when io is done */
#define	AQ_ACTIVE	0x0002		/* on the active list */
#define	AQ_FLUSHING	0x0004		/* doing IO */
#define	AQ_SHUTDOWN	0x0008		/* Queue no longer valid */
#define	AQ_ORDERED	0x0010		/* Queue enforces ordered writes */
#define	AQ_LEGACY	0x0020		/* Legacy queue (fixed length writes) */

#define	ALQ_LOCK(alq)	mtx_lock_spin(&(alq)->aq_mtx)
#define	ALQ_UNLOCK(alq)	mtx_unlock_spin(&(alq)->aq_mtx)

#define HAS_PENDING_DATA(alq) ((alq)->aq_freebytes != (alq)->aq_buflen)

static MALLOC_DEFINE(M_ALD, "ALD", "ALD");

/*
 * The ald_mtx protects the ald_queues list and the ald_active list.
 */
static struct mtx ald_mtx;
static LIST_HEAD(, alq) ald_queues;
static LIST_HEAD(, alq) ald_active;
static int ald_shutingdown = 0;
struct thread *ald_thread;
static struct proc *ald_proc;
static eventhandler_tag alq_eventhandler_tag = NULL;

#define	ALD_LOCK()	mtx_lock(&ald_mtx)
#define	ALD_UNLOCK()	mtx_unlock(&ald_mtx)

/* Daemon functions */
static int ald_add(struct alq *);
static int ald_rem(struct alq *);
static void ald_startup(void *);
static void ald_daemon(void);
static void ald_shutdown(void *, int);
static void ald_activate(struct alq *);
static void ald_deactivate(struct alq *);

/* Internal queue functions */
static void alq_shutdown(struct alq *);
static void alq_destroy(struct alq *);
static int alq_doio(struct alq *);


/*
 * Add a new queue to the global list.  Fail if we're shutting down.
 */
static int
ald_add(struct alq *alq)
{
	int error;

	error = 0;

	ALD_LOCK();
	if (ald_shutingdown) {
		error = EBUSY;
		goto done;
	}
	LIST_INSERT_HEAD(&ald_queues, alq, aq_link);
done:
	ALD_UNLOCK();
	return (error);
}

/*
 * Remove a queue from the global list unless we're shutting down.  If so,
 * the ald will take care of cleaning up it's resources.
 */
static int
ald_rem(struct alq *alq)
{
	int error;

	error = 0;

	ALD_LOCK();
	if (ald_shutingdown) {
		error = EBUSY;
		goto done;
	}
	LIST_REMOVE(alq, aq_link);
done:
	ALD_UNLOCK();
	return (error);
}

/*
 * Put a queue on the active list.  This will schedule it for writing.
 */
static void
ald_activate(struct alq *alq)
{
	LIST_INSERT_HEAD(&ald_active, alq, aq_act);
	wakeup(&ald_active);
}

static void
ald_deactivate(struct alq *alq)
{
	LIST_REMOVE(alq, aq_act);
	alq->aq_flags &= ~AQ_ACTIVE;
}

static void
ald_startup(void *unused)
{
	mtx_init(&ald_mtx, "ALDmtx", NULL, MTX_DEF|MTX_QUIET);
	LIST_INIT(&ald_queues);
	LIST_INIT(&ald_active);
}

static void
ald_daemon(void)
{
	int needwakeup;
	struct alq *alq;

	ald_thread = FIRST_THREAD_IN_PROC(ald_proc);

	alq_eventhandler_tag = EVENTHANDLER_REGISTER(shutdown_pre_sync,
	    ald_shutdown, NULL, SHUTDOWN_PRI_FIRST);

	ALD_LOCK();

	for (;;) {
		while ((alq = LIST_FIRST(&ald_active)) == NULL &&
		    !ald_shutingdown)
			mtx_sleep(&ald_active, &ald_mtx, PWAIT, "aldslp", 0);

		/* Don't shutdown until all active ALQs are flushed. */
		if (ald_shutingdown && alq == NULL) {
			ALD_UNLOCK();
			break;
		}

		ALQ_LOCK(alq);
		ald_deactivate(alq);
		ALD_UNLOCK();
		needwakeup = alq_doio(alq);
		ALQ_UNLOCK(alq);
		if (needwakeup)
			wakeup_one(alq);
		ALD_LOCK();
	}

	kproc_exit(0);
}

static void
ald_shutdown(void *arg, int howto)
{
	struct alq *alq;

