summaryrefslogtreecommitdiffstats
path: root/drivers/scsi/scsi.c
blob: 1bf274e3b2b614b5331f4a082668e660ceba74e7 (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
/*
 *  scsi.c Copyright (C) 1992 Drew Eckhardt
 *         Copyright (C) 1993, 1994, 1995, 1999 Eric Youngdale
 *         Copyright (C) 2002, 2003 Christoph Hellwig
 *
 *  generic mid-level SCSI driver
 *      Initial versions: Drew Eckhardt
 *      Subsequent revisions: Eric Youngdale
 *
 *  <drew@colorado.edu>
 *
 *  Bug correction thanks go to :
 *      Rik Faith <faith@cs.unc.edu>
 *      Tommy Thorn <tthorn>
 *      Thomas Wuensche <tw@fgb1.fgb.mw.tu-muenchen.de>
 *
 *  Modified by Eric Youngdale eric@andante.org or ericy@gnu.ai.mit.edu to
 *  add scatter-gather, multiple outstanding request, and other
 *  enhancements.
 *
 *  Native multichannel, wide scsi, /proc/scsi and hot plugging
 *  support added by Michael Neuffer <mike@i-connect.net>
 *
 *  Added request_module("scsi_hostadapter") for kerneld:
 *  (Put an "alias scsi_hostadapter your_hostadapter" in /etc/modprobe.conf)
 *  Bjorn Ekwall  <bj0rn@blox.se>
 *  (changed to kmod)
 *
 *  Major improvements to the timeout, abort, and reset processing,
 *  as well as performance modifications for large queue depths by
 *  Leonard N. Zubkoff <lnz@dandelion.com>
 *
 *  Converted cli() code to spinlocks, Ingo Molnar
 *
 *  Jiffies wrap fixes (host->resetting), 3 Dec 1998 Andrea Arcangeli
 *
 *  out_of_space hacks, D. Gilbert (dpg) 990608
 */

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/completion.h>
#include <linux/unistd.h>
#include <linux/spinlock.h>
#include <linux/kmod.h>
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/async.h>
#include <asm/unaligned.h>

#include <scsi/scsi.h>
#include <scsi/scsi_cmnd.h>
#include <scsi/scsi_dbg.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_driver.h>
#include <scsi/scsi_eh.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi_tcq.h>

#include "scsi_priv.h"
#include "scsi_logging.h"

#define CREATE_TRACE_POINTS
#include <trace/events/scsi.h>

/*
 * Definitions and constants.
 */

/*
 * Note - the initial logging level can be set here to log events at boot time.
 * After the system is up, you may enable logging via the /proc interface.
 */
unsigned int scsi_logging_level;
#if defined(CONFIG_SCSI_LOGGING)
EXPORT_SYMBOL(scsi_logging_level);
#endif

/* sd, scsi core and power management need to coordinate flushing async actions */
ASYNC_DOMAIN(scsi_sd_probe_domain);
EXPORT_SYMBOL(scsi_sd_probe_domain);

/*
 * Separate domain (from scsi_sd_probe_domain) to maximize the benefit of
 * asynchronous system resume operations.  It is marked 'exclusive' to avoid
 * being included in the async_synchronize_full() that is invoked by
 * dpm_resume()
 */
ASYNC_DOMAIN_EXCLUSIVE(scsi_sd_pm_domain);
EXPORT_SYMBOL(scsi_sd_pm_domain);

/**
 * scsi_put_command - Free a scsi command block
 * @cmd: command block to free
 *
 * Returns:	Nothing.
 *
 * Notes:	The command must not belong to any lists.
 */
void scsi_put_command(struct scsi_cmnd *cmd)
{
	scsi_del_cmd_from_list(cmd);
	BUG_ON(delayed_work_pending(&cmd->abort_work));
}

#ifdef CONFIG_SCSI_LOGGING
void scsi_log_send(struct scsi_cmnd *cmd)
{
	unsigned int level;

	/*
	 * If ML QUEUE log level is greater than or equal to:
	 *
	 * 1: nothing (match completion)
	 *
	 * 2: log opcode + command of all commands + cmd address
	 *
	 * 3: same as 2
	 *
	 * 4: same as 3
	 */
	if (unlikely(scsi_logging_level)) {
		level = SCSI_LOG_LEVEL(SCSI_LOG_MLQUEUE_SHIFT,
				       SCSI_LOG_MLQUEUE_BITS);
		if (level > 1) {
			scmd_printk(KERN_INFO, cmd,
				    "Send: scmd 0x%p\n", cmd);
			scsi_print_command(cmd);
		}
	}
}

void scsi_log_completion(struct scsi_cmnd *cmd, int disposition)
{
	unsigned int level;

	/*
	 * If ML COMPLETE log level is greater than or equal to:
	 *
	 * 1: log disposition, result, opcode + command, and conditionally
	 * sense data for failures or non SUCCESS dispositions.
	 *
	 * 2: same as 1 but for all command completions.
	 *
	 * 3: same as 2
	 *
	 * 4: same as 3 plus dump extra junk
	 */
	if (unlikely(scsi_logging_level)) {
		level = SCSI_LOG_LEVEL(SCSI_LOG_MLCOMPLETE_SHIFT,
				       SCSI_LOG_MLCOMPLETE_BITS);
		if (((level > 0) && (cmd->result || disposition != SUCCESS)) ||
		    (level > 1)) {
			scsi_print_result(cmd, "Done", disposition);
			scsi_print_command(cmd);
			if (status_byte(cmd->result) & CHECK_CONDITION)
				scsi_print_sense(cmd);
			if (level > 3)
				scmd_printk(KERN_INFO, cmd,
					    "scsi host busy %d failed %d\n",
					    atomic_read(&cmd->device->host->host_busy),
					    cmd->device->host->host_failed);
		}
	}
}
#endif

/**
 * scsi_cmd_get_serial - Assign a serial number to a command
 * @host: the scsi host
 * @cmd: command to assign serial number to
 *
 * Description: a serial number identifies a request for error recovery
 * and debugging purposes.  Protected by the Host_Lock of host.
 */
void scsi_cmd_get_serial(struct Scsi_Host *host, struct scsi_cmnd *cmd)
{
	cmd->serial_number = host->cmd_serial_number++;
	if (cmd->serial_number == 0) 
		cmd->serial_number = host->cmd_serial_number++;
}
EXPORT_SYMBOL(scsi_cmd_get_serial);

/**
 * scsi_finish_command - cleanup and pass command back to upper layer
 * @cmd: the command
 *
 * Description: Pass command off to upper layer for finishing of I/O
 *              request, waking processes that are waiting on results,
 *              etc.
 */
void scsi_finish_command(struct scsi_cmnd *cmd)
{
	struct scsi_device *sdev = cmd->device;
	struct scsi_target *starget = scsi_target(sdev);
	struct Scsi_Host *shost = sdev->host;
	struct scsi_driver *drv;
	unsigned int good_bytes;

	scsi_device_unbusy(sdev);

	/*
	 * Clear the flags that say that the device/target/host is no longer
	 * capable of accepting new commands.
	 */
	if (atomic_read(&shost->host_blocked))
		atomic_set(&shost->host_blocked, 0);
	if (atomic_read(&starget->target_blocked))
		atomic_set(&starget->target_blocked, 0);
	if (atomic_read(&sdev->device_blocked))
		atomic_set(&sdev->device_blocked, 0);

	/*
	 * If we have valid sense information, then some kind of recovery
	 * must have taken place.  Make a note of this.
	 */
	if (SCSI_SENSE_VALID(cmd))
		cmd->result |= (DRIVER_SENSE << 24);

	SCSI_LOG_MLCOMPLETE(4, sdev_printk(KERN_INFO, sdev,
				"Notifying upper driver of completion "
				"(result %x)\n", cmd->result));

	good_bytes = scsi_bufflen(cmd);
        if (!blk_rq_is_passthrough(cmd->request)) {
		int old_good_bytes = good_bytes;
		drv = scsi_cmd_to_driver(cmd);
		if (drv->done)
			good_bytes = drv->done(cmd);
		/*
		 * USB may not give sense identifying bad sector and
		 * simply return a residue instead, so subtract off the
		 * residue if drv->done() error processing indicates no
		 * change to the completion length.
		 */
		if (good_bytes == old_good_bytes)
			good_bytes -= scsi_get_resid(cmd);
	}
	scsi_io_completion(cmd, good_bytes);
}