	ALD_LOCK();

	/* Ensure no new queues can be created. */
	ald_shutingdown = 1;

	/* Shutdown all ALQs prior to terminating the ald_daemon. */
	while ((alq = LIST_FIRST(&ald_queues)) != NULL) {
		LIST_REMOVE(alq, aq_link);
		ALD_UNLOCK();
		alq_shutdown(alq);
		ALD_LOCK();
	}

	/* At this point, all ALQs are flushed and shutdown. */

	/*
	 * Wake ald_daemon so that it exits. It won't be able to do
	 * anything until we mtx_sleep because we hold the ald_mtx.
	 */
	wakeup(&ald_active);

	/* Wait for ald_daemon to exit. */
	mtx_sleep(ald_proc, &ald_mtx, PWAIT, "aldslp", 0);

	ALD_UNLOCK();
}

static void
alq_shutdown(struct alq *alq)
{
	ALQ_LOCK(alq);

	/* Stop any new writers. */
	alq->aq_flags |= AQ_SHUTDOWN;

	/*
	 * If the ALQ isn't active but has unwritten data (possible if
	 * the ALQ_NOACTIVATE flag has been used), explicitly activate the
	 * ALQ here so that the pending data gets flushed by the ald_daemon.
	 */
	if (!(alq->aq_flags & AQ_ACTIVE) && HAS_PENDING_DATA(alq)) {
		alq->aq_flags |= AQ_ACTIVE;
		ALQ_UNLOCK(alq);
		ALD_LOCK();
		ald_activate(alq);
		ALD_UNLOCK();
		ALQ_LOCK(alq);
	}

	/* Drain IO */
	while (alq->aq_flags & AQ_ACTIVE) {
		alq->aq_flags |= AQ_WANTED;
		msleep_spin(alq, &alq->aq_mtx, "aldclose", 0);
	}
	ALQ_UNLOCK(alq);

	vn_close(alq->aq_vp, FWRITE, alq->aq_cred,
	    curthread);
	crfree(alq->aq_cred);
}

void
alq_destroy(struct alq *alq)
{
	/* Drain all pending IO. */
	alq_shutdown(alq);

	mtx_destroy(&alq->aq_mtx);
	free(alq->aq_entbuf, M_ALD);
	free(alq, M_ALD);
}

/*
 * Flush all pending data to disk.  This operation will block.
 */
static int
alq_doio(struct alq *alq)
{
	struct thread *td;
	struct mount *mp;
	struct vnode *vp;
	struct uio auio;
	struct iovec aiov[2];
	int totlen;
	int iov;
	int wrapearly;

	KASSERT((HAS_PENDING_DATA(alq)), ("%s: queue empty!", __func__));

	vp = alq->aq_vp;
	td = curthread;
	totlen = 0;
	iov = 1;
	wrapearly = alq->aq_wrapearly;

	bzero(&aiov, sizeof(aiov));
	bzero(&auio, sizeof(auio));

	/* Start the write from the location of our buffer tail pointer. */
	aiov[0].iov_base = alq->aq_entbuf + alq->aq_writetail;

	if (alq->aq_writetail < alq->aq_writehead) {
		/* Buffer not wrapped. */
		totlen = aiov[0].iov_len = alq->aq_writehead - alq->aq_writetail;
	} else if (alq->aq_writehead == 0) {
		/* Buffer not wrapped (special case to avoid an empty iov). */
		totlen = aiov[0].iov_len = alq->aq_buflen - alq->aq_writetail -
		    wrapearly;
	} else {
		/*
		 * Buffer wrapped, requires 2 aiov entries:
		 * - first is from writetail to end of buffer
		 * - second is from start of buffer to writehead
		 */
		aiov[0].iov_len = alq->aq_buflen - alq->aq_writetail -
		    wrapearly;
		iov++;
		aiov[1].iov_base = alq->aq_entbuf;
		aiov[1].iov_len =  alq->aq_writehead;
		totlen = aiov[0].iov_len + aiov[1].iov_len;
	}

	alq->aq_flags |= AQ_FLUSHING;
	ALQ_UNLOCK(alq);

	auio.uio_iov = &aiov[0];
	auio.uio_offset = 0;
	auio.uio_segflg = UIO_SYSSPACE;
	auio.uio_rw = UIO_WRITE;
	auio.uio_iovcnt = iov;
	auio.uio_resid = totlen;
	auio.uio_td = td;