/**
 * scsi_change_queue_depth - change a device's queue depth
 * @sdev: SCSI Device in question
 * @depth: number of commands allowed to be queued to the driver
 *
 * Sets the device queue depth and returns the new value.
 */
int scsi_change_queue_depth(struct scsi_device *sdev, int depth)
{
	if (depth > 0) {
		sdev->queue_depth = depth;
		wmb();
	}

	if (sdev->request_queue)
		blk_set_queue_depth(sdev->request_queue, depth);

	return sdev->queue_depth;
}
EXPORT_SYMBOL(scsi_change_queue_depth);

/**
 * scsi_track_queue_full - track QUEUE_FULL events to adjust queue depth
 * @sdev: SCSI Device in question
 * @depth: Current number of outstanding SCSI commands on this device,
 *         not counting the one returned as QUEUE_FULL.
 *
 * Description:	This function will track successive QUEUE_FULL events on a
 * 		specific SCSI device to determine if and when there is a
 * 		need to adjust the queue depth on the device.
 *
 * Returns:	0 - No change needed, >0 - Adjust queue depth to this new depth,
 * 		-1 - Drop back to untagged operation using host->cmd_per_lun
 * 			as the untagged command depth
 *
 * Lock Status:	None held on entry
 *
 * Notes:	Low level drivers may call this at any time and we will do
 * 		"The Right Thing."  We are interrupt context safe.
 */
int scsi_track_queue_full(struct scsi_device *sdev, int depth)
{

	/*
	 * Don't let QUEUE_FULLs on the same
	 * jiffies count, they could all be from
	 * same event.
	 */
	if ((jiffies >> 4) == (sdev->last_queue_full_time >> 4))
		return 0;

	sdev->last_queue_full_time = jiffies;
	if (sdev->last_queue_full_depth != depth) {
		sdev->last_queue_full_count = 1;
		sdev->last_queue_full_depth = depth;
	} else {
		sdev->last_queue_full_count++;
	}

	if (sdev->last_queue_full_count <= 10)
		return 0;

	return scsi_change_queue_depth(sdev, depth);
}
EXPORT_SYMBOL(scsi_track_queue_full);

/**
 * scsi_vpd_inquiry - Request a device provide us with a VPD page
 * @sdev: The device to ask
 * @buffer: Where to put the result
 * @page: Which Vital Product Data to return
 * @len: The length of the buffer
 *
 * This is an internal helper function.  You probably want to use
 * scsi_get_vpd_page instead.
 *
 * Returns size of the vpd page on success or a negative error number.
 */
static int scsi_vpd_inquiry(struct scsi_device *sdev, unsigned char *buffer,
							u8 page, unsigned len)
{
	int result;
	unsigned char cmd[16];

	if (len < 4)
		return -EINVAL;

	cmd[0] = INQUIRY;
	cmd[1] = 1;		/* EVPD */
	cmd[2] = page;
	cmd[3] = len >> 8;
	cmd[4] = len & 0xff;
	cmd[5] = 0;		/* Control byte */

	/*
	 * I'm not convinced we need to try quite this hard to get VPD, but
	 * all the existing users tried this hard.
	 */
	result = scsi_execute_req(sdev, cmd, DMA_FROM_DEVICE, buffer,
				  len, NULL, 30 * HZ, 3, NULL);
	if (result)
		return -EIO;