	/*
	 * Do all of the junk required to write now.
	 */
	vn_start_write(vp, &mp, V_WAIT);
	vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
	/*
	 * XXX: VOP_WRITE error checks are ignored.
	 */
#ifdef MAC
	if (mac_vnode_check_write(alq->aq_cred, NOCRED, vp) == 0)
#endif
		VOP_WRITE(vp, &auio, IO_UNIT | IO_APPEND, alq->aq_cred);
	VOP_UNLOCK(vp, 0);
	vn_finished_write(mp);

	ALQ_LOCK(alq);
	alq->aq_flags &= ~AQ_FLUSHING;

	/* Adjust writetail as required, taking into account wrapping. */
	alq->aq_writetail = (alq->aq_writetail + totlen + wrapearly) %
	    alq->aq_buflen;
	alq->aq_freebytes += totlen + wrapearly;

	/*
	 * If we just flushed part of the buffer which wrapped, reset the
	 * wrapearly indicator.
	 */
	if (wrapearly)
		alq->aq_wrapearly = 0;

	/*
	 * If we just flushed the buffer completely, reset indexes to 0 to
	 * minimise buffer wraps.
	 * This is also required to ensure alq_getn() can't wedge itself.
	 */
	if (!HAS_PENDING_DATA(alq))
		alq->aq_writehead = alq->aq_writetail = 0;

	KASSERT((alq->aq_writetail >= 0 && alq->aq_writetail < alq->aq_buflen),
	    ("%s: aq_writetail < 0 || aq_writetail >= aq_buflen", __func__));

	if (alq->aq_flags & AQ_WANTED) {
		alq->aq_flags &= ~AQ_WANTED;
		return (1);
	}

	return(0);
}

static struct kproc_desc ald_kp = {
        "ALQ Daemon",
        ald_daemon,
        &ald_proc
};

SYSINIT(aldthread, SI_SUB_KTHREAD_IDLE, SI_ORDER_ANY, kproc_start, &ald_kp);
SYSINIT(ald, SI_SUB_LOCK, SI_ORDER_ANY, ald_startup, NULL);


/* User visible queue functions */

/*
 * Create the queue data structure, allocate the buffer, and open the file.
 */

int
alq_open_flags(struct alq **alqp, const char *file, struct ucred *cred, int cmode,
    int size, int flags)
{
	struct thread *td;
	struct nameidata nd;
	struct alq *alq;
	int oflags;
	int error;

	KASSERT((size > 0), ("%s: size <= 0", __func__));

	*alqp = NULL;
	td = curthread;

	NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_SYSSPACE, file, td);
	oflags = FWRITE | O_NOFOLLOW | O_CREAT;

	error = vn_open_cred(&nd, &oflags, cmode, 0, cred, NULL);
	if (error)
		return (error);

	NDFREE(&nd, NDF_ONLY_PNBUF);
	/* We just unlock so we hold a reference */
	VOP_UNLOCK(nd.ni_vp, 0);

	alq = malloc(sizeof(*alq), M_ALD, M_WAITOK|M_ZERO);
	alq->aq_vp = nd.ni_vp;
	alq->aq_cred = crhold(cred);

	mtx_init(&alq->aq_mtx, "ALD Queue", NULL, MTX_SPIN|MTX_QUIET);

	alq->aq_buflen = size;
	alq->aq_entmax = 0;
	alq->aq_entlen = 0;

	alq->aq_freebytes = alq->aq_buflen;
	alq->aq_entbuf = malloc(alq->aq_buflen, M_ALD, M_WAITOK|M_ZERO);
	alq->aq_writehead = alq->aq_writetail = 0;
	if (flags & ALQ_ORDERED)
		alq->aq_flags |= AQ_ORDERED;

	if ((error = ald_add(alq)) != 0) {
		alq_destroy(alq);
		return (error);
	}

	*alqp = alq;

	return (0);
}

int
alq_open(struct alq **alqp, const char *file, struct ucred *cred, int cmode,
    int size, int count)
{
	int ret;

	KASSERT((count >= 0), ("%s: count < 0", __func__));

	if (count > 0) {
		if ((ret = alq_open_flags(alqp, file, cred, cmode,
		    size*count, 0)) == 0) {
			(*alqp)->aq_flags |= AQ_LEGACY;
			(*alqp)->aq_entmax = count;
			(*alqp)->aq_entlen = size;
		}
	} else
		ret = alq_open_flags(alqp, file, cred, cmode, size, 0);

	return (ret);
}


/*
 * Copy a new entry into the queue.  If the operation would block either
 * wait or return an error depending on the value of waitok.
 */
int
alq_writen(struct alq *alq, void *data, int len, int flags)
{
	int activate, copy, ret;
	void *waitchan;

	KASSERT((len > 0 && len <= alq->aq_buflen),
	    ("%s: len <= 0 || len > aq_buflen", __func__));

	activate = ret = 0;
	copy = len;
	waitchan = NULL;

	ALQ_LOCK(alq);

	/*
	 * Fail to perform the write and return EWOULDBLOCK if:
	 * - The message is larger than our underlying buffer.
	 * - The ALQ is being shutdown.
	 * - There is insufficient free space in our underlying buffer
	 *   to accept the message and the user can't wait for space.
	 * - There is insufficient free space in our underlying buffer
	 *   to accept the message and the alq is inactive due to prior
	 *   use of the ALQ_NOACTIVATE flag (which would lead to deadlock).
	 */
	if (len > alq->aq_buflen ||
	    alq->aq_flags & AQ_SHUTDOWN ||
	    (((flags & ALQ_NOWAIT) || (!(alq->aq_flags & AQ_ACTIVE) &&
	    HAS_PENDING_DATA(alq))) && alq->aq_freebytes < len)) {
		ALQ_UNLOCK(alq);
		return (EWOULDBLOCK);
	}

	/*
	 * If we want ordered writes and there is already at least one thread
	 * waiting for resources to become available, sleep until we're woken.
	 */
	if (alq->aq_flags & AQ_ORDERED && alq->aq_waiters > 0) {
		KASSERT(!(flags & ALQ_NOWAIT),
		    ("%s: ALQ_NOWAIT set but incorrectly ignored!", __func__));
		alq->aq_waiters++;
		msleep_spin(&alq->aq_waiters, &alq->aq_mtx, "alqwnord", 0);
		alq->aq_waiters--;
	}

	/*
	 * (ALQ_WAITOK && aq_freebytes < len) or aq_freebytes >= len, either
	 * enter while loop and sleep until we have enough free bytes (former)
	 * or skip (latter). If AQ_ORDERED is set, only 1 thread at a time will
	 * be in this loop. Otherwise, multiple threads may be sleeping here
	 * competing for ALQ resources.
	 */
	while (alq->aq_freebytes < len && !(alq->aq_flags & AQ_SHUTDOWN)) {
		KASSERT(!(flags & ALQ_NOWAIT),
		    ("%s: ALQ_NOWAIT set but incorrectly ignored!", __func__));
		alq->aq_flags |= AQ_WANTED;
		alq->aq_waiters++;
		if (waitchan)
			wakeup(waitchan);
		msleep_spin(alq, &alq->aq_mtx, "alqwnres", 0);
		alq->aq_waiters--;

		/*
		 * If we're the first thread to wake after an AQ_WANTED wakeup
		 * but there isn't enough free space for us, we're going to loop
		 * and sleep again. If there are other threads waiting in this
		 * loop, schedule a wakeup so that they can see if the space
		 * they require is available.
		 */
		if (alq->aq_waiters > 0 && !(alq->aq_flags & AQ_ORDERED) &&
		    alq->aq_freebytes < len && !(alq->aq_flags & AQ_WANTED))
			waitchan = alq;
		else
			waitchan = NULL;
	}

	/*
	 * If there are waiters, we need to signal the waiting threads after we
	 * complete our work. The alq ptr is used as a wait channel for threads
	 * requiring resources to be freed up. In the AQ_ORDERED case, threads
	 * are not allowed to concurrently compete for resources in the above
	 * while loop, so we use a different wait channel in this case.
	 */
	if (alq->aq_waiters > 0) {
		if (alq->aq_flags & AQ_ORDERED)
			waitchan = &alq->aq_waiters;
		else
			waitchan = alq;
	} else
		waitchan = NULL;