	/* Sanity check that we got the page back that we asked for */
	if (buffer[1] != page)
		return -EIO;

	return get_unaligned_be16(&buffer[2]) + 4;
}

/**
 * scsi_get_vpd_page - Get Vital Product Data from a SCSI device
 * @sdev: The device to ask
 * @page: Which Vital Product Data to return
 * @buf: where to store the VPD
 * @buf_len: number of bytes in the VPD buffer area
 *
 * SCSI devices may optionally supply Vital Product Data.  Each 'page'
 * of VPD is defined in the appropriate SCSI document (eg SPC, SBC).
 * If the device supports this VPD page, this routine returns a pointer
 * to a buffer containing the data from that page.  The caller is
 * responsible for calling kfree() on this pointer when it is no longer
 * needed.  If we cannot retrieve the VPD page this routine returns %NULL.
 */
int scsi_get_vpd_page(struct scsi_device *sdev, u8 page, unsigned char *buf,
		      int buf_len)
{
	int i, result;

	if (sdev->skip_vpd_pages)
		goto fail;

	/* Ask for all the pages supported by this device */
	result = scsi_vpd_inquiry(sdev, buf, 0, buf_len);
	if (result < 4)
		goto fail;

	/* If the user actually wanted this page, we can skip the rest */
	if (page == 0)
		return 0;

	for (i = 4; i < min(result, buf_len); i++)
		if (buf[i] == page)
			goto found;

	if (i < result && i >= buf_len)
		/* ran off the end of the buffer, give us benefit of doubt */
		goto found;
	/* The device claims it doesn't support the requested page */
	goto fail;

 found:
	result = scsi_vpd_inquiry(sdev, buf, page, buf_len);
	if (result < 0)
		goto fail;

	return 0;

 fail:
	return -EINVAL;
}
EXPORT_SYMBOL_GPL(scsi_get_vpd_page);

/**
 * scsi_attach_vpd - Attach Vital Product Data to a SCSI device structure
 * @sdev: The device to ask
 *
 * Attach the 'Device Identification' VPD page (0x83) and the
 * 'Unit Serial Number' VPD page (0x80) to a SCSI device
 * structure. This information can be used to identify the device
 * uniquely.
 */
void scsi_attach_vpd(struct scsi_device *sdev)
{
	int result, i;
	int vpd_len = SCSI_VPD_PG_LEN;
	int pg80_supported = 0;
	int pg83_supported = 0;
	unsigned char __rcu *vpd_buf, *orig_vpd_buf = NULL;

	if (!scsi_device_supports_vpd(sdev))
		return;

retry_pg0:
	vpd_buf = kmalloc(vpd_len, GFP_KERNEL);
	if (!vpd_buf)
		return;

	/* Ask for all the pages supported by this device */
	result = scsi_vpd_inquiry(sdev, vpd_buf, 0, vpd_len);
	if (result < 0) {
		kfree(vpd_buf);
		return;
	}
	if (result > vpd_len) {
		vpd_len = result;
		kfree(vpd_buf);
		goto retry_pg0;
	}

	for (i = 4; i < result; i++) {
		if (vpd_buf[i] == 0x80)
			pg80_supported = 1;
		if (vpd_buf[i] == 0x83)
			pg83_supported = 1;
	}
	kfree(vpd_buf);
	vpd_len = SCSI_VPD_PG_LEN;

	if (pg80_supported) {
retry_pg80:
		vpd_buf = kmalloc(vpd_len, GFP_KERNEL);
		if (!vpd_buf)
			return;

		result = scsi_vpd_inquiry(sdev, vpd_buf, 0x80, vpd_len);
		if (result < 0) {
			kfree(vpd_buf);
			return;
		}
		if (result > vpd_len) {
			vpd_len = result;
			kfree(vpd_buf);
			goto retry_pg80;
		}
		mutex_lock(&sdev->inquiry_mutex);
		orig_vpd_buf = sdev->vpd_pg80;
		sdev->vpd_pg80_len = result;
		rcu_assign_pointer(sdev->vpd_pg80, vpd_buf);
		mutex_unlock(&sdev->inquiry_mutex);
		synchronize_rcu();
		if (orig_vpd_buf) {
			kfree(orig_vpd_buf);
			orig_vpd_buf = NULL;
		}
		vpd_len = SCSI_VPD_PG_LEN;
	}

	if (pg83_supported) {
retry_pg83:
		vpd_buf = kmalloc(vpd_len, GFP_KERNEL);
		if (!vpd_buf)
			return;

		result = scsi_vpd_inquiry(sdev, vpd_buf, 0x83, vpd_len);
		if (result < 0) {
			kfree(vpd_buf);
			return;
		}
		if (result > vpd_len) {
			vpd_len = result;
			kfree(vpd_buf);
			goto retry_pg83;
		}
		mutex_lock(&sdev->inquiry_mutex);
		orig_vpd_buf = sdev->vpd_pg83;
		sdev->vpd_pg83_len = result;
		rcu_assign_pointer(sdev->vpd_pg83, vpd_buf);
		mutex_unlock(&sdev->inquiry_mutex);
		synchronize_rcu();
		if (orig_vpd_buf)
			kfree(orig_vpd_buf);
	}
}