	/* Bail if we're shutting down. */
	if (alq->aq_flags & AQ_SHUTDOWN) {
		ret = EWOULDBLOCK;
		goto unlock;
	}

	/*
	 * If we need to wrap the buffer to accommodate the write,
	 * we'll need 2 calls to bcopy.
	 */
	if ((alq->aq_buflen - alq->aq_writehead) < len)
		copy = alq->aq_buflen - alq->aq_writehead;

	/* Copy message (or part thereof if wrap required) to the buffer. */
	bcopy(data, alq->aq_entbuf + alq->aq_writehead, copy);
	alq->aq_writehead += copy;

	if (alq->aq_writehead >= alq->aq_buflen) {
		KASSERT((alq->aq_writehead == alq->aq_buflen),
		    ("%s: alq->aq_writehead (%d) > alq->aq_buflen (%d)",
		    __func__,
		    alq->aq_writehead,
		    alq->aq_buflen));
		alq->aq_writehead = 0;
	}

	if (copy != len) {
		/*
		 * Wrap the buffer by copying the remainder of our message
		 * to the start of the buffer and resetting aq_writehead.
		 */
		bcopy(((uint8_t *)data)+copy, alq->aq_entbuf, len - copy);
		alq->aq_writehead = len - copy;
	}

	KASSERT((alq->aq_writehead >= 0 && alq->aq_writehead < alq->aq_buflen),
	    ("%s: aq_writehead < 0 || aq_writehead >= aq_buflen", __func__));

	alq->aq_freebytes -= len;

	if (!(alq->aq_flags & AQ_ACTIVE) && !(flags & ALQ_NOACTIVATE)) {
		alq->aq_flags |= AQ_ACTIVE;
		activate = 1;
	}

	KASSERT((HAS_PENDING_DATA(alq)), ("%s: queue empty!", __func__));

unlock:
	ALQ_UNLOCK(alq);

	if (activate) {
		ALD_LOCK();
		ald_activate(alq);
		ALD_UNLOCK();
	}

	/* NB: We rely on wakeup_one waking threads in a FIFO manner. */
	if (waitchan != NULL)
		wakeup_one(waitchan);

	return (ret);
}

int
alq_write(struct alq *alq, void *data, int flags)
{
	/* Should only be called in fixed length message (legacy) mode. */
	KASSERT((alq->aq_flags & AQ_LEGACY),
	    ("%s: fixed length write on variable length queue", __func__));
	return (alq_writen(alq, data, alq->aq_entlen, flags));
}

/*
 * Retrieve a pointer for the ALQ to write directly into, avoiding bcopy.
 */
struct ale *
alq_getn(struct alq *alq, int len, int flags)
{
	int contigbytes;
	void *waitchan;

	KASSERT((len > 0 && len <= alq->aq_buflen),
	    ("%s: len <= 0 || len > alq->aq_buflen", __func__));

	waitchan = NULL;

	ALQ_LOCK(alq);

	/*
	 * Determine the number of free contiguous bytes.
	 * We ensure elsewhere that if aq_writehead == aq_writetail because
	 * the buffer is empty, they will both be set to 0 and therefore
	 * aq_freebytes == aq_buflen and is fully contiguous.
	 * If they are equal and the buffer is not empty, aq_freebytes will
	 * be 0 indicating the buffer is full.
	 */
	if (alq->aq_writehead <= alq->aq_writetail)
		contigbytes = alq->aq_freebytes;
	else {
		contigbytes = alq->aq_buflen - alq->aq_writehead;

		if (contigbytes < len) {
			/*
			 * Insufficient space at end of buffer to handle a
			 * contiguous write. Wrap early if there's space at
			 * the beginning. This will leave a hole at the end
			 * of the buffer which we will have to skip over when
			 * flushing the buffer to disk.
			 */
			if (alq->aq_writetail >= len || flags & ALQ_WAITOK) {
				/* Keep track of # bytes left blank. */
				alq->aq_wrapearly = contigbytes;
				/* Do the wrap and adjust counters. */
				contigbytes = alq->aq_freebytes =
				    alq->aq_writetail;
				alq->aq_writehead = 0;
			}
		}
	}

	/*
	 * Return a NULL ALE if:
	 * - The message is larger than our underlying buffer.
	 * - The ALQ is being shutdown.
	 * - There is insufficient free space in our underlying buffer
	 *   to accept the message and the user can't wait for space.
	 * - There is insufficient free space in our underlying buffer
	 *   to accept the message and the alq is inactive due to prior
	 *   use of the ALQ_NOACTIVATE flag (which would lead to deadlock).
	 */
	if (len > alq->aq_buflen ||
	    alq->aq_flags & AQ_SHUTDOWN ||
	    (((flags & ALQ_NOWAIT) || (!(alq->aq_flags & AQ_ACTIVE) &&
	    HAS_PENDING_DATA(alq))) && contigbytes < len)) {
		ALQ_UNLOCK(alq);
		return (NULL);
	}

	/*
	 * If we want ordered writes and there is already at least one thread
	 * waiting for resources to become available, sleep until we're woken.
	 */
	if (alq->aq_flags & AQ_ORDERED && alq->aq_waiters > 0) {
		KASSERT(!(flags & ALQ_NOWAIT),
		    ("%s: ALQ_NOWAIT set but incorrectly ignored!", __func__));
		alq->aq_waiters++;
		msleep_spin(&alq->aq_waiters, &alq->aq_mtx, "alqgnord", 0);
		alq->aq_waiters--;
	}

	/*
	 * (ALQ_WAITOK && contigbytes < len) or contigbytes >= len, either enter
	 * while loop and sleep until we have enough contiguous free bytes
	 * (former) or skip (latter). If AQ_ORDERED is set, only 1 thread at a
	 * time will be in this loop. Otherwise, multiple threads may be
	 * sleeping here competing for ALQ resources.
	 */
	while (contigbytes < len && !(alq->aq_flags & AQ_SHUTDOWN)) {
		KASSERT(!(flags & ALQ_NOWAIT),
		    ("%s: ALQ_NOWAIT set but incorrectly ignored!", __func__));
		alq->aq_flags |= AQ_WANTED;
		alq->aq_waiters++;
		if (waitchan)
			wakeup(waitchan);
		msleep_spin(alq, &alq->aq_mtx, "alqgnres", 0);
		alq->aq_waiters--;

		if (alq->aq_writehead <= alq->aq_writetail)
			contigbytes = alq->aq_freebytes;
		else
			contigbytes = alq->aq_buflen - alq->aq_writehead;

		/*
		 * If we're the first thread to wake after an AQ_WANTED wakeup
		 * but there isn't enough free space for us, we're going to loop
		 * and sleep again. If there are other threads waiting in this
		 * loop, schedule a wakeup so that they can see if the space
		 * they require is available.
		 */
		if (alq->aq_waiters > 0 && !(alq->aq_flags & AQ_ORDERED) &&
		    contigbytes < len && !(alq->aq_flags & AQ_WANTED))
			waitchan = alq;
		else
			waitchan = NULL;
	}

	/*
	 * If there are waiters, we need to signal the waiting threads after we
	 * complete our work. The alq ptr is used as a wait channel for threads
	 * requiring resources to be freed up. In the AQ_ORDERED case, threads
	 * are not allowed to concurrently compete for resources in the above
	 * while loop, so we use a different wait channel in this case.
	 */
	if (alq->aq_waiters > 0) {
		if (alq->aq_flags & AQ_ORDERED)
			waitchan = &alq->aq_waiters;
		else
			waitchan = alq;
	} else
		waitchan = NULL;

	/* Bail if we're shutting down. */
	if (alq->aq_flags & AQ_SHUTDOWN) {
		ALQ_UNLOCK(alq);
		if (waitchan != NULL)
			wakeup_one(waitchan);
		return (NULL);
	}