/**
 * scsi_report_opcode - Find out if a given command opcode is supported
 * @sdev:	scsi device to query
 * @buffer:	scratch buffer (must be at least 20 bytes long)
 * @len:	length of buffer
 * @opcode:	opcode for command to look up
 *
 * Uses the REPORT SUPPORTED OPERATION CODES to look up the given
 * opcode. Returns -EINVAL if RSOC fails, 0 if the command opcode is
 * unsupported and 1 if the device claims to support the command.
 */
int scsi_report_opcode(struct scsi_device *sdev, unsigned char *buffer,
		       unsigned int len, unsigned char opcode)
{
	unsigned char cmd[16];
	struct scsi_sense_hdr sshdr;
	int result;

	if (sdev->no_report_opcodes || sdev->scsi_level < SCSI_SPC_3)
		return -EINVAL;

	memset(cmd, 0, 16);
	cmd[0] = MAINTENANCE_IN;
	cmd[1] = MI_REPORT_SUPPORTED_OPERATION_CODES;
	cmd[2] = 1;		/* One command format */
	cmd[3] = opcode;
	put_unaligned_be32(len, &cmd[6]);
	memset(buffer, 0, len);

	result = scsi_execute_req(sdev, cmd, DMA_FROM_DEVICE, buffer, len,
				  &sshdr, 30 * HZ, 3, NULL);

	if (result && scsi_sense_valid(&sshdr) &&
	    sshdr.sense_key == ILLEGAL_REQUEST &&
	    (sshdr.asc == 0x20 || sshdr.asc == 0x24) && sshdr.ascq == 0x00)
		return -EINVAL;

	if ((buffer[1] & 3) == 3) /* Command supported */
		return 1;

	return 0;
}
EXPORT_SYMBOL(scsi_report_opcode);

/**
 * scsi_device_get  -  get an additional reference to a scsi_device
 * @sdev:	device to get a reference to
 *
 * Description: Gets a reference to the scsi_device and increments the use count
 * of the underlying LLDD module.  You must hold host_lock of the
 * parent Scsi_Host or already have a reference when calling this.
 *
 * This will fail if a device is deleted or cancelled, or when the LLD module
 * is in the process of being unloaded.
 */
int scsi_device_get(struct scsi_device *sdev)
{
	if (sdev->sdev_state == SDEV_DEL || sdev->sdev_state == SDEV_CANCEL)
		goto fail;
	if (!get_device(&sdev->sdev_gendev))
		goto fail;
	if (!try_module_get(sdev->host->hostt->module))
		goto fail_put_device;
	return 0;

fail_put_device:
	put_device(&sdev->sdev_gendev);
fail:
	return -ENXIO;
}
EXPORT_SYMBOL(scsi_device_get);

/**
 * scsi_device_put  -  release a reference to a scsi_device
 * @sdev:	device to release a reference on.
 *
 * Description: Release a reference to the scsi_device and decrements the use
 * count of the underlying LLDD module.  The device is freed once the last
 * user vanishes.
 */
void scsi_device_put(struct scsi_device *sdev)
{
	module_put(sdev->host->hostt->module);
	put_device(&sdev->sdev_gendev);
}
EXPORT_SYMBOL(scsi_device_put);

/* helper for shost_for_each_device, see that for documentation */
struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *shost,
					   struct scsi_device *prev)
{
	struct list_head *list = (prev ? &prev->siblings : &shost->__devices);
	struct scsi_device *next = NULL;
	unsigned long flags;

	spin_lock_irqsave(shost->host_lock, flags);
	while (list->next != &shost->__devices) {
		next = list_entry(list->next, struct scsi_device, siblings);
		/* skip devices that we can't get a reference to */
		if (!scsi_device_get(next))
			break;
		next = NULL;
		list = list->next;
	}
	spin_unlock_irqrestore(shost->host_lock, flags);

	if (prev)
		scsi_device_put(prev);
	return next;
}
EXPORT_SYMBOL(__scsi_iterate_devices);

/**
 * starget_for_each_device  -  helper to walk all devices of a target
 * @starget:	target whose devices we want to iterate over.
 * @data:	Opaque passed to each function call.
 * @fn:		Function to call on each device
 *
 * This traverses over each device of @starget.  The devices have
 * a reference that must be released by scsi_host_put when breaking
 * out of the loop.
 */
void starget_for_each_device(struct scsi_target *starget, void *data,
		     void (*fn)(struct scsi_device *, void *))
{
	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
	struct scsi_device *sdev;

	shost_for_each_device(sdev, shost) {
		if ((sdev->channel == starget->channel) &&
		    (sdev->id == starget->id))
			fn(sdev, data);
	}
}
EXPORT_SYMBOL(starget_for_each_device);

/**
 * __starget_for_each_device - helper to walk all devices of a target (UNLOCKED)
 * @starget:	target whose devices we want to iterate over.
 * @data:	parameter for callback @fn()
 * @fn:		callback function that is invoked for each device
 *
 * This traverses over each device of @starget.  It does _not_
 * take a reference on the scsi_device, so the whole loop must be
 * protected by shost->host_lock.
 *
 * Note:  The only reason why drivers would want to use this is because
 * they need to access the device list in irq context.  Otherwise you
 * really want to use starget_for_each_device instead.
 **/
void __starget_for_each_device(struct scsi_target *starget, void *data,
			       void (*fn)(struct scsi_device *, void *))
{
	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
	struct scsi_device *sdev;

	__shost_for_each_device(sdev, shost) {
		if ((sdev->channel == starget->channel) &&
		    (sdev->id == starget->id))
			fn(sdev, data);
	}
}
EXPORT_SYMBOL(__starget_for_each_device);

/**
 * __scsi_device_lookup_by_target - find a device given the target (UNLOCKED)
 * @starget:	SCSI target pointer
 * @lun:	SCSI Logical Unit Number
 *
 * Description: Looks up the scsi_device with the specified @lun for a given
 * @starget.  The returned scsi_device does not have an additional
 * reference.  You must hold the host's host_lock over this call and
 * any access to the returned scsi_device. A scsi_device in state
 * SDEV_DEL is skipped.
 *
 * Note:  The only reason why drivers should use this is because
 * they need to access the device list in irq context.  Otherwise you
 * really want to use scsi_device_lookup_by_target instead.
 **/
struct scsi_device *__scsi_device_lookup_by_target(struct scsi_target *starget,
						   u64 lun)
{
	struct scsi_device *sdev;

	list_for_each_entry(sdev, &starget->devices, same_target_siblings) {
		if (sdev->sdev_state == SDEV_DEL)
			continue;
		if (sdev->lun ==lun)
			return sdev;
	}

	return NULL;
}
EXPORT_SYMBOL(__scsi_device_lookup_by_target);

/**
 * scsi_device_lookup_by_target - find a device given the target
 * @starget:	SCSI target pointer
 * @lun:	SCSI Logical Unit Number
 *
 * Description: Looks up the scsi_device with the specified @lun for a given
 * @starget.  The returned scsi_device has an additional reference that
 * needs to be released with scsi_device_put once you're done with it.
 **/
struct scsi_device *scsi_device_lookup_by_target(struct scsi_target *starget,
						 u64 lun)
{
	struct scsi_device *sdev;
	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
	unsigned long flags;

	spin_lock_irqsave(shost->host_lock, flags);
	sdev = __scsi_device_lookup_by_target(starget, lun);
	if (sdev && scsi_device_get(sdev))
		sdev = NULL;
	spin_unlock_irqrestore(shost->host_lock, flags);

	return sdev;
}
EXPORT_SYMBOL(scsi_device_lookup_by_target);