	/*
	 * If we are here, we have a contiguous number of bytes >= len
	 * available in our buffer starting at aq_writehead.
	 */
	alq->aq_getpost.ae_data = alq->aq_entbuf + alq->aq_writehead;
	alq->aq_getpost.ae_bytesused = len;

	return (&alq->aq_getpost);
}

struct ale *
alq_get(struct alq *alq, int flags)
{
	/* Should only be called in fixed length message (legacy) mode. */
	KASSERT((alq->aq_flags & AQ_LEGACY),
	    ("%s: fixed length get on variable length queue", __func__));
	return (alq_getn(alq, alq->aq_entlen, flags));
}

void
alq_post_flags(struct alq *alq, struct ale *ale, int flags)
{
	int activate;
	void *waitchan;

	activate = 0;

	if (ale->ae_bytesused > 0) {
		if (!(alq->aq_flags & AQ_ACTIVE) &&
		    !(flags & ALQ_NOACTIVATE)) {
			alq->aq_flags |= AQ_ACTIVE;
			activate = 1;
		}

		alq->aq_writehead += ale->ae_bytesused;
		alq->aq_freebytes -= ale->ae_bytesused;

		/* Wrap aq_writehead if we filled to the end of the buffer. */
		if (alq->aq_writehead == alq->aq_buflen)
			alq->aq_writehead = 0;

		KASSERT((alq->aq_writehead >= 0 &&
		    alq->aq_writehead < alq->aq_buflen),
		    ("%s: aq_writehead < 0 || aq_writehead >= aq_buflen",
		    __func__));

		KASSERT((HAS_PENDING_DATA(alq)), ("%s: queue empty!", __func__));
	}

	/*
	 * If there are waiters, we need to signal the waiting threads after we
	 * complete our work. The alq ptr is used as a wait channel for threads
	 * requiring resources to be freed up. In the AQ_ORDERED case, threads
	 * are not allowed to concurrently compete for resources in the
	 * alq_getn() while loop, so we use a different wait channel in this case.
	 */
	if (alq->aq_waiters > 0) {
		if (alq->aq_flags & AQ_ORDERED)
			waitchan = &alq->aq_waiters;
		else
			waitchan = alq;
	} else
		waitchan = NULL;

	ALQ_UNLOCK(alq);

	if (activate) {
		ALD_LOCK();
		ald_activate(alq);
		ALD_UNLOCK();
	}

	/* NB: We rely on wakeup_one waking threads in a FIFO manner. */
	if (waitchan != NULL)
		wakeup_one(waitchan);
}

void
alq_flush(struct alq *alq)
{
	int needwakeup = 0;

	ALD_LOCK();
	ALQ_LOCK(alq);

	/*
	 * Pull the lever iff there is data to flush and we're
	 * not already in the middle of a flush operation.
	 */
	if (HAS_PENDING_DATA(alq) && !(alq->aq_flags & AQ_FLUSHING)) {
		if (alq->aq_flags & AQ_ACTIVE)
			ald_deactivate(alq);

		ALD_UNLOCK();
		needwakeup = alq_doio(alq);
	} else
		ALD_UNLOCK();

	ALQ_UNLOCK(alq);

	if (needwakeup)
		wakeup_one(alq);
}

/*
 * Flush remaining data, close the file and free all resources.
 */
void
alq_close(struct alq *alq)
{
	/* Only flush and destroy alq if not already shutting down. */
	if (ald_rem(alq) == 0)
		alq_destroy(alq);
}

static int
alq_load_handler(module_t mod, int what, void *arg)
{
	int ret;
	
	ret = 0;

	switch (what) {
	case MOD_LOAD:
	case MOD_SHUTDOWN:
		break;

	case MOD_QUIESCE:
		ALD_LOCK();
		/* Only allow unload if there are no open queues. */
		if (LIST_FIRST(&ald_queues) == NULL) {
			ald_shutingdown = 1;
			ALD_UNLOCK();
			EVENTHANDLER_DEREGISTER(shutdown_pre_sync,
			    alq_eventhandler_tag);
			ald_shutdown(NULL, 0);
			mtx_destroy(&ald_mtx);
		} else {
			ALD_UNLOCK();
			ret = EBUSY;
		}
		break;

	case MOD_UNLOAD:
		/* If MOD_QUIESCE failed we must fail here too. */
		if (ald_shutingdown == 0)
			ret = EBUSY;
		break;

	default:
		ret = EINVAL;
		break;
	}

	return (ret);
}

static moduledata_t alq_mod =
{
	"alq",
	alq_load_handler,
	NULL
};

DECLARE_MODULE(alq, alq_mod, SI_SUB_SMP, SI_ORDER_ANY);
MODULE_VERSION(alq, 1);
OpenPOWER on IntegriCloud