/**
 * __scsi_device_lookup - find a device given the host (UNLOCKED)
 * @shost:	SCSI host pointer
 * @channel:	SCSI channel (zero if only one channel)
 * @id:		SCSI target number (physical unit number)
 * @lun:	SCSI Logical Unit Number
 *
 * Description: Looks up the scsi_device with the specified @channel, @id, @lun
 * for a given host. The returned scsi_device does not have an additional
 * reference.  You must hold the host's host_lock over this call and any access
 * to the returned scsi_device.
 *
 * Note:  The only reason why drivers would want to use this is because
 * they need to access the device list in irq context.  Otherwise you
 * really want to use scsi_device_lookup instead.
 **/
struct scsi_device *__scsi_device_lookup(struct Scsi_Host *shost,
		uint channel, uint id, u64 lun)
{
	struct scsi_device *sdev;

	list_for_each_entry(sdev, &shost->__devices, siblings) {
		if (sdev->sdev_state == SDEV_DEL)
			continue;
		if (sdev->channel == channel && sdev->id == id &&
				sdev->lun ==lun)
			return sdev;
	}

	return NULL;
}
EXPORT_SYMBOL(__scsi_device_lookup);

/**
 * scsi_device_lookup - find a device given the host
 * @shost:	SCSI host pointer
 * @channel:	SCSI channel (zero if only one channel)
 * @id:		SCSI target number (physical unit number)
 * @lun:	SCSI Logical Unit Number
 *
 * Description: Looks up the scsi_device with the specified @channel, @id, @lun
 * for a given host.  The returned scsi_device has an additional reference that
 * needs to be released with scsi_device_put once you're done with it.
 **/
struct scsi_device *scsi_device_lookup(struct Scsi_Host *shost,
		uint channel, uint id, u64 lun)
{
	struct scsi_device *sdev;
	unsigned long flags;

	spin_lock_irqsave(shost->host_lock, flags);
	sdev = __scsi_device_lookup(shost, channel, id, lun);
	if (sdev && scsi_device_get(sdev))
		sdev = NULL;
	spin_unlock_irqrestore(shost->host_lock, flags);

	return sdev;
}
EXPORT_SYMBOL(scsi_device_lookup);

MODULE_DESCRIPTION("SCSI core");
MODULE_LICENSE("GPL");

module_param(scsi_logging_level, int, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");

#ifdef CONFIG_SCSI_MQ_DEFAULT
bool scsi_use_blk_mq = true;
#else
bool scsi_use_blk_mq = false;
#endif
module_param_named(use_blk_mq, scsi_use_blk_mq, bool, S_IWUSR | S_IRUGO);

static int __init init_scsi(void)
{
	int error;

	error = scsi_init_queue();
	if (error)
		return error;
	error = scsi_init_procfs();
	if (error)
		goto cleanup_queue;
	error = scsi_init_devinfo();
	if (error)
		goto cleanup_procfs;
	error = scsi_init_hosts();
	if (error)
		goto cleanup_devlist;
	error = scsi_init_sysctl();
	if (error)
		goto cleanup_hosts;
	error = scsi_sysfs_register();
	if (error)
		goto cleanup_sysctl;

	scsi_netlink_init();

	printk(KERN_NOTICE "SCSI subsystem initialized\n");
	return 0;

cleanup_sysctl:
	scsi_exit_sysctl();
cleanup_hosts:
	scsi_exit_hosts();
cleanup_devlist:
	scsi_exit_devinfo();
cleanup_procfs:
	scsi_exit_procfs();
cleanup_queue:
	scsi_exit_queue();
	printk(KERN_ERR "SCSI subsystem failed to initialize, error = %d\n",
	       -error);
	return error;
}

static void __exit exit_scsi(void)
{
	scsi_netlink_exit();
	scsi_sysfs_unregister();
	scsi_exit_sysctl();
	scsi_exit_hosts();
	scsi_exit_devinfo();
	scsi_exit_procfs();
	scsi_exit_queue();
	async_unregister_domain(&scsi_sd_probe_domain);
}

subsys_initcall(init_scsi);
module_exit(exit_scsi